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TRENDS IN EXTERNAL RADIATION EXPOSURE AMONG THE U.S NAVY MEDICAL PERSONNEL WORKING IN NUCLEAR MEDICINE DEPARTMENTS FROM 2003 TO 2020

A Thesis

submitted to the Faculty of the Graduate School of Arts and Sciences of Georgetown University

in partial fulfillment of the requirements for the degree of

Master of Science in Health Physics

By

TJahnensattudAennwt naarmSe. Almajed, B.S.

Washington, D.C. December 10, 2021

( viii )

CCooppyyrriigghhtt 2021 by Jannat Anwar S. Almajed All Rights Reserved

TRENDS IN EXTERNAL RADIATION EXPOSURE AMONG THE U.S NAVY MEDICAL PERSONNEL WORKING IN NUCLEAR MEDICINE DEPARTMENTS FROM 2003 TO 2020

SJatundneanttAnnamwear S. Almajed, B.S.

TThheessiissAAddvvisisoor rn:aLmueis Benevides, Ph.D.

ABSTRACT

Objectives: To assess trends in external occupational exposure of nuclear medicine (NM) workers from United States Navy (USN) medical centers from 2003 to 2020 and compare them with previously published data on NM workers from US civilian hospitals. Materials and methods: Analysis of the annual personal dose equivalents, deep dose equivalents Hp(10) (DDE) and shallow dose equivalents Hp(0.07) (skin dose) recorded using the DT-702/PD was conducted on 528 NM personnel working in USN medical centers. Also, analysis of 1,357 annual shallow dose equivalents Hp(0.07) (extremity dose) recorded using DXT-RAD was conducted on 285 NM workers. The data used in the study was provided by the United States Navy Dosimetry Center (NDC). Summary statistics of the distributions of annual and cumulative DDE, skin doses and extremity doses are provided in this study. Annual doses of nuclear medicine personnel working in Navy hospitals/clinics that perform PET imaging besides general nuclear medicine studies were identified using publicly available websites’ information, analyzed and compared with those who work in nuclear medicine facilities that perform only general NM studies. Doses from the two groups were compared using a two-sample t-test with 95% confidence interval. Results: Median annual doses of 0.38 mSv (IQR, 0.05-1.27 mSv; mean, 0.82 mSv), 0.37 mSv (IQR, 0.06 – 1.22 mSv; mean = 0.80 mSv), and 2.89 mSv (IQR = 0.76 – 7.86 mSv; mean = 6.65 mSv) for the DDE, skin dose and extremity dose, respectively, were observed in 2003–2020. Median cumulative

DDE, skin dose and extremity dose over 2003–2020 were 0.39 mSv (IQR = 0.05 – 3.18 mSv; mean = 2.96 mSv) and 0.39 mSv (IQR = 0.05 – 3.08 mSv; mean = 2.90 mSv), and 13.0 mSv (IQR

=2.89 – 38.5 mSv; mean = 31.6 mSv), respectively. Median annual DDE, skin and extremity doses to workers from identified PET facilities were 0.44 mSv (IQR= 0.06 – 1.60 mSv; mean = 0.99 mSv), 0.42 mSv (IQR = 0.06 – 1.58 mSv; mean = 0.97 mSv) and 3.16 mSv (IQR = 0.73 – 9.51

mSv; mean = 8.74 mSv), respectively, against 0.29 mSv (IQR = 0.06 – 0.95 mSv; mean = 0.65 mSv), 0.30 mSv (IQR =0.06 – 0.95 mSv; mean = 0.63 mSv) and 2.52 mSv (IQR = 0.76 – 6.19

mSv; mean = 4.72 mSv) to workers from non-PET facilities. The resultant p-value (p<0.05) of the two-sample t-test showed a significant difference between doses to NM workers from PET vs. non-PET facilities. Conclusions: All assessed values of the DDE, skin and extremity doses were well below the annual occupational limits established by the International Commissionon Radiological Protection. The median annual DDE to NM workers in the USN was lower than NM radiological technologists from US civilian hospitals. Our study’s mean annual skin dose was lower than NM technologists and NM physicians in Kuwait and NM technologists in Saudi Arabia. Moreover, our study's mean annual extremity dose was half the lowest extremity exposure recorded among NM workers in Serbia. As expected, working in PET facilities was associated with increased radiation doses. This study provided new data useful for future exposure assessment in this population of radiation workers and improved radiation protection programs in medical centers.

ACKNOWLEDGEMENTS

The research and writing of this thesis is dedicated to

everyone who helped along the way. I would like to express my deepest appreciation to my thesis mentor Dr. Daphnée Villoing who helped me through all stages of planning and writing my thesis. Many thanks to my thesis advisor Dr. Luis Benevides, who made this work possible by helping in providing the data and contacting the NDC on my behalf. Thanks to Dr. Timothy Jorgensen for his continuous support and help to finish my degree. Thanks to Dr. Stanley Fricke for his advice and willingness to help every time I ask.

My completion of this degree could not have been accomplished without the support of my family. I am extremely grateful to my husband Ahmad Al Marzook for his sacrifices, love, and encouragement. Thanks to my daughter Julia for her love and patience and all the time she waited for me. Thanks to my parents, sisters, and my brother for their support and prayers.

TABLE OF CONTENTS

Chapter 1: Introduction 1 Chapter 2: Background… 4 Ionizing radiation in medicine 4 Biological effects of ionizing radiation 4 Overview of nuclear medicine 6 Nuclear medicine imaging… 8 Nuclear cardiovascular imaging 8 Positron Emission Tomography 9 Occupational exposure in nuclear medicine 10 History in radiation protection 12 Dosimetry Concepts 13 Dose Units 13 External radiation dosimetry in the US-Navy… 14 Chapter 3: Materials and Methods 17 Data Collection 17 Institutional Review Board 18 Dosimetry dose readings 18 Data cleansing – Inclusion and Exclusion criteria 19 Annual dose calculation… 21 Cumulative dose calculation… 21 Categorization 21 Statistical analysis 22 Chapter 4: Results 23 Annual doses 23 Annual deep dose equivalents distribution 23 Annual skin dose equivalents distribution… 26 Annual extremity doses distribution… 29 Cumulative dose 32 Cumulative deep dose and skin dose equivalents distribution. 32 Cumulative extremity doses distribution… 32 PET and non-PET 32 PET facilities distribution… 32 Non-PET facilities distribution… 32 PET vs. non-PET 33 Chapter 5: Discussion… 37 Conclusions 42 Bibliography 44 Appendix A: Summary statistics of the annual deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020… 59 Appendix B: Yearly summary statistics of the annual deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities 60 Appendix C: Summary statistics of the annual shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003- 2020…………………………………………………………………………………………..…..66 Appendix D: Yearly summary statistics of the annual shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities 67 Appendix E: Summary statistics of the annual shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities 73 Appendix F: Yearly summary statistics of the annual shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities 74 Appendix G: Summary statistics of the cumulative deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003- 2020…………………………………………………………………………………………...….80 Appendix H: Summary statistics of the cumulative shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003- 2020… 81 Appendix I: Summary statistics of the cumulative shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities from 2003- 2020… 82 Appendix G: Summary statistics of the annual deep dose equivalents corresponding to 221 NM personnel working in USN medical facilities identified as PET facilities 83 Appendix K: Summary statistics of the shallow deep dose equivalents of the skin corresponding to 221 NM personnel working in USN medical facilities identified as PET facilities 84 Appendix L: Summary statistics of the shallow deep dose equivalents of the extremities corresponding to 163 NM personnel working in USN medical facilities identified as PET facilities 85 Appendix M: Summary statistics of the annual deep dose equivalents corresponding to 361 NM personnel working in USN medical facilities identified as non-PET facilities 86 Appendix N: Summary statistics of the annual shallow dose equivalents of the skin corresponding to 361 NM personnel working in USN medical facilities identified as non-PET facilities 87 Appendix O: Summary statistics of the annual shallow dose equivalents of the extremities corresponding to 176 NM personnel working in USN medical facilities identified as non-PET facilities 88 Appendix P: Two-sample t test’s result for the mean difference of the annual deep dose equivalents between non-PET and PET facilities 89 Appendix Q: Two-sample t test’s result for the mean difference of the annual shallow dose equivalents of the skin between non-PET and PET facilities 90 Appendix R: Two-sample t test’s result for the mean difference of the annual shallow dose equivalents of the extremities between non-PET and PET facilities 91 Appendix S: An example of a questionnaire could be used in future studies to help provide detailed information on the number of workers, workload, and radiation safety standards in the USN medical facilities 92

LIST OF FIGURES

Figure 1: DT-702 personal dosimeter 16

Figure 2: DXT-RAD finger dosimeter 16

Figure 3: Histogram of the distribution of 1,916 annual deep dose equivalents, Hp(10), previously collected and provided by the NDC for 528 workers from NM departments of the USN medical centers between 2003 and 2020. 24

Figure 4: Box-and-whisker plot of the trends in annual deep dose equivalents, Hp(10), to workers from NM departments of the USN medical centers between 2003 and 2020… 25

Figure 5: Histogram of the distribution of 1,916 annual shallow dose equivalents, Hp(0.07), previously collected and provided by the NDC for 528 workers from NM departments of the USN medical centers between 2003 and 2020… 27

Figure 6: Box-and-whisker plot of the trends in annual skin dose equivalents, Hp(0.07), to workers from NM departments of the USN medical centers between 2003 and 2020… 28

Figure 7: Histogram of the distribution of 1,357 annual shallow dose equivalents to the extremity, Hp(0.07), previously collected and provided by the NDC for 285 workers from NM departments of the USN medical centers between 2003 and 2020… 30

Figure 8: Box-and-whisker plot of the trends in annual shallow dose equivalents to the extremity, Hp(0.07), to workers from NM departments of the USN medical centers between 2003 and 2020… 31

Figure 9: Annual exposure of the personal dose equivalents Hp(10) in mSv for the USN personnel working NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT 34

Figure 10: Annual exposure of the personal dose equivalents Hp(0.07), skin doses, in mSv for the USN personnel working in NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT 35

Figure 11: Annual exposure of the personal dose equivalents Hp(0.07), extremity doses, in mSv for the USN personnel working in NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT… 36

LIST OF TABLES

Table 1. Annual Occupational Dose Limits 52

Table 2. Categories and corresponding definitions in the first dataset provided by the Navy Dosimetry Center, for DT-702/PD data 52

Table 3. Categories and corresponding definitions in the second dataset provided by the Navy Dosimetry Center, for DXT-RAD 53

Table 4. Several annual records in 2003–2020 used the DT-702/PD 53

Table 5. A yearly number of annual records in 2003–2020, using the DXT-RAD 54

Table 6. PET versus non-PET data, using the DT-702/PD 54

Table 7. PET versus non-PET data, using the DXT-RAD 55

Table 8. The number of observations, several workers, median, mean, Q1, Q3, and 95th percentiles, and the minimum to a maximum of various annual dose records for 2003-2020… 55

Table 9. Summary statistics of the annual dose records per year of the Hp(10). 55

Table 10. Summary statistics of the annual dose records per year of the skin dose equivalents, the Hp(0.07). 56

Table 11. Summary statistics of the annual dose records per year of the extremity dose equivalents, the Hp(0.07). 56

Table 12. The workers, median, mean, Q1, Q3, and 95th percentiles and minimum to a maximum of the cumulative deep dose equivalents, skin dose equivalents and extremity dose equivalents for 2003-2020… 57

Table 13. Summary statistics of the personal dose equivalents the Hp(10) and Hp(0.07) for the PET facilities' skin and extremity records 57

Table 14. Summary statistics of the personal dose equivalents Hp(10) and Hp(0.07) for skin and extremity records in the non-PET facilities 58

CHAPTER 1. INTRODUCTION

Nuclear medicine (NM) is a specialized area of radiology that experienced significant developments in the second half of the 20th century (1). The evolution of instrumentation, a surge of new radiopharmaceuticals (2), and the advent of Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) (3) have all contributed to the increased use of nuclear medicine worldwide and, more specifically in the United States (US) (2). The number of NM procedures performed worldwide increased from 23.5 million in 1980 (4) to 37 million in 2006 (5) and from 7 million in 1982 (6) to 17.2 million in 2006 in the United States (5). Hence, in 2006, about half of the worldwide NM procedures were performed in the United States (2). The tremendous increase in the performance of NM studies resulted in increasing the annual per-capita effective radiation dose to the US population (7), therefore increasing the occupational exposure among medical workers in NM departments (8).

Medical radiation workers are exposed to protracted low-level radiation for extended periods. In contrast to other medical radiation workers, NM technologists are in direct contact with the source of radiation by manipulating and handling radionuclides (9), which elevates their risk of certain cancers such as breast cancer and squamous cell carcinoma (SCC), and circulatory diseases such as myocardial infarction (10). Due to the possible risks from increased radiation exposure, the International Commission on Radiological Protection (ICRP) established recommendations to limit occupational doses and ensure the workers’ safety (11). It also emphasizes that the radiation exposure to the workers and patients should be kept As Low As Reasonably Achievable (ALARA) (12).

Previous studies of occupational doses to US radiologic technologists show that radiation doses have decreased since 1939 (13). Reducing these doses is likely due to improved radiation

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safety practices (11,14). However, a recent study involving NM technologists from nine US medical institutions showed that the maximum values of the annual personal dose equivalents generally increased from 1992 to 2015. In this study, the mean annual personal dose equivalent (2.69 mSv) was consistent with annual mean doses to NM technologists from other countries (1.5 to 3.5 mSv) and higher than the estimated annual mean effective dose to general medical workers worldwide (0.7 mSv) (15). Moreover, it was also higher than the mean annual dose to US radiologic technologists. Another recent study that examined dose trends among US radiologic technologists performing NM procedures or not over 36 years period showed that the annual dose records for US radiologic technologists performing NM procedures (median 1.2 mSv) were higher than for general radiologic workers (75th percentile= 0.40 mSv) (16). Finally, the study showed that higher doses were associated with performing more diagnostic NM procedures, specifically cardiac and PET procedures.

Variations in work practices and radiation safety techniques between institutions and countries can lead to heterogenous radiation exposure measurements among different groups of NM workers (14). For example, studies conducted in the US to examine the effect of the changes in NM practices on occupational doses included technologists from different medical institutions all over the country. Therefore, these studies are susceptible to heterogeneity and measurement biases due to the variations between NM departments regarding the radiation protection standards, the radiopharmaceuticals in use, and technology updates. The present study has the advantage of focusing specifically on exposures over time to a specific population of workers, all serving within the United States Navy (USN) -- a group of NM workers subject to the same radiation safety programs and regulations. This should significantly mitigate the problem of exposure heterogeneity within the study group.

Using a USN cohort of NM workers, this thesis tests the hypothesis that NM workers'

annual personal dose equivalents in USN medical centers are lower than NM workers' annual personal dose equivalents from civilian medical centers across the United States due to a stringent radiation protection program within the USN. Conclusions based on these results may help understand occupational exposure in nuclear medicine and improve radiation protection programs.

CHAPTER 2. BACKGROUND

1.1 Ionizing radiation in medicine

Radiation is energy; released from a source that travels through space in electromagnetic waves or particles. Radiation consists of ionizing radiation (IR) and non-ionizing radiation. This dissertation will focus on IR, a type of radiation with a short wavelength and enough energy to remove or relocate an electron from an atom. The whole population is naturally exposed to IR from the space, the earth, the air, and the radionuclides present in our bodies, such as Pottasium-

40. In the 1980s, eighty-two percent of the exposure to the U.S population was from natural background radiation (2).

In 1895, Wilhelm Roentgen accidentally discovered X-rays while experimenting on a cathode tube (17). Within a year of this discovery, X-rays were used in medicine for many applications, from finding a bullet in a patient's leg to diagnosing kidney stones (17). Two years later, X-rays started to be used in military hospitals (18). At the same period of X-ray discovery, other scientists such as Pierre and Marie Curie or Henri Becquerel were studying natural radiation (17). The Curies discovered polonium and radium, first used in industrial applications (17). Later, in 1946, manufactured sources of gamma radiation were also available. These discoveries and the invention of technologies in the medical field resulted in a new radiation exposure source to the population (17). Nowadays, about half of the radiation exposure (48%) to the U.S population comes from diagnostic and therapeutic medical applications (2).

1.2 Biological effects of ionizing radiation

Widespread unregulated use of IR was observed in the early years following its discovery. The lack of understanding of radiation-related risks on health led to severe injuries. Due to the late manifestation of detrimental radiation effects, the need for radiation safety was not immediately

recognized (19). First dermatitis and skin cancers were observed one and six years after discovering X-rays, respectively (18). Most of our understanding of radiation hazards came from the study of Atomic Bomb survivors after World War II (17).

When radiation interacts with the human body, the damage occurs at the cellular level, making it hard to detect (17). Radiation can cause two biological effects: deterministic (non- stochastic) and stochastic. Deterministic effects have a threshold: the severity of the response increases with the radiation dose, and below a certain dose threshold, no biological effect can occur (19). Some examples include skin burn, radiation sickness, sterility, and acute radiation syndrome (19). These effects depend on different variables such as the dose, dose fractionation, and type of radiation (19). In contrast, stochastic effects are random, and there is no threshold dose (19). The probability of the effect is proportional to the radiation dose, but the severity is independent (19). Cancer and heritable or genetic changes are the two main types of stochastic effects (19). As far as cancer is concerned, most cancers have a 20 year latency period and can occur after many years of exposure. Due to the long latency period, it is challenging to know whether the cancer was caused by radiation exposure or other factors.

There are different types of theoretical dose-response models related to the use ofany carcinogen, including radiation (20). The first is the linear no-threshold model, which states that there is a risk at any level of radiation exposure, no matter how small (20). This model is based on biological responses at high radiation doses (20). Still, because no clinical effects are seen from radiation exposure below 0.5 Gray (Gy), it is best to be conservative and take the low doses cautiously (20). The second model is the linear threshold which consists of a known threshold below no clinical effects are seen, but at the threshold level (0.5 Gy), the effect will increase linearly (20). The third model is the linear-quadratic, used for overall human response (20). This

model states that the effect is linear at low doses, but the response becomes quadratic as the dose increases. The NRC accepts the linear no-threshold model since it is the most conservative. It likely does not underestimate the actual risk, thereby allowing maximum protection when setting risk-based dose limits.

1.3 Overview of nuclear medicine

Nuclear medicine is a multi-disciplinary modality that involves administering radiopharmaceuticals for diagnostic and therapeutic purposes. Diagnostic nuclear medicine uses radioactive tracers to measure the function of an organ (physiological) and the biochemical; images in the body; in therapeutic nuclear medicine, unsealed radioactive materials are used to treat various thyroid cancer and hyperthyroidism. In nuclear medicine, radioactive chemical elements (radionuclides) can be used without any biological vector, such as iodine-131, or labeled with drugs or particles, forming a radiopharmaceutical (21).

Radiopharmaceuticals are radionuclides bound to biological molecules, targeting specific organs or tissues (22). They can be administered to the patient by intravenous or peritumoral injection, orally, or inhalation (2). Each NM imaging study corresponds to a specific radiotracer distributed in a targeted region of interest (ROI). The radiotracer emits gamma rays with given energies that can be detected by a gamma camera positioned next to the patient.

Most NM procedures focus on diagnostic, while therapeutic procedures only account for a small percentage (2). Therapeutic NM procedures are performed with a lower frequency than diagnostic NM procedures but with higher administered activities of radiopharmaceuticals (5). For example, the administered activity of iodine-131 for thyroid uptake study (diagnostic) is 2.8- 4.4 megabecquerel (MBq) (23), but 185-555 MBq for hyperthyroidism treatment (therapy) (24). However, since 1985, therapeutic NM procedures in developed countries have almost doubled (5).

Diagnostic NM studies can provide functional and anatomical information, whereas other diagnostic studies such as radiography or Computing Tomography (CT) usually provide just anatomical information (2). Diagnostic NM procedures can be divided into two categories based on technology and instrumentation: general diagnostic nuclear medicine and positron emission tomography (PET). In general diagnostic nuclear medicine, a gamma camera is used to obtain either planar imaging (two-dimensional projection image) or single-photon emission computed tomography (SPECT) imaging. In both cases, detectors collect gamma rays emanating from the patient after administering a radiotracer. The gamma camera rotates around the patient for SPECT imaging to record photons from different angles. A three-dimensional projection image is then reconstructed. Radiotracers used for planar and SPECT imaging emit low to medium energy photons (80-200 keV)(2).

Positron emission tomography (PET) was introduced at the end of the 1970s. In the early 1980s, the clinical applications of PET emerged in the field of neurology (25). In the early 1990s, PET was implemented in cardiology clinics (25). In the late 1990s, the F-18 fluorodeoxyglucose (FDG) began to be used for the evaluation of oncology patients, leading to rapid growth in the number of performed NM studies worldwide since 2000 (25) (5). This imaging technology relies on the administration of positron-emitting radionuclides and the detection of coincidence photons (i.e., 511 keV photons simultaneously emitted in opposite directions after a positron-electron annihilation) (5). The average annual growth rate of PET studies was 80 % from 2000 to 2005, against 9 % for non-PET NM diagnostic studies (21): the rapid growth in the PET studies was due to the introduction of the integrated PET/CT system in early 2000 and the use of F-18 FDG in oncology (25).

Hybrid imaging was introduced for both diagnostic and therapeutic applications (2). SPECT or PET imaging can be used in conjunction with conventional CT (SPECT/CT, PET/CT) (2), or more rarely, MRI (PET/MRI) (2), to obtain physiological images and to provide attenuation correction, which helps in improving the images by removing the effect of the artifact. Hybrid imaging techniques improve the accuracy of detecting and localizing disease and are increasingly used in recent years (2).

1.4 Nuclear medicine imaging

1.4.1 Nuclear cardiovascular imaging

Cardiac NM are non-invasive diagnostic procedures dedicated to assessing coronary artery disease and evaluating possible heart damage from cancer treatments such as radiotherapy and chemotherapy. NM cardiovascular studies have increased rapidly since 1979 and have become the most frequent procedure performed in nuclear medicine (1). In 2005, cardiac procedures accounted for 57% of the total completed NM studies in the US (5). The most common cardiac NM study is the myocardial perfusion stress test, which allows evaluation of the coronary arteries. Myocardial perfusion stress test performed in the US in 2014 accounted for 5.98 million studies (26).

Since the late 1960s, there have been few approved radiotracers used in nuclear cardiology (23). Nowadays, 59% of performed SPECT cardiac studies use Tc-99m Sestamibi (Tc-99m MIBI), 20% use Tc-99m Tetrofosmin, and 9% use Tl-201 Thallous Chloride (23). The amount of activity administered per procedure increased due to the reduction in the use of Tl-201 Thallous Chloride in myocardial NM studies. The typical administered amount of activity of Tl-201 Thallous Chloride before 2000 was 111 MBq and after 2000 is 148 MBq, while the administered amount of activity of Tc-99m MIBI and Tc-99m Tetrofosmin is 1110 MBq for one day protocol (23).

Furthermore, cardiac NM studies account for 85% of the effective dose to the NM patient population (5).

In 2011, a Turkish study estimated radiation doses to technologists per NM procedure (27). It showed that cardiac studies performed using Tc-99m MIBI delivered higher doses toNM technologists than whole-body bone scans, thyroid scans, and renal scans (27). The cumulative radiation exposure to technologists performing cardiac NM scans increased over time, which might be due to an increased frequency of cardiac procedures (1). Moreover, the myocardial perfusion stress test usually includes two injections, and technologists spend a longer time with the patient during injection, stress test, and camera positioning, contributing to increased occupational exposure (1).

1.4.2 Positron Emission Tomography

Positron emission tomography (PET) is a more recent NM technology. The science behind PET imaging started early in 1929 (28). Still, it was not clinically applicable until Ter-Pogossian et al. developed in 1975 a PET whole-body camera that provides high contrast images of positron- emitting organs (29). PET imaging relies on detecting photons emitted from the patient’s body after the injection of a positron-emitting radioisotope (29). When the emitted positron has lost its energy, it annihilates with an electron within the body to create two 511 keV photons (28). The PET camera is composed of scintillation crystals that absorb the photons and convert them into light photons. When two 511 keV photons are detected in coincidence (at 180° and simultaneously), the light is converted into an electrical signal (30).

Recently, the number of performed PET procedures increased from less than 2% to 15% due to several factors: the advent of the hybrid PET/CT system after 2000, an increasing number of cyclotrons for the production of short-lived positron-emitting radioisotopes (most positron

emitters have half-lives measured in minutes), and a decrease in the cost of PET cameras (2). Moreover, malignant tumors metabolize glucose faster than benign tumors, making F-18 FDG useful in oncology (28). The high demand for PET in oncology is also a leading cause of the increase in PET scans annually (31).

The annihilation photons from the radionuclides used in PET have a higher energy (511 keV) than the energy of the photons from radionuclides typically used in general NM studies. Accordingly, the annihilation photons have a greater ability to penetrate deeper tissues, which causes a higher internal organ risk to workers (31). An Australian study compared the radiation doses to technologists working in general NM with doses to those working in PET and showed that technologists rotating through PET received higher whole-body doses than those who only performed general NM procedures (31).

1.5 Occupational exposure in nuclear medicine

With ionizing radiation in medicine, medical workers are sometimes exposed. Those working in NM departments, including NM technologists, physicians, nurses, health/medical physicists, are more or less exposed to ionizing radiations depending on their occupationand workload. Occupational exposure occurs from any procedure that requires the worker to stand near a radioactive source during the shipping, preparation, or administration of the radiopharmaceutical. Furthermore, standing near the patient after the administration can also lead to radiation exposure (8). In the earliest years of nuclear medicine, scientists focused on improving the instrumentation, interpreting the medical images, and conducting clinical trials to approve new radiopharmaceuticals, with little attention to monitoring occupational exposure (8).

The US National Cancer Institute conducted a cohort study on 90,000 US radiologic technologists employed in the twentieth century (32) that showed increased risks of leukemia (33),

melanoma and non-melanoma skin cancer (34-35), and breast cancer (36), for these technologists. Another study showed a statistically significant increase in cancer mortality among British radiologists who had been working for more than 40 years in the twentieth century (37). A recent study of radiation-monitored workers employed in the nuclear industry in France, the United Kingdom, and the US showed a positive association between cumulative dose of ionizing radiation and death caused by leukemia among workers exposed to low doses of radiation (38). Compared with the nuclear industry, the medical field's lack of historical dosimetry data made it more challenging to estimate radiation risk among those workers (39). Starting in the 1950s, scientists became more aware of radiation's health hazards and gave more attention to occupational exposure. This awakening led to increasing the awareness of NM workers' monitoring (8).

NM workers are potentially exposed to radiation internally and externally. Internal radiation exposure can occur after inhalation, ingestion, or skin contamination with radionuclides (39). Individual monitoring for internal exposure to radiation is usually achieved by body activity assessment or air sampling (39). Doses from internal exposure during routine work in the NM department are much lesser than the external exposure (39). Therefore, the dose assessment for internal exposure to NM workers is only performed when an unanticipated event has possibly internally exposed the worker. Otherwise, NM workers are externally exposed to ionizing radiations during a typical workday due to the proximity with radioactive materials during transportation, manipulation, injection, and patients’ transportation, positioning, or imaging (39). For that reason, NM workers are regularly monitored for external radiation exposure by wearing two dosimeters: a whole-body dosimeter on the chest and an extremity dosimeter on the finger.

1.6 History in radiation protection

In the 1896s, the American engineer Wolfram Fuchs established the first radiation protection recommendations: time, distance, and shielding (18). In 1925, the first meeting of the International Congress of Radiology (ICR) was held in London, and the International Commission on Radiation Units and Measurements (ICRU) was established (18). In 1928, the International X- ray and Radium Protection Committee (IXRPC) provided its first recommendation, emphasizing the importance of shielding to protect against superficial injuries and changes in the blood, and set a limit of working hours (18). In 1934, the first set of exposure limits was established for X-ray irradiation (18). This recommendation (0.2 roentgen per day) can result in an annual effective dose of about 500 mSv (18). In 1938, the same exposure limits and regulations were adopted for gamma radiation as had previously been established for X-rays (18). After world war II, in 1951, the International Commission on Radiological Protection (ICRP) was established, and this commission issued a recommendation of a maximum permissible dose of 0.5 roentgens/week and

1.5 roentgen/week for both X-ray and gamma radiation for whole-body exposure and hand exposure, respectively (18).

For the first 60 years of using ionizing radiation in industry and medicine, the main goal in radiological protection was to avoid any deterministic effects on workers (18). During this time, the ICRU started to replace roentgen ( a unit of exposure) with rem ( a unit of dose equivalence), and the limit from 1951 became 0.3 rem /week, resulting in annual occupational effective dose of 150 mSv (18). In 1954, the commission provided the first recommendation that encourages limiting the exposure from IR to the lowest possible level (18). In 1958, following the Geneva meeting, the commission published its recommendation in publication 1, including a limit of accumulated dose equivalent corresponding to an average annual occupational effective dose of

50 mSv (18). The 1954 recommendation was replaced by as low as practicable in publication 9 in the 1966’s report, and the limit of accumulated dose equivalent was replaced by an annual occupational limit of 50 mSv (18). In 1977, the ICRP established a dose limitation system and introduced the three principles of protection: justification, optimization, and the application of annual occupational dose limits (the total effective dose equivalents and the dose equivalents). In 1990, the ICRP provided more specified numerical limits to protect workers (Table 1)(11). In the United States, the Nuclear Regulatory Commission (NRC) was created by congress in 1974 to regulate the use of nuclear materials and to ensure the safe use of radioactive materials for beneficial civilian purposes while protecting the environment and people. The current Navy radiation protection standards are consistent with or more stringent than those of the NRC.

1.7 Dosimetry concepts

1.7.1 Dose Units

The quantities used in radiation dosimetry are divided into three categories: physical quantities, which describe the interactions between the radiation and matter (40), protection quantities, and operational quantities, both used in radiation protection dosimetry (41). The ICRP has supported a system for radiological protection for more than 50 years (42). In 2007, the most recent protection quantities were recommended by the ICRP in publication 103, which include the mean absorbed dose, the equivalent dose, HT, and the effective dose, E (42). The equivalent dose is based on the mean absorbed dose multiplied by a radiation-weighting factor, which depends on the biological effectiveness of the type of radiation (43). After applying tissue-weighting factors, the effective dose is the sum of all exposed tissues' equivalent doses. The effective dose is used for protective dose assessment (43). It is calculated for a reference male or female but never for a specific individual.

Protection quantities are impossible to measure directly; therefore, equivalent doses and effective doses cannot be used directly in radiation monitoring but can be assessed using operational quantities (43). The ICRP and the ICRU defined operational quantities as replacing the protection quantities to ensure compliance with regulations and exposure limits to workers (44). Accordingly, many countries have used operational quantities for individual external radiation monitoring purposes (42). Although the operational quantities generally provide a conservative estimate for the protection quantities (42), the ICRU stated that they should be used as estimates for the protection quantities when doses are below dose limits (44).

Operational quantities consist of area monitoring quantities and a personal dose equivalent used for individual monitoring (42). For the present study, only the personal dose equivalent will be discussed. The personal dose equivalent, Hp (d), is a dose equivalent at an appropriate depth, d, below a specified point of the body (43). A depth of d= 10 mm is used for the deep dose equivalent (DDE-whole body), while a depth of d= 0.07 mm is used for the assessment of the shallow dose equivalent (SDE) to the skin and extremities (43). The relationship betweenthe effective dose and Hp(10) is based on a uniform whole-body irradiation (44). The deep dose equivalent Hp(10) is estimated for photons and electrons using a single detector whose output signals are proportional to the absorbed dose (44). The shallow dose equivalent Hp(0.07) is estimated using a thin detector material whose output signals are proportional to the absorbed dose to tissue and used for low-energy photons and beta particles monitoring (44).

1.7.2 External radiation dosimetry in the US-Navy

The US Navy (USN) specifies acceptable dosimetry devices for monitoring Navy radiation workers (45). All NM personnel working in the USN medical centers are required by the Navy regulations to wear personnel dosimeters (PDs). PDs are used to monitor DDE and SDE.

Simultaneously, some NM workers, such as NM technologists, must wear extremity dosimeters (45).

In 1973, the Navy introduced thermo-luminescent dosimeters (TLD) for gamma exposure monitoring. Since 2002, the Navy has been using a DT-702 manufactured by Saint Gobain (Harshaw 8840) for personnel dosimetry. It uses a high-sensitivity LiF doped with magnesium (Mg), copper (Cu), and phosphorus (P) (LiF: Mg, Cu, P) (45). The DT-702/PD is composed of a TLD card and a holder. The TLD includes four lithium fluoride (LiF) pellets of different thicknesses and compositions mounted between two Teflon sheets on an aluminum card (45).

Elements 1 and 2 are 0.381 mm thick of LiF-700H, element 3 is a thinner 0.254 mm of LiF-700H, and element 4 is 0.381 mm of LiF-600H (45) . LiF-700H can measure photon and beta radiation, while LiF-600H is useful for measuring photon, beta, and neutron radiation (45). The holder consists of filters that provide variable radiation absorption thicknesses to assess DDE and SDE (45). Element 1 is placed behind 242 mg/cm2 plastic combined with 91 mg/ cm2 copper and discriminates gamma radiation energy levels (46). Element 2 is placed behind 1,000 mg/cm2 of plastic and is used for determining the deep dose Hp(10) (46). Element 3 is covered by a 17 mg/cm2 Mylar window for shallow dose equivalent estimation (46). Element 4 is placed behind a combination of 242 mg/cm2 of plastic and 240 mg/ cm2 of Tin and used to provide neutron information as well as medium energy photon discrimination (46) (Figure 1). The NDC provides NM workers with Thermo scientific DXTRAD finger ring dosimeter for extremity monitoring. DXTRAD is a single element LiF TLD used to monitor photon and beta radiation and mounted in an adjustable ring (45) (Figure 2).

( Figure 4: DT-702 personal dosimeter. Cardholder Filter 2: Plastic Filter 3: Mylar window Filter 4: Plastic and Tin Filter 1: Plastic and Copper LiF Card )

Figure 5: DXT-RAD finger dosimeter.

*Image from (NAVMED P-5055, Radiation Health Protection Manual)

CHAPTER 3. MATERIALS AND METHODS

This study is designed to examine the changes in annual occupational exposure among a study population of NM personnel working in USN medical centers, using personal dose equivalents (deep and shallow) recorded from personnel passive dosimeters and shallow doses recorded from extremity dosimeters. A dosimetry dataset was received from the United States Navy, Naval Dosimetry Center (NDC), the centralized dosimetry processing laboratory for US Navy. NDC distributes, receives, processes, and archives exposures from the USN occupational workers deployed worldwide.

2.1 Data Collection

The NDC is a large-scale processor responsible for sending dosimeters to over250 locations worldwide (47) and preparing summary radiation exposure reports to the Navy and Marine Corps personnel (45). It provided two datasets that include dose records of NM personnel working in the USN medical centers over almost 20 years. The first dataset contains the radiation exposure obtained from personal dosimeters over 2002-2020. The second dataset contains radiation exposure obtained from extremity dosimeters over 2003-2020. The two datasets were provided as Microsoft Excel spreadsheets. Data used in this study are explained in Table 2-3.

Moreover, the Navy provides a 2-digit occupational code that identifies Navy employers' occupation: the assigned code is 32 for NM occupation (45). For this study, code 32 was usedby the NDC to extract Navy personnel working in NM departments. Radiation exposure monitoring data of NM personnel working in Naval medical centers from 2003 to 2020 were included in this study. The data collection period was set to 2000-2020, corresponding to the years when the exposure to NM workers was expected to increase due to the advent of PET/CT imaging. It also matches an increased use of Tc-99m in myocardial studies, which require higher administered

activities, as previously described (Background). However, as the USN transitioned to a new dosimeter in 2002, the NDC did not provide any data collected before that year.

2.2 Institutional Review Board

An institutional review board (IRB) is a group that a research center has formally designated to review and monitor research involving human subjects (48). They work to protect the rights and safety of humans who participate in the research. Georgetown University’s IRB reviewed this study's proposal under ID: STUDY00003615 and was determined as exempt (non- human research). As defined by the US Department of Health and Human Subjects under 45 CFR 26.101(b) (48) from 45 CFR part 46 requirements, an exempt study may include existing data, but the subjects cannot be identified from the information presented in the study. To fulfill this condition, the NDC deidentified data: name, age, gender, date of birth, or any other identifiers were not used in this study.

2.3 Dosimetry dose readings

The operational quantities Hp(d) (mSv) have been used in the applicable regulations of many countries for individual external monitoring to ensure workers' compliance with radiation safety (49). Collected dosimetry information for external radiation monitoring to radiation workers generally includes two dose quantities: Hp(10) and Hp(0.07), which are obtained from personal and extremity monitoring devices, respectively (15). The USN requires NM workers to wear the dosimeter at the waist/chest level for photon and beta radiation monitoring and a DXT-RAD finger ring dosimeter for extremity monitoring (45).

NM personnel working in Naval medical centers have been routinely monitored using TLD dosimeters since 1973 (45). Since 2002, the NDC has issued a personnel monitor (DT-702/PD) quarterly (95 days maximum) to monitor their radiation workers (45). Still, they monitored

monthly (35 days maximum) any NM technologist and other NM worker expected to receive an annual effective dose equivalent of 5 mSv (45).

The Navy does not keep the exact job title of their workers in records. In nuclear medicine, NM workers can be either technologists, nurses, physicians, or health/medical physicists, and this distinction could not be made in our data. No further investigation could be conducted to obtain this information for the sake of anonymity. Therefore, the monitoring time of the dose records varied based on the variation in the occupations in the NM department. Although, in the data, we observed monitoring times that exceeded 95 days in 360 records corresponding to 154 individuals working in 12 USN medical centers. Dosimetry data corresponding to extended periods of 95+ days was considered acceptable in this study; they were not excluded and believed to have no detrimental effect on our study.

The lower limit of detection (LLD) of the dosimeter DT-702/PD is 0.03 mSv for DDE and SDE for photon and beta monitoring and 0.05 mSv for DDE for neutron monitoring (50). As confirmed by NDC workers, the US Navy keeps all the recorded doses, including the doses below the LLD levels, for use in retrospective studies. Therefore, annual dose equivalents below and above the LLD level were included in the data analysis in this study.

2.4 Data cleansing – Inclusion and Exclusion criteria

The NDC provided whole-body exposure (deep dose equivalent, DDE) and skin exposure (shallow dose equivalent, SDE) data for 528 individuals working in NM departments of 16 Naval medical centers over 2002-2020: these data were recorded using the DT-702/PD. Besides, the NDC provided extremity exposure (SDE) data for 305 individuals working in NM departments of 15 Naval medical centers over 2003-2020: these data were recorded using DXT-RAD finger rings.

Henceforth, the SDE from personal dosimeters will be referred to as "skin dose," and the SDE from extremity dosimeters as "extremity dose."

Records before 2002 were excluded from this study because of a dosimetry technology transition and change in the Lower Limit of Detection in the Navy. NDC provided the data with a unique anonymized individual code to link each individual's data. These unique individual codes ensured anonymity of the individual workers. The data included from NDC included the issue date and the collection date of the dosimeters, which was used to convert period doses to annual doses, as explained in the next paragraph.

The initial dataset received from NDC included 7,641 records of each DDE and skin dose and 4,789 records of extremity doses. Duplicates were first identified in Excel using the following variables: unique code, issue date, and collection date. After the data cleansing, 7,578 records remained for DDE and skin doses and 4,747 for extremity doses. Overlaps between years were then tracked to avoid overestimating, and doses were recalculated by calendar year. For example, if the issue date was at the end of 2003 and the dosimeter was collected early in 2004, the total monitoring duration for this dosimeter was calculated by subtracting the issue date from the collection date. Then, the total number of days with a dose was derived for each calendar year. An average daily dose was then calculated by dividing the recorded dose by the total monitoring duration and eventually multiplied by the total number of days of that calendar year. 1,201 and 830 records were found to overlap between two years in the data from DT-702/PD and DXT-RAD dosimeters, respectively, which led to as many more new records in the datasets of these respective dosimeters. A total of 161 records of extremity doses from 20 individuals were excluded for not being linked to any individual from the whole-body data.

2.5 Annual dose calculation

The unique code and the issue year converted period doses to annual doses. All the available DDE values for each worker and each year were summed to obtain annual doses. The same step was taken to calculate annual skin and extremity doses. Doses provided in Roentgen equivalent man (rem) by the US Navy were converted into millisieverts (mSv). Yearly numbers of annual records are provided in Table 4-5.

2.6 Cumulative dose calculation

The cumulative personal dose equivalents were calculated by summing the annual records for each individual over the period a worker was exposed to radiation in USN NM departments. Five hundred twenty-eight cumulative doses of each DDE and skin records and 285 cumulative doses of extremity records were included in the analysis.

2.7 Categorization

The NDC provided the mailing address associated with each issued dosimeter, including the Navy medical center name, city, state, and zip codes. Data from DT-702/PD records corresponded to 16 locations, while data from DXT-RAD records corresponded to 15 sites. These addresses were used to discriminate PET and non-PET facilities, using publicly available Navy hospitals/clinics’ websites. Our research was focused on NM and PET features in the presentations of radiology departments. If the website mentioned both NM and PET, we categorized the facility as a PET facility; otherwise, it was categorized as a non-PET facility. More detailed information is provided in Tables 6-7. For 140 dose records corresponding to 78 individuals, all from 2003, dose data were excluded from our PET vs. non PET analysis due to the absence of a mailing address.

2.8 Statistical analysis

The statistical software STATA version 16 was used to analyze the data. The distributions of annual and cumulative dose records of NM personnel working in Naval medical centers from 2003-2020 were described using summary statistics (e.g., 25th, 50th, 75th, and 95th percentiles) and graphical methods (e.g., histograms and box-and-whisker plots). Owing to the large observation number within the PET and non-PET facilities, a parametric test was conducted without the necessity to perform a normality test. The F-ratio test for the equality of the variances was served with a 95% confidence interval (CI). It showed significant differences between the variances of the two groups: annual exposure of the personnel working in the USN NM facilities perform PET/CT vs. the annual exposure of personnel working in the USN NM facilities that do not perform PET/CT of all variables DDE, skin doses and extremity doses (p= < 0.05). Therefore, the DDE, skin doses, and extremity doses were statistically analyzed between both groups using the two-sample t-test, assuming unequal variance. For all statistical tests, p< 0.05 was considered statistically significant. The null hypothesis (i.e., the hypothesis to be tested) was no difference in the annual radiation exposure of personnel working in the USN NM facilities performing PET/CT vs. the annual exposure of personnel working in the USN NM facilities that do not perform PET/CT. The alternate hypothesis was a difference in the annual radiation exposure of personnel working in the USN NM facilities performing PET/CT vs. the annual exposure of personnel working in the USN NM facilities not performing PET/CT. (Rejection of the null hypothesis implies that the alternative hypothesis is correct).

CHAPTER 4. RESULTS

Summary statistics of annual dose records to NM workers from medical centers of the US Navy between 2003 and 2020 are presented in Table 8. A total of 1,916 and 1,357 annual dose records were obtained from 2003 to 2020 using the DT-702/PD and the DXT-RAD, respectively (Table 4-5). The numbers of annual records varied over time, with average values of 106 (37 –

159) and 75 (35 – 103) for DT-702/PD and DXT-RAD, respectively. The average number of annual records per NM worker were 3.63 and 4.76 for DT-702/PD and DXT-RAD, respectively.

3.1 Annual doses

3.1.1 Annual deep dose equivalents distribution

A total of 1,916 annual deep dose equivalents (Hp(10)) – recorded between 2003 and 2020 for 528 individuals – were included in the analysis. These annual Hp(10) varied from 0.00 mSv to

7.18 mSv, with a median value of 0.38 mSv (interquartile range [IQR], 0.05-1.27 mSv; mean, 0.82 mSv). Seventeen percent of the annual Hp(10) were below the LLD of the DT-702/PD but were included in the analysis. More than 95% of the annual Hp(10) received by NM workers in our cohort were below three mSv [95.3% (1827 of 1916])(Figure 3). Median annual Hp(10) remained relatively constant from 2003 to 2020 (range, 0.12-0.82 mSv) (Table 9). The distribution of the maximum value of annual Hp(10) fluctuated over time (range, 1.87-7.18 mSv), with the highest value observed in 2015 (Figure 4). No correlation was found between the number of individuals monitored each year and the maximum value.

Figure 3: Histogram of the distribution of 1,916 annual deep dose equivalents, Hp(10), previously collected and provided by the NDC for 528 workers from NM departments of the USN medical centers between 2003 and 2020.

Figure 4: Box-and-whisker plot of the trends in annual deep dose equivalents, Hp(10), to workers from NM departments of the USN medical centers between 2003 and 2020.

*The upper and lower whiskers represent the maximum and minimum values.

3.1.2 Annual skin dose equivalents distribution

A total of 1,916 annual skin dose equivalents (Hp(0.07)) recorded between 2003 and 2020 for 528 individuals were also included in the analysis. These annual Hp(0.07) varied from 0.00 mSv to 7.12 mSv, with a median value of 0.37 mSv (IQR =0.06 – 1.22 mSv; mean = 0.80 mSv). Sixteen percent of the annual Hp(0.07) were below the LLD of the DT-702/PD but were included in the analysis. More than 95% of the annual Hp(0.07) received by NM workers in our cohort were below three mSv [95.6% (1831 of 1916)] (Figure 5). Median annual Hp(0.07) remained relatively constant from 2003 to 2020 (range, 0.12-0.81 mSv) (Table 10). The distribution of the maximum value of annual Hp(0.07) fluctuated over time (range, 1.96-7.12 mSv), with the highest value observed in 2015 (Figure 6). No correlation was found between the number of individuals monitored each year and the maximum value.

Figure 5: Histogram of the distribution of 1,916 annual shallow dose equivalents, Hp(0.07), previously collected and provided by the NDC for 528 workers from NM departments of the US-Navy between 2003 and 2020.

Figure 6: Box-and-whisker plot of the trends in annual skin dose equivalents, Hp(0.07), to workers from NM departments of the USN medical centers between 2003 and 2020.

*The upper and lower whiskers represent the maximum and minimum values.

3.1.3 Annual extremity doses distribution

A total of 1,357 annual extremity dose equivalents (Hp(0.07)) recorded between 2003 and 2020 for 285 individuals were included in the analysis. These annual Hp(0.07) varied from 0.00 mSv to 121 mSv, with a median value of 2.89 mSv (IQR = 0.76 – 7.86 mSv; mean = 6.65 mSv). Almost eighty-two percent of the annual Hp(0.07) received by NM workers in our cohort were below ten mSv [81.7% (1109 of 1357)] (Figure 7). Median annual Hp(0.07) remained relatively constant from 2003 to 2020 (range, 1.34-5.26 mSv) (Table 11). The distribution of the maximum value of annual Hp(0.07) doubled in 2005 (120 mSv), then fluctuated in 2006 – 2014, and decreased again after 2015 to reach a minimum value of 12.7 mSv in 2020 (Figure 8). No correlation was found between the number of individuals monitored each year and the maximum value for the annual extremity doses.

Figure 7: Histogram of the distribution of 1,357 annual shallow dose equivalents to the extremity, Hp(0.07), previously collected and provided by the NDC for 285 workers from NM departments of the USN medical centers between 2003 and 2020

Figure 8: Box-and-whisker plot of the trends in annual shallow dose equivalents to the extremity, Hp(0.07), to workers from NM departments of the USN medical centers between 2003 and 2020.

*The upper and lower whiskers represent the maximum and minimum values.

3.2 Cumulative doses

3.2.1 Cumulative deep dose and skin dose equivalents distribution

For the 528 individuals monitored with the DT-702/PD, the cumulative deep dose equivalents (DDE) and cumulative skin dose equivalents ranged from 0.00 to 46.6 mSv and 0.00 to 44.3 mSv, respectively. Cumulative DDE and skin doses had median values of 0.39 mSv (IQR

= 0.05 – 3.18 mSv; mean = 2.96 mSv) and 0.39 mSv (IQR = 0.05 – 3.08 mSv; mean = 2.90 mSv), respectively (Table 12 a-b).

3.2.2 Cumulative extremity dose equivalents distribution

For the 285 individuals monitored with the DXT-RAD, the cumulative extremity dose equivalents ranged from 0.11 to 529 mSv and had a median value of 13.0 mSv (IQR= 2.89 – 38.5 mSv; mean = 31.6 mSv) (Table 12c).

3.3 PET and non-PET dose

3.3.1 PET facilities distribution

The analysis of the two facilities with a PET department included 221 individual and 787 annual dose records of both values the DDE and the skin dose equivalents, respectively, and 163 individual and 600 annual dose record of the extremity dose equivalents. DDE, skin dose equivalents and extremity dose equivalents had median values of 0.44 mSv (IQR= 0.06 – 1.60 mSv; mean = 0.99 mSv), 0.42 mSv (IQR = 0.06 – 1.58 mSv; mean = 0.97 mSv) and 3.16 mSv (IQR = 0.73 – 9.51 mSv; mean = 8.74 mSv), respectively (Table 13).

3.3.2 Non-PET facilities distribution

The analysis of the 14 and 13 facilities corresponding to the data from DT-702/PD and DXT-RAD dosimeters, respectively, were collected on 361 individuals, corresponding to 1,207

annual dose records of each the DDE and the skin dose equivalents, and 176 individuals, corresponding to 800 annual dose records of the extremity dose equivalents. DDE, skin dose equivalents and extremity dose equivalents had median values of 0.29 mSv (IQR = 0.06 – 0.95 mSv; mean = 0.65 mSv), 0.30 mSv (IQR= 0.06 – 0.95 mSv; mean = 0.63 mSv) and 2.52 mSv

(IQR = 0.76 – 6.19 mSv; mean = 4.72 mSv), respectively (Table 14).

3.3.3 PET vs non-PET

An independent two samples t-test was conducted to compare the annual radiation exposure of personnel working in the USN NM facilities perform PET/CT (group 1) (N=787 and N=600) vs. the annual exposure of personnel working in the USN NM facilities that do not perform PET/CT (group 2) (N= 1,207 and N= 800) for the data recorded using the DT-702/PD and the DXT-RAD, respectively.

The result showed that there is significant difference ( p= <0.001 ) in the annual DDE for group 1 with higher mean (M= 0.99 , SD= 1.24 ) than group 2 (M=0.65, SD= 0.85). The magnitude of the differences in the mean (mean difference= - 0.34, 95% CI : - 0.44 to - 0.24) was significant. Also, it showed that there is significant difference ( p= <0.001 ) in the annual skin doses for group 1 with higher mean (M= 0.97 , SD= 1.2 ) than group 2 (M=0.63, SD= 0.82). The magnitude of the differences in the mean (mean difference= - 0.34, 95% CI : - 0.44 to - 0.24) was significant. Moreover, the test’s result showed that there is significant difference ( p= <0.001 ) in the annual extremity doses for group 1 with higher mean (M= 8.74 , SD= 14.7 ) than group 2 (M=4.72, SD= 6.38). The magnitude of the differences in the mean (mean difference= - 4.02, 95% CI : - 5.28 to

– 2.76) was significant Figure 9, 10, and 11.

Figure 9: Annual exposure of the personal dose equivalents Hp(10) in mSv for the USN personnel working in NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT.

*The upper and lower whiskers represent the maximum and minimum values.

Figure 10: Annual exposure of the personal dose equivalents Hp(0.07), skin doses, in mSv for the USN personnel working NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT.

*The upper and lower whiskers represent the maximum and minimum values.

Figure 11: Annual exposure of the personal dose equivalents Hp(0.07), extremity doses, in mSv for the USN personnel working in NM facilities performing PET/CT vs. NM facilities that do not perform PET/CT.

*The upper and lower whiskers represent the maximum and minimum values.

CHAPTER 5. DISCUSSION

In our record of 528 and 285 USN NM workers assessed using the DT-702/PD and the DXT-RAD from 2003-2020, respectively, we observed a median annual radiation dose of 0.38 mSv (IQR, 0.05-1.27 mSv; mean, 0.82 mSv), 0.37 mSv (IQR, 0.06 – 1.22 mSv; mean = 0.80 mSv),

and 2.89 mSv (IQR = 0.76 – 7.86 mSv; mean = 6.65 mSv) for the DDE, skin doses and extremity doses, respectively. More than 95% of the annual DDE and skin doses were below three mSv: this is less than the average annual exposure from natural background radiation in the US. Almost 82% of the annual extremity doses were less than ten mSv. These values are significantly below the annual occupational limit of 50 mSv for the effective dose equivalent and 500 mSv for the dose equivalent to the skin and extremities established by the ICRP and recommended by the NRC. These DDE, skin doses, and extremity doses spread over a wide range, which could be related to the variability of NM workers’ occupations and tasks within NM departments.

Our study focuses on analyzing the data for the period when the occupational exposure of NM workers was expected to increase due to increased use of Tc-99m in myocardial studies, for instance, and decreased use of Tl-201 thallous chloride. This period also corresponded to the advent of PET/CT imaging, possibly leading to increased radiation exposure to the workers. However, the median value of annual personal dose equivalents (Hp(10)) appeared to be lower in our study (0.38 mSv in 2003 - 2020) than the median dose value for NM technologists working at civilian U.S. hospitals (2.07 mSv in 1979 - 2015) (15). Moreover, our result of the median annual DDE was lower than that of a recent study, including data from NM technologists working in civilian U.S. hospitals in 1980-2015 (1.2 mSv) (16). We computed summary statistics for easier comparison with other studies when excluding any annual dose below 0.03 mSv—the abovementioned studies recorded as minimal any annual dose below the LLD. After exclusion,

our dataset's median annual DDE was higher than without exclusion, with 0.62 mSv against 0.38 mSv, but still about half the median dose values from studies performed on workers from civilian hospitals. This result supports the hypothesis that the annual exposure to NM workers in the Navy is lower than to NM workers from civilian hospitals. These lower radiation doses to US Navy workers might be due to stringent radiation protection programs within the Navy. However, this dose difference could also be linked to a variation in workload between civilian and Navy hospitals. Our mean value of annual DDE was slightly lower than that of a cohort of 588 NM technologists from Saudi Arabia, monitored between 2015 and 2019, with 0.82 mSv against 1.22 mSv, respectively (51). Moreover, our mean annual DDE matched the estimated average annual effective dose to NM workers monitored worldwide in 1990-1994 (0.79 mSv). However, it was slightly higher than the estimated mean annual effective dose to general medical workers worldwide in 2000-2002 (0.70 mSv) (52).

To our knowledge, no published data reports annual occupational exposure to the skin and extremities for U.S. NM workers. Therefore, we only could compare skin doses from the present study with published skin doses from other countries. The mean annual skin dose in our study (0.80 mSv) was lower than the mean skin doses in Kuwait for NM technologists (0.94 mSv in 2009) and NM physicians (0.96 mSv in 2009) (53). Moreover, it was lower than the mean annual skin dose reported for 588 NM technologists in Saudi Arabia (1.23 mSv) in 2015-2019 (51).

On the other hand, the operational quantity for extremity doses was compared with the reported values in a study that evaluated the extremity exposure among NM workers in Serbia, using DXT-RAD finger ring (2010-2014) (54). The lowest mean annual value was recorded among radiographers in 2014 (12 mSv), thus almost twice the average annual value recorded in our study (6.65 mSv). It is recommended to wear ring dosimeters where the highest exposure is expected.

However, no information was provided on how workers wore their dosimeters in the present study, nor whether these recommendations were followed.

Because no information was available to identify NM facilities performing PET/CT in addition to general NM studies, we used the mailing addresses provided by the NDC and publicly available information from the Navy hospitals’ website to discriminate dose records for workers performing PET/CT procedures. Our results matched those from a recent study that showed an association of higher doses for NM technologists regularly performing PET/CT in the U.S. (16). The statistical analysis of doses to workers from facilities mentioning PET/CT on their website, compared with doses to workers from non-PET facilities, showed a statistically significant difference of mean annual dose between the two groups. However, in the absence of verified information on the regular performance of PET/CT procedures for each worker in our cohort, and due to the absence of a time specification on the implementation of PET in each facility, this result should be taken with caution when interpreting these results.

A major strength of this study is the consistency in the dosimeter type and the calibration method – using a single radiation protection program –, which prevents uncertainties related to variation in dosimetry practices. Moreover, previous studies conducted on occupational radiation exposure only included NM technologists. In contrast, the present study involves all possible workers from NM departments exposed to radiation, including NM technologists, physicians, nurses, and health/medical physicists: this means a more exhaustive evaluation of occupational exposure in NM departments. Lastly, our study is the first to report dose equivalents to the skin and extremities among NM workers in the US, and this type of data is now available for comparison with future studies.

A major limitation of this study is the absence of work history, such as the frequency of performed diagnostic and therapeutic procedures, the radionuclides in use, and the radiation safety procedures. The lack of such information limited our analysis of the dose results and trends. The absence of information on each worker's occupation or job title was a major inconvenience, making it very complex to separate dose analysis based on the occupation.

A second limitation is an assumption that doses recorded by the dosimeters reflect doses received by the workers. Based on the documentation obtained from the Navy’s radiation health protection program, the DT-702/PD dosimeter should be worn at the chest level to detect the exposure received by the body at the point where the highest exposure could occur (45). Some uncertainty arises from the obligation level each worker has toward these regulations. In addition, the data obtained from the NDC were doses per issued dosimeter. Due to overlap between years of some issued dosimeters, we recalculated doses by year, resulting in an over-or underestimation of some doses. The last limitation of our study is a common issue in radiation dosimetry: occupational exposure is assessed based on the personal dose equivalents, measured using personal dosimeters. These operational quantities are surrogates for the effective dose, which cannot be directly measured. However, report 160 from the European Commission of radiation protection on technical recommendations for monitoring individuals occupationally exposed to external radiation stated that the operational quantity Hp(10) generally overestimates the effective dose (55). Therefore, comparisons between personal dose equivalents and effective doses should be taken with caution.

Overall, a prospective study on the same group of workers or a simple survey could help

get the missing information in this study and better link the dose trends with the occupation, the workload, radiation safety program, and the performance of specific procedures such as

myocardial studies or PET/CT. A questionnaire has been drafted, and the dose analysis in the present study and could be used in future studies. It is provided as an Appendix.

CHAPTER 6. CONCLUSIONS

Nuclear medicine workers are exposed to protracted low-level radiation for extended periods, elevating their risk of breast cancer, SCC, and circulatory disease. Due to the possible risks from increased radiation exposure, the ICRP established recommendations to limit occupational doses and emphasized the ALARA principle. Previous studies conducted in the US to assess the trends of occupational exposure among NM workers included technologists from different medical institutions, which makes these studies susceptible to heterogeneity and measurement biases due to variations in work practices and radiation safety techniques between institutions. Although previous studies of occupational doses among the US radiologic technologists show that doses have decreased since 1939, which is likely due to improved radiation safety practices, a recent study of occupational doses among NM technologists in the US medical institutions showed that the maximum values of the annual personal dose equivalents among those workers generally increased from 1992 to 2015. Therefore, the present study was conducted to mitigate the problem of exposure heterogeneity within the study group and to test the hypothesis that NM workers' annual personal dose equivalents in USN medical centers are lower than the annual personal dose equivalents of NM workers from civilian medical centers across the United States due to a stringent radiation protection program within the USN.

Our study showed that the annual DDE, skin, and extremity doses of 528 and 285 NM

personnel working at the USN medical facilities and assessed using the DT-702/PD and the DXT- RAD from 2003-2020, respectively, were well below the annual occupational limits established by the ICRP (50 mSv for the total effective dose equivalents, and 500 mSv for the dose equivalents to the skin and extremities). The median annual DDE to NM workers in the USN is lower than NM workers from US civilian hospitals, supporting our hypothesis. Also, the mean value of annual

DDE was slightly lower than that for NM technologists from Saudi Arabia (2015-2019). Our study's mean annual skin dose was lower than the average for NM technologists andNM physicians in Kuwait and lower than for NM technologists in Saudi Arabia. The mean of annual DDE in the present study matched the estimated average annual effective dose to NM workers monitored worldwide (1990-1994), but slightly higher than the estimated mean annual effective dose to general medical workers worldwide (2000-2002).

Moreover, our study's mean annual extremity dose was half the lowest extremity exposure recorded among NM workers in Serbia. As expected, our mean annual exposure among workers in PET facilities was significantly higher than for non-PET facilities. The present study provided new data for future radiation monitoring among those workers and should help improve radiation protection programs in medical centers. We recommend a prospective data collection or a survey to provide detailed information on the USN workload and radiation protection programs for future studies.

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Table 1. Annual Occupational Dose Limits

Measurement Type

(a) ICRP- Dose Limit (mSv)

(b) NRC- Dose Limits

(mSv)

Total effective dose equivalent

20*

50

Lens equivalent dose

20**

150

Extremity equivalent dose

500

500

Shallow dose (Dose equivalent to the skin)

500

500

*Effective dose of 20 mSv/ year, averaged over five years with no single year exceeding 50 mSv

** This annual limit was lowered by ICRP in April 2011 from 150 mSv to 20 mSv, with the further provision that the dose should not exceed 50 mSv in any single year.

( Source: Reference 11. )

Table 2. Categories and corresponding definitions in the first dataset provided by the Navy Dosimetry Center, for DT-702/PD data.

Column

Definition

SDE_RPT

Shallow Dose Equivalent : the external exposure to the skin. The dose is equivalent at a tissue depth of 0.007 centimeters (cm) over an

area of 10 cm2.

PDE_RPT

Photon Dose Equivalent or what is referred to in the text as Deep

Dose Equivalent (DDE): the photon external whole-body exposure equivalent at a depth of 1 cm.

IndCode

Individual Code: anonymized codes assigned by the NDC to help identify each’s data.

Issue_Date

Date the dosimeter was issued to an individual. (Year Month Date)

Collect_Date

Date the dosimeter was collected from an individual. (Year Month Date)

CommAddr

Command Address : mailing address associated with the issued dosimeter.

( Name, City, State, Zip-Code)

Table 3. Categories and corresponding definitions in the second dataset provided by the Navy Dosimetry Center for DXT-RAD.

Column

Definition

EDE_RPT

Extremity Dose Equivalent: the extremity exposure measured using extremity dosimeter at tissue depth of 0.007 cm.

IndCode

See Table 2.

Issue_Date

See Table 2.

Collect_Date

See Table 2.

Occ_Code

See Table 2.

CommAddr

See Table 2.

Table 4. Several annual records in 2003–2020 used the DT-702/PD.

Year

Number of annual records

2003

152

2004

143

2005

159

2006

133

2007

112

2008

99

2009

92

2010

91

2011

80

2012

103

2013

111

2014

127

2015

117

2016

107

2017

115

2018

97

2019

41

2020

37

Table 5. A yearly number of annual records in 2003–2020, using the DXT-RAD.

Year

Number of annual records

2003

82

2004

100

2005

99

2006

76

2007

67

2008

63

2009

50

2010

46

2011

61

2012

82

2013

95

2014

92

2015

94

2016

95

2017

103

2018

80

2019

37

2020

35

Table 6. PET versus non-PET data, using the DT-702/PD.

PET

Non-PET

Number of facilities

2

14

Number of individuals

221

361

Number of annual records

787

1,207

Table 7. PET versus non-PET data, using the DXT-RAD.

PET

Non-PET

Number of facilities

2

13

Number of individuals

163

176

Number of annual records

600

800

Table 8. The number of observations, several workers, median, mean, Q1, Q3, and 95th percentiles, and the minimum to a maximum of various annual dose records for 2003-2020.

An

nual Dose Recor

ds (mSv)

# of

# of

Median

Mean

Q1

Q3

95th

Minimum

Annual Dose

Records

Workers

Percentile

to Maximum

Deep Dose

Equivalents

1,916

528

0.38

0.82

0.05

1.27

2.94

0.00-7.18

Skin Dose

Equivalents

1,916

528

0.37

0.80

0.06

1.22

2.86

0.00- 7.12

Extremity Dose

Equivalents

1,357

285

2.89

6.65

0.76

7.86

26.5

0.00-121

Table 9. Summary statistics of the annual dose records per year of the Hp(10).

Annual Dose Records (mSv)

Year

Median

Mean

Q1

Q3

Maximum

2003

0.35

0.60

0.06

0.87

3.46

2004

0.82

0.99

0.10

1.42

4.64

2005

0.61

0.96

0.07

1.43

5.51

2006

0.28

0.95

0.07

1.41

6.44

2007

0.35

0.95

0.04

1.23

6.50

2008

0.26

0.83

0.04

1.34

4.64

2009

0.20

0.84

0.06

1.23

4.80

2010

0.12

0.78

0.02

0.88

6.05

2011

0.59

0.96

0.09

1.46

4.36

2012

0.55

0.91

0.05

1.53

5.01

2013

0.48

0.79

0.07

1.32

3.27

2014

0.34

0.72

0.04

1.33

3.87

2015

0.28

0.85

0.05

1.35

7.18

2016

0.45

0.72

0.04

1.20

3.68

2017

0.29

0.77

0.05

1.30

6.26

2018

0.18

0.51

0.05

0.82

2.88

2019

0.43

0.77

0.07

1.51

2.87

2020

0.26

0.53

0.05

0.90

1.87

Table 10. Summary statistics of the annual dose records per year of the skin dose equivalents, the Hp(0.07).

Annual Dose Records (mSv)

Year

Median

Mean

Q1

Q3

Maximum

2003

0.37

0.60

0.06

0.84

3.65

2004

0.81

1.00

0.12

1.43

4.64

2005

0.55

0.90

0.06

1.33

5.36

2006

0.25

0.90

0.07

1.27

6.11

2007

0.35

0.95

0.04

1.24

6.47

2008

0.28

0.84

0.04

1.33

5.00

2009

0.22

0.83

0.06

1.2

4.73

2010

0.12

0.78

0.02

0.86

5.86

2011

0.56

0.92

0.08

1.40

4.38

2012

0.58

0.89

0.05

1.52

4.89

2013

0.43

0.77

0.08

1.24

3.12

2014

0.31

0.72

0.06

1.33

3.84

2015

0.30

0.84

0.06

1.50

7.12

2016

0.44

0.72

0.04

1.15

3.57

2017

0.30

0.73

0.05

1.20

6.12

2018

0.18

0.49

0.05

0.78

2.70

2019

0.42

0.75

0.07

1.36

2.77

2020

0.24

0.54

0.07

0.92

1.96

Table 11. Summary statistics of the annual dose records per year of the extremity dose equivalents, the Hp(0.07).

Annual Dose Records (mSv)

Year

Median

Mean

Q1

Q3

Maximum

2003

3.15

7.24

1.44

9.91

48.3

2004

4.57

10.1

2.15

11.3

68.8

2005

3.57

11.5

1.31

12.9

121

2006

4.45

9.28

1.42

10.1

92.3

2007

5.26

11.0

1.45

11.5

114

2008

3.73

7.31

1.10

8.05

48.7

2009

4.07

8.08

0.82

10.0

63.6

2010

3.23

7.88

0.84

6.47

53.8

2011

2.71

5.06

1.21

7.71

34.8

2012

3.95

7.59

0.93

12.3

42.4

2013

2.35

6.02

0.38

8.94

36.6

2014

1.34

5.07

0.23

5.65

59.8

2015

2.07

4.69

0.48

6.84

38.3

2016

2.13

3.78

0.61

5.32

27.1

2017

1.56

3.41

0.50

4.33

20.1

2018

1.42

3.04

0.39

4.31

21.3

2019

3.12

4.12

1.03

6.24

15.4

2020

1.49

2.62

0.74

3.51

12.7

Table 12. The workers, median, mean, Q1, Q3, and 95th percentiles and minimum to a maximum of the cumulative deep dose equivalents, skin dose equivalents, and extremity dose equivalents for 2003-2020.

Cumulative Dose Records (mSv)

# of workers

Median

Mean

Q1

Q3

95th

Minimum

to Maximum

a- Deep Dose Equivalents

528

0.39

2.96

0.05

3.18

14.22

0.00 - 46.6

b- Skin Dose Equivalents

528

0.39

2.90

0.05

3.08

14.39

0.00 - 44.3

c- Extremity Dose

Equivalents

285

13.0

31.64

2.89

38.51

134.10

0.11 - 529

Table 13. Table 13. Summary statistics of the personal dose equivalents the Hp(10) and Hp(0.07) for the PET facilities' skin and extremity records.

PET Facilities (mSv)

Median

Mean

Q1

Q3

95th

Maximum

Deep Dose

Equivalents

0.44

0.99

0.06

1.60

3.47

7.18

Skin Dose

Equivalents

0.42

0.97

0.06

1.58

3.40

7.12

Extremity Dose

Equivalents

3.16

8.74

0.73

9.51

37.2

121

Table 14. Summary statistics of the personal dose equivalents Hp(10) and Hp(0.07) for skin and extremity records in the non-PET facilities.

Non-PET Facilities (mSv)

Median

Mean

Q1

Q3

95th

Maximum

Deep Dose

Equivalents

0.29

0.65

0.06

0.95

2.38

6.13

Skin Dose

Equivalents

0.30

0.63

0.06

0.95

2.27

6.18

Extremity Dose

Equivalents

2.52

4.72

0.76

6.19

16.5

59.8

APPENDIX A

Summary statistics of the annual deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020

Percentiles

Smallest

1%

0

0

5%

.0053735

0

10%

.0149745

0

Obs

1,916

25%

.0548624

0

Sum of Wgt.

1,916

50%

.3754083

Mean

.8160365

75%

1.267237

Largest

6.259352

Std. Dev.

1.053848

90%

2.271212

6.439745

Variance

1.110597

95%

2.940099

6.49072

Skewness

1.939169

99%

4.558464

7.176692

Kurtosis

7.569551

APPENDIX B

Yearly summary statistics of the annual deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities

2003

Percentiles

Smallest

1%

0

0

5%

.0158069

0

10%

.0193887

.0017403

Obs

152

25%

.0558003

.0032977

Sum of Wgt.

152

50%

.3533911

Mean

.5954048

75%

.8666915

Largest

2.556723

Std. Dev.

.6878873

90%

1.557385

2.65008

Variance

.4731889

95%

2.237326

2.751594

Skewness

1.587392

99%

2.751594

3.45546

Kurtosis

5.384345

2004

Percentiles

Smallest

1%

.0012822

0

5%

.0106438

.0012822

10%

.0308526

.003324

Obs

143

25%

.1048888

.004826

Sum of Wgt.

143

50%

.8155563

Mean

.9941114

75%

1.423938

Largest

3.386387

Std. Dev.

.9653986

90%

2.361793

3.416775

Variance

.9319945

95%

2.84205

3.93676

Skewness

1.14879

99%

3.93676

4.63605

Kurtosis

4.045049

2005

Percentiles

Smallest

1%

.0012822

0

5%

.0106438

.0012822

10%

.0308526

.003324

Obs

143

25%

.1048888

.004826

Sum of Wgt.

143

50%

.8155563

Mean

.9941114

75%

1.423938

Largest

3.386387

Std. Dev.

.9653986

90%

2.361793

3.416775

Variance

.9319945

95%

2.84205

3.93676

Skewness

1.14879

99%

3.93676

4.63605

Kurtosis

4.045049

2006

Percentiles

Smallest

1%

.004466

.0036347

5%

.0203855

.004466

10%

.0342862

.0070844

Obs

133

25%

.0680952

.0101563

Sum of Wgt.

133

50%

.2762672

Mean

.9519001

75%

1.412995

Largest

4.144266

Std. Dev.

1.274838

90%

3.029637

4.187002

Variance

1.625213

95%

3.806939

4.257892

Skewness

1.655794

99%

4.257892

6.439745

Kurtosis

5.352752

2007

Percentiles

Smallest

1%

.0061564

.0049375

5%

.013367

.0061564

10%

.0194603

.0074532

Obs

112

25%

.0374651

.0085283

Sum of Wgt.

112

50%

.3508754

Mean

.9498236

75%

1.233454

Largest

5.223693

Std. Dev.

1.387288

90%

2.606879

5.88709

Variance

1.924567

95%

4.051319

6.130999

Skewness

2.145686

99%

6.130999

6.49072

Kurtosis

7.557846

2008

Percentiles

Smallest

1%

0

0

5%

0

0

10%

.0080472

0

Obs

99

25%

.0398241

0

Sum of Wgt.

99

50%

.261023

Mean

.8314757

75%

1.341586

Largest

3.732991

Std. Dev.

1.147634

90%

2.900131

3.970333

Variance

1.317064

95%

3.636149

4.168913

Skewness

1.592871

99%

4.635402

4.635402

Kurtosis

4.595665

2009

Percentiles

Smallest

1%

.0001528

.0001528

5%

.0046363

.0006318

10%

.0317041

.0006845

Obs

92

25%

.0611961

.0007781

Sum of Wgt.

92

50%

.1988361

Mean

.8411406

75%

1.234413

Largest

3.45946

Std. Dev.

1.135638

90%

2.563417

3.898583

Variance

1.289673

95%

3.302218

4.558464

Skewness

1.644283

99%

4.799671

4.799671

Kurtosis

5.069683

2010

Percentiles

Smallest

1%

.0003796

.0003796

5%

.0070811

.001003

10%

.009816

.0027117

Obs

91

25%

.0240745

.0050217

Sum of Wgt.

91

50%

.1151427

Mean

.7796714

75%

.8781401

Largest

3.858491

Std. Dev.

1.317878

90%

2.486832

5.077831

Variance

1.736803

95%

3.747566

5.798368

Skewness

2.240975

99%

6.049545

6.049545

Kurtosis

7.76719

2011

Percentiles

Smallest

1%

0

0

5%

.0053148

.0020422

10%

.0129835

.0030358

Obs

80

25%

.0885018

.0037949

Sum of Wgt.

80

50%

.5875151

Mean

.955201

75%

1.456991

Largest

3.442358

Std. Dev.

1.047137

90%

2.545557

3.555289

Variance

1.096496

95%

3.369639

4.103434

Skewness

1.395265

99%

4.355334

4.355334

Kurtosis

4.438917

2012

Percentiles

Smallest

1%

.0008358

0

5%

.0053168

.0008358

10%

.0122175

.0010657

Obs

103

25%

.0506676

.0015669

Sum of Wgt.

103

50%

.5462941

Mean

.910614

75%

1.528687

Largest

3.092861

Std. Dev.

1.021356

90%

2.121116

3.320576

Variance

1.043167

95%

2.716112

4.436441

Skewness

1.449513

99%

4.436441

5.005732

Kurtosis

5.332718

2013

Percentiles

Smallest

1%

0

0

5%

.0032804

0

10%

.0140443

0

Obs

111

25%

.0713282

.000541

Sum of Wgt.

111

50%

.4788338

Mean

.7891131

75%

1.321705

Largest

2.980606

Std. Dev.

.8829734

90%

2.038877

2.986499

Variance

.779642

95%

2.931366

3.244384

Skewness

1.20218

99%

3.244384

3.274509

Kurtosis

3.521907

2014

Percentiles

Smallest

1%

0

0

5%

.0041658

0

10%

.0140761

.0002244

Obs

127

25%

.0422195

.000234

Sum of Wgt.

127

50%

.3374017

Mean

.7205666

75%

1.334441

Largest

2.930588

Std. Dev.

.8674197

90%

1.917927

2.990605

Variance

.7524169

95%

2.398999

3.498989

Skewness

1.380122

99%

3.498989

3.872853

Kurtosis

4.334483

2015

Percentiles

Smallest

1%

.0009826

0

5%

.0050809

.0009826

10%

.011369

.0017945

Obs

117

25%

.0514741

.0040815

Sum of Wgt.

117

50%

.2835386

Mean

.8453923

75%

1.346161

Largest

3.547054

Std. Dev.

1.19854

90%

2.487023

4.048561

Variance

1.436498

95%

2.715241

5.767288

Skewness

2.382416

99%

5.767288

7.176692

Kurtosis

10.58892

2016

Percentiles

Smallest

1%

0

0

5%

.0007151

0

10%

.0044666

.0003958

Obs

107

25%

.0369615

.0004923

Sum of Wgt.

107

50%

.452927

Mean

.7210969

75%

1.195336

Largest

2.894889

Std. Dev.

.8832121

90%

1.925686

2.97426

Variance

.7800637

95%

2.841493

3.399453

Skewness

1.445903

99%

3.399453

3.678466

Kurtosis

4.389815

2017

Percentiles

Smallest

1%

.0020566

.0007266

5%

.0047266

.0020566

10%

.0094334

.002233

Obs

115

25%

.0459444

.003271

Sum of Wgt.

115

50%

.2865726

Mean

.7652477

75%

1.296422

Largest

3.422184

Std. Dev.

1.047726

90%

2.182504

3.560056

Variance

1.097731

95%

2.765138

3.959037

Skewness

2.150577

99%

3.959037

6.259352

Kurtosis

9.124552

2018

Percentiles

Smallest

1%

.0000456

.0000456

5%

.0004132

.0001181

10%

.0088668

.0001385

Obs

97

25%

.0500798

.0002033

Sum of Wgt.

97

50%

.1790895

Mean

.5077409

75%

.8227307

Largest

1.950156

Std. Dev.

.6401801

90%

1.560979

2.171966

Variance

.4098306

95%

1.887049

2.355326

Skewness

1.512951

99%

2.877304

2.877304

Kurtosis

4.711528

2019

Percentiles

Smallest

1%

.0079081

.0079081

5%

.0134662

.0097465

10%

.0211412

.0134662

Obs

41

25%

.0714212

.0137174

Sum of Wgt.

41

50%

.4256934

Mean

.7709586

75%

1.510869

Largest

2.18502

Std. Dev.

.8307606

90%

2.078768

2.313535

Variance

.6901632

95%

2.313535

2.337713

Skewness

.9017106

99%

2.870684

2.870684

Kurtosis

2.520716

2020

Percentiles

Smallest

1%

.0010885

.0010885

5%

.0066906

.0066906

10%

.0240003

.0081717

Obs

37

25%

.0511697

.0240003

Sum of Wgt.

37

50%

.2559418

Mean

.5342347

75%

.8983554

Largest

1.521588

Std. Dev.

.5847211

90%

1.521588

1.551218

Variance

.3418987

95%

1.698638

1.698638

Skewness

.9076189

99%

1.870278

1.870278

Kurtosis

2.378766

APPENDIX C

Summary statistics of the annual shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020

Percentiles

Smallest

1%

0

0

5%

.0070037

0

10%

.0182813

0

Obs

1,916

25%

.0556798

0

Sum of Wgt.

1,916

50%

.3725173

Mean

.7994701

75%

1.215276

Largest

6.119405

Std. Dev.

1.026777

90%

2.210767

6.181241

Variance

1.05427

95%

2.864718

6.473961

Skewness

1.968534

99%

4.635141

7.118781

Kurtosis

7.846537

APPENDIX D

Yearly summary statistics of the annual shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities

2003

Percentiles

Smallest

1%

0

0

5%

.0084649

0

10%

.0232357

.0034345

Obs

152

25%

.0619117

.0035827

Sum of Wgt.

152

50%

.3734783

Mean

.6024175

75%

.8353235

Largest

2.54432

Std. Dev.

.6952061

90%

1.607193

2.594654

Variance

.4833115

95%

2.239701

2.84054

Skewness

1.656896

99%

2.84054

3.64907

Kurtosis

5.817352

2004

Percentiles

Smallest

1%

0

0

5%

.0180982

0

10%

.0352173

0

Obs

143

25%

.1165865

.0004867

Sum of Wgt.

143

50%

.8086973

Mean

1.001939

75%

1.433539

Largest

3.395016

Std. Dev.

.9594585

90%

2.380001

3.553425

Variance

.9205606

95%

2.818681

3.887628

Skewness

1.125757

99%

3.887628

4.635141

Kurtosis

4.004581

2005

Percentiles

Smallest

1%

.0003918

0

5%

.0075263

.0003918

10%

.026471

.0004055

Obs

159

25%

.0558806

.0019618

Sum of Wgt.

159

50%

.5540211

Mean

.9012122

75%

1.335968

Largest

4.501707

Std. Dev.

1.115336

90%

2.477835

4.719437

Variance

1.243974

95%

3.467109

4.925521

Skewness

1.738235

99%

4.925521

5.361388

Kurtosis

5.993091

2006

Percentiles

Smallest

1%

.0038637

.0000145

5%

.0186963

.0038637

10%

.0384645

.0046722

Obs

133

25%

.0704271

.0118052

Sum of Wgt.

133

50%

.251845

Mean

.8992895

75%

1.267874

Largest

4.028935

Std. Dev.

1.205549

90%

2.887704

4.130642

Variance

1.453349

95%

3.45397

4.13113

Skewness

1.69271

99%

4.13113

6.117428

Kurtosis

5.526514

2007

Percentiles

Smallest

1%

.0045778

.000824

5%

.0098852

.0045778

10%

.0218932

.0059951

Obs

112

25%

.0369207

.0072682

Sum of Wgt.

112

50%

.3476557

Mean

.9470057

75%

1.244687

Largest

5.136432

Std. Dev.

1.386328

90%

2.608834

6.098285

Variance

1.921905

95%

3.781629

6.181241

Skewness

2.166295

99%

6.181241

6.473961

Kurtosis

7.734419

2008

Percentiles

Smallest

1%

0

0

5%

.0081023

.000813

10%

.0152435

.0048934

Obs

99

25%

.0398511

.0052773

Sum of Wgt.

99

50%

.2818285

Mean

.8394228

75%

1.329703

Largest

3.590305

Std. Dev.

1.167257

90%

2.842191

3.867624

Variance

1.362488

95%

3.585802

4.691899

Skewness

1.686533

99%

5.007534

5.007534

Kurtosis

5.143531

2009

Percentiles

Smallest

1%

0

0

5%

.0024876

0

10%

.0318315

0

Obs

92

25%

.0592

.0020215

Sum of Wgt.

92

50%

.2181594

Mean

.8260686

75%

1.19651

Largest

3.39449

Std. Dev.

1.120429

90%

2.543737

3.792108

Variance

1.255362

95%

3.215777

4.587036

Skewness

1.656993

99%

4.728184

4.728184

Kurtosis

5.130683

2010

Percentiles

Smallest

1%

0

0

5%

.0010832

0

10%

.0129185

.000339

Obs

91

25%

.0209081

.000655

Sum of Wgt.

91

50%

.1152964

Mean

.7778495

75%

.8557506

Largest

4.029578

Std. Dev.

1.308913

90%

2.380189

5.08658

Variance

1.713252

95%

3.853779

5.661973

Skewness

2.188447

99%

5.85675

5.85675

Kurtosis

7.424417

2011

Percentiles

Smallest

1%

0

0

5%

.006398

.0016755

10%

.0105388

.0033417

Obs

80

25%

.0819527

.0050043

Sum of Wgt.

80

50%

.5637543

Mean

.9188706

75%

1.399775

Largest

3.246475

Std. Dev.

1.015724

90%

2.454417

3.396849

Variance

1.031694

95%

3.12352

4.110482

Skewness

1.460607

99%

4.384409

4.384409

Kurtosis

4.76502

2012

Percentiles

Smallest

1%

.0008805

0

5%

.0103226

.0008805

10%

.0153127

.0027984

Obs

103

25%

.0469969

.005133

Sum of Wgt.

103

50%

.5842557

Mean

.8881484

75%

1.518886

Largest

3.005121

Std. Dev.

1.001568

90%

2.067253

3.184366

Variance

1.003139

95%

2.620567

4.789417

Skewness

1.564144

99%

4.789417

4.886204

Kurtosis

6.014499

2013

Percentiles

Smallest

1%

0

0

5%

.0036849

0

10%

.0163677

.0015644

Obs

111

25%

.0766911

.0015753

Sum of Wgt.

111

50%

.4301052

Mean

.7664876

75%

1.241447

Largest

2.896818

Std. Dev.

.844135

90%

2.01359

2.957707

Variance

.7125639

95%

2.76489

2.986268

Skewness

1.17474

99%

2.986268

3.119043

Kurtosis

3.423309

2014

Percentiles

Smallest

1%

.0003335

0

5%

.0111018

.0003335

10%

.0200854

.0003343

Obs

127

25%

.0565306

.00072

Sum of Wgt.

127

50%

.3108966

Mean

.7162428

75%

1.331176

Largest

2.864718

Std. Dev.

.8510828

90%

1.876407

2.91954

Variance

.7243419

95%

2.480283

3.45275

Skewness

1.362852

99%

3.45275

3.840094

Kurtosis

4.31162

2015

Percentiles

Smallest

1%

0

0

5%

.0056502

0

10%

.0143271

0

Obs

117

25%

.0594046

.0032522

Sum of Wgt.

117

50%

.3000902

Mean

.8405839

75%

1.49064

Largest

3.366111

Std. Dev.

1.158529

90%

2.349617

3.762578

Variance

1.342189

95%

2.660555

5.842677

Skewness

2.46023

99%

5.842677

7.118781

Kurtosis

11.57388

2016

Percentiles

Smallest

1%

.000943

.0005591

5%

.0043598

.000943

10%

.0104486

.0012348

Obs

107

25%

.0362867

.001927

Sum of Wgt.

107

50%

.4361207

Mean

.717801

75%

1.150011

Largest

2.811715

Std. Dev.

.8608956

90%

2.037004

2.833677

Variance

.7411413

95%

2.727755

3.376464

Skewness

1.404647

99%

3.376464

3.571377

Kurtosis

4.272691

2017

Percentiles

Smallest

1%

0

0

5%

.0065132

0

10%

.0132471

.0042236

Obs

115

25%

.0455055

.0057532

Sum of Wgt.

115

50%

.2939483

Mean

.7275742

75%

1.200172

Largest

3.24128

Std. Dev.

1.004895

90%

1.952452

3.502958

Variance

1.009813

95%

2.699834

3.965399

Skewness

2.28546

99%

3.965399

6.119405

Kurtosis

9.97769

( 72 )

2018

Percentiles

Smallest

1%

0

0

5%

.0002111

0

10%

.00628

5.68e-06

Obs

97

25%

.0478902

.0000862

Sum of Wgt.

97

50%

.1792101

Mean

.4868667

75%

.7786379

Largest

1.795226

Std. Dev.

.6123164

90%

1.571636

2.047335

Variance

.3749314

95%

1.752032

2.441648

Skewness

1.528986

99%

2.699398

2.699398

Kurtosis

4.777551

2019

Percentiles

Smallest

1%

.0028523

.0028523

5%

.0113948

.0110024

10%

.0343229

.0113948

Obs

41

25%

.0699882

.0257073

Sum of Wgt.

41

50%

.420664

Mean

.7523692

75%

1.356327

Largest

2.082096

Std. Dev.

.8038705

90%

2.04069

2.245001

Variance

.6462078

95%

2.245001

2.266349

Skewness

.9159093

99%

2.774321

2.774321

Kurtosis

2.541419

2020

Percentiles

Smallest

1%

.000199

.000199

5%

.0041498

.0041498

10%

.0242334

.0130043

Obs

37

25%

.0651802

.0242334

Sum of Wgt.

37

50%

.2393117

Mean

.5449339

75%

.9173883

Largest

1.578964

Std. Dev.

.6009547

90%

1.578964

1.619356

Variance

.3611466

95%

1.745904

1.745904

Skewness

.9475189

99%

1.961328

1.961328

Kurtosis

2.48645

APPENDIX E

Summary statistics of the annual shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities

Percentiles

Smallest

1%

.0217029

.0022509

5%

.1368456

.0030824

10%

.2482247

.0039535

Obs

1,357

25%

.7627603

.0039845

Sum of Wgt.

1,357

50%

2.88947

Mean

6.646006

75%

7.857769

Largest

77.51325

Std. Dev.

11.12562

90%

15.82636

92.3313

Variance

123.7794

95%

26.47331

114.2635

Skewness

4.206948

99%

59.76435

120.6773

Kurtosis

28.40237

( 73 )

APPENDIX F

Yearly summary statistics of the annual shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities

2003

Percentiles

Smallest

1%

.1100384

.1100384

5%

.3955024

.2269577

10%

.547952

.3153768

Obs

82

25%

1.443871

.3639799

Sum of Wgt.

82

50%

3.151708

Mean

7.236618

75%

9.913731

Largest

30.2099

Std. Dev.

9.158629

90%

18.51997

30.57057

Variance

83.88048

95%

29.75217

31.43298

Skewness

2.117284

99%

48.31822

48.31822

Kurtosis

7.800717

2004

Percentiles

Smallest

1%

.1592758

.1457507

5%

.3156808

.1728009

10%

.7206655

.1781174

Obs

100

25%

2.150729

.2141979

Sum of Wgt.

100

50%

4.572249

Mean

10.05775

75%

11.26102

Largest

52.39859

Std. Dev.

14.58192

90%

23.38075

60.15455

Variance

212.6323

95%

49.70239

64.61112

Skewness

2.492539

99%

66.71343

68.81573

Kurtosis

8.726595

2005

Percentiles

Smallest

1%

.0411071

.0411071

5%

.1988184

.0841144

10%

.3893005

.1151264

Obs

99

25%

1.308954

.1585269

Sum of Wgt.

99

50%

3.566083

Mean

11.52021

75%

12.86205

Largest

63.17491

Std. Dev.

19.31912

90%

30.22922

70.35617

Variance

373.2283

95%

60.81975

74.73264

Skewness

3.127999

99%

120.6773

120.6773

Kurtosis

14.27773

2006

Percentiles

Smallest

1%

.0633888

.0633888

5%

.2682183

.1158227

10%

.4955065

.1946463

Obs

76

25%

1.423433

.2682183

Sum of Wgt.

76

50%

4.453853

Mean

9.275897

75%

10.07067

Largest

33.65672

Std. Dev.

14.96471

90%

24.68233

35.90947

Variance

223.9426

95%

33.65672

74.88283

Skewness

3.611937

99%

92.3313

92.3313

Kurtosis

18.24488

2007

Percentiles

Smallest

1%

.0979249

.0979249

5%

.3140229

.1758117

10%

.4655808

.2421001

Obs

67

25%

1.445213

.3140229

Sum of Wgt.

67

50%

5.258824

Mean

11.02538

75%

11.53873

Largest

36.24613

Std. Dev.

18.22

90%

26.59136

43.48446

Variance

331.9683

95%

36.24613

77.51325

Skewness

3.65816

99%

114.2635

114.2635

Kurtosis

18.92618

2008

Percentiles

Smallest

1%

.0404472

.0404472

5%

.1100654

.075621

10%

.1668186

.0995994

Obs

63

25%

1.096516

.1100654

Sum of Wgt.

63

50%

3.728353

Mean

7.314512

75%

8.045874

Largest

31.75814

Std. Dev.

10.00344

90%

17.47653

32.47658

Variance

100.0689

95%

31.75814

40.23872

Skewness

2.328275

99%

48.65779

48.65779

Kurtosis

8.404312

2009

Percentiles

Smallest

1%

.0149458

.0149458

5%

.2620834

.091006

10%

.5227313

.2620834

Obs

50

25%

.8151155

.327626

Sum of Wgt.

50

50%

4.074058

Mean

8.077372

75%

9.955929

Largest

26.61095

Std. Dev.

12.48456

90%

20.92142

27.81606

Variance

155.8641

95%

27.81606

53.52279

Skewness

2.937633

99%

63.55399

63.55399

Kurtosis

12.15962

2010

Percentiles

Smallest

1%

.2067398

.2067398

5%

.2430426

.209037

10%

.3298148

.2430426

Obs

46

25%

.8380799

.271205

Sum of Wgt.

46

50%

3.228703

Mean

7.881159

75%

6.465068

Largest

30.45856

Std. Dev.

12.79693

90%

28.44971

40.62265

Variance

163.7614

95%

40.62265

50.89484

Skewness

2.422633

99%

53.8362

53.8362

Kurtosis

8.085803

2011

Percentiles

Smallest

1%

.0565581

.0565581

5%

.1538275

.1202071

10%

.3509958

.1516559

Obs

61

25%

1.209168

.1538275

Sum of Wgt.

61

50%

2.745102

Mean

5.060928

75%

7.709274

Largest

14.66929

Std. Dev.

5.981541

90%

10.47628

17.68077

Variance

35.77883

95%

14.66929

20.64693

Skewness

2.530651

99%

34.77391

34.77391

Kurtosis

11.77437

2012

Percentiles

Smallest

1%

.0140712

.0140712

5%

.1567765

.1003516

10%

.3125843

.1214804

Obs

82

25%

.9313893

.1472311

Sum of Wgt.

82

50%

3.952852

Mean

7.587485

75%

12.33601

Largest

29.93611

Std. Dev.

9.411401

90%

19.17125

30.04114

Variance

88.57448

95%

28.86268

42.21157

Skewness

1.807286

99%

42.42496

42.42496

Kurtosis

6.235459

2013

Percentiles

Smallest

1%

.0446474

.0446474

5%

.1099062

.0456403

10%

.1542054

.0667088

Obs

95

25%

.3843837

.1017152

Sum of Wgt.

95

50%

2.347798

Mean

6.024351

75%

8.939804

Largest

24.71736

Std. Dev.

8.073399

90%

16.54802

32.49219

Variance

65.17977

95%

21.61152

34.88761

Skewness

1.860972

99%

36.60241

36.60241

Kurtosis

6.328581

2014

Percentiles

Smallest

1%

.0078511

.0078511

5%

.0721064

.0268371

10%

.1169482

.0601499

Obs

92

25%

.2289982

.0614876

Sum of Wgt.

92

50%

1.376333

Mean

5.065321

75%

5.654953

Largest

28.87495

Std. Dev.

9.347452

90%

11.97626

33.22704

Variance

87.37487

95%

25.31287

40.4018

Skewness

3.461458

99%

59.76435

59.76435

Kurtosis

17.12187

2015

Percentiles

Smallest

1%

.083957

.083957

5%

.1347093

.1053502

10%

.1680737

.1099917

Obs

94

25%

.4778297

.1179634

Sum of Wgt.

94

50%

2.066357

Mean

4.687912

75%

6.83713

Largest

21.58343

Std. Dev.

6.455334

90%

10.69378

23.77067

Variance

41.67134

95%

18.08842

27.04418

Skewness

2.578411

99%

38.25689

38.25689

Kurtosis

11.37067

2016

Percentiles

Smallest

1%

.0127261

.0127261

5%

.1215181

.0170917

10%

.1840531

.0242604

Obs

95

25%

.6108225

.0443757

Sum of Wgt.

95

50%

2.127224

Mean

3.779112

75%

5.322699

Largest

14.35394

Std. Dev.

4.794174

90%

9.018718

19.57408

Variance

22.98411

95%

13.89317

19.86312

Skewness

2.329099

99%

27.05575

27.05575

Kurtosis

9.515051

2017

Percentiles

Smallest

1%

.1135154

.016183

5%

.1908533

.1135154

10%

.2781078

.1318665

Obs

103

25%

.5008725

.1502714

Sum of Wgt.

103

50%

1.563737

Mean

3.4084

75%

4.332285

Largest

16.53289

Std. Dev.

4.401668

90%

9.935368

16.76095

Variance

19.37468

95%

13.77273

18.6359

Skewness

1.963701

99%

18.6359

20.04729

Kurtosis

6.465768

( 78 )

2018

Percentiles

Smallest

1%

.0022509

.0022509

5%

.0079435

.0030824

10%

.1510461

.0039535

Obs

80

25%

.3947382

.0039845

Sum of Wgt.

80

50%

1.419367

Mean

3.04302

75%

4.308156

Largest

11.63484

Std. Dev.

3.76643

90%

8.480438

12.56597

Variance

14.18599

95%

10.68836

12.67641

Skewness

2.19236

99%

21.30811

21.30811

Kurtosis

9.132303

2019

Percentiles

Smallest

1%

.0119237

.0119237

5%

.0159467

.0159467

10%

.1066185

.0572418

Obs

37

25%

1.025548

.1066185

Sum of Wgt.

37

50%

3.116429

Mean

4.137128

75%

6.238679

Largest

10.62188

Std. Dev.

3.869094

90%

10.62188

11.3914

Variance

14.96989

95%

11.95496

11.95496

Skewness

1.052625

99%

15.37549

15.37549

Kurtosis

3.551712

2020

Percentiles

Smallest

1%

.0879792

.0879792

5%

.1268238

.1268238

10%

.2356016

.1519402

Obs

35

25%

.7384854

.2356016

Sum of Wgt.

35

50%

1.487486

Mean

2.616966

75%

3.513096

Largest

6.481418

Std. Dev.

3.101258

90%

6.481418

9.822086

Variance

9.6178

95%

10.20442

10.20442

Skewness

1.816878

99%

12.65337

12.65337

Kurtosis

5.564647

APPENDIX G

Summary statistics of the cumulative deep dose equivalents for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020

Percentiles

Smallest

1%

.0010657

0

5%

.0105749

0

10%

.0202651

0

Obs

528

25%

.0510137

0

Sum of Wgt.

528

50%

.385507

Mean

2.961223

75%

3.177992

Largest

35.69023

Std. Dev.

5.967875

90%

10.05622

43.95685

Variance

35.61553

95%

14.21984

44.11264

Skewness

3.719745

99%

29.33472

46.6182

Kurtosis

20.76875

( 80 )

APPENDIX H

Summary statistics of the cumulative shallow dose equivalents of the skin for 528 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020

Percentiles

Smallest

1%

.0032522

0

5%

.0135532

0

10%

.0207912

0

Obs

528

25%

.0511209

0

Sum of Wgt.

528

50%

.3863496

Mean

2.901108

75%

3.082477

Largest

34.54876

Std. Dev.

5.82575

90%

9.535597

43.16834

Variance

33.93936

95%

14.38533

43.27398

Skewness

3.697068

99%

28.47435

44.32508

Kurtosis

20.42743

APPENDIX I

Summary statistics of the cumulative shallow dose equivalents of the extremities for 285 nuclear medicine personnel working in the United States Navy medical facilities from 2003-2020

Percentiles

Smallest

1%

.1100384

.1052364

5%

.3404641

.1099062

10%

.6788423

.1100384

Obs

285

25%

2.889666

.1318665

Sum of Wgt.

285

50%

12.99507

Mean

31.64432

75%

38.50785

Largest

193.6166

Std. Dev.

56.06953

90%

82.82853

202.7736

Variance

3143.792

95%

134.0991

487.4695

Skewness

5.003586

99%

202.7736

528.6354

Kurtosis

38.91941

APPENDIX J

Summary statistics of the annual deep dose equivalents corresponding to 221 NM personnel working in USN medical facilities identified as PET facilities

Percentiles

Smallest

1%

0

0

5%

.002233

0

10%

.0094334

0

Obs

787

25%

.0552446

0

Sum of Wgt.

787

50%

.4414652

Mean

.9909822

75%

1.602285

Largest

6.259352

Std. Dev.

1.237229

90%

2.805705

6.439745

Variance

1.530736

95%

3.471585

6.49072

Skewness

1.651442

99%

5.253173

7.176692

Kurtosis

5.913189

APPENDIX K

Summary statistics of the shallow deep dose equivalents of the skin corresponding to 221 NM personnel working in USN medical facilities identified as PET facilities

Percentiles

Smallest

1%

0

0

5%

.0052731

0

10%

.0129185

0

Obs

787

25%

.0558806

0

Sum of Wgt.

787

50%

.4244372

Mean

.974075

75%

1.576345

Largest

6.117428

Std. Dev.

1.211676

90%

2.699954

6.119405

Variance

1.468158

95%

3.395016

6.473961

Skewness

1.670658

99%

5.136432

7.118781

Kurtosis

6.043804

APPENDIX L

Summary statistics of the shallow deep dose equivalents of the extremities corresponding to 163 NM personnel working in USN medical facilities identified as PET facilities

Percentiles

Smallest

1%

.0129868

.0022509

5%

.1224643

.0030824

10%

.2322271

.0039535

Obs

600

25%

.7295181

.0039845

Sum of Wgt.

600

50%

3.155826

Mean

8.740191

75%

9.51468

Largest

77.51325

Std. Dev.

14.68307

90%

23.83935

92.3313

Variance

215.5926

95%

37.1934

114.2635

Skewness

3.420971

99%

72.5444

120.6773

Kurtosis

18.26929

APPENDIX M

Summary statistics of the annual deep dose equivalents corresponding to 361 NM personnel working in USN medical facilities identified as non-PET facilities

Percentiles

Smallest

1%

.0004604

0

5%

.0088668

0

10%

.0201419

0

Obs

1,207

25%

.0552063

0

Sum of Wgt.

1,207

50%

.2865726

Mean

.6492319

75%

.9536016

Largest

5.005732

Std. Dev.

.8499088

90%

1.742694

5.507882

Variance

.722345

95%

2.381172

5.767288

Skewness

2.186277

99%

3.872853

6.130999

Kurtosis

9.328157

APPENDIX N

Summary statistics of the annual shallow dose equivalents of the skin corresponding to 361 NM personnel working in USN medical facilities identified as non-PET facilities

Percentiles

Smallest

1%

0

0

5%

.0101224

0

10%

.0212507

0

Obs

1,207

25%

.0556345

0

Sum of Wgt.

1,207

50%

.2956524

Mean

.6339584

75%

.9462707

Largest

4.789417

Std. Dev.

.8202126

90%

1.702806

5.361388

Variance

.6727487

95%

2.266349

5.842677

Skewness

2.210261

99%

3.781629

6.181241

Kurtosis

9.792458

APPENDIX O

Summary statistics of the annual shallow dose equivalents of the extremities corresponding to 176 NM personnel working in USN medical facilities identified as non-PET facilities

Percentiles

Smallest

1%

.0336422

.0119237

5%

.1502192

.0127261

10%

.2597432

.0149458

Obs

800

25%

.7570839

.0159467

Sum of Wgt.

800

50%

2.518783

Mean

4.718144

75%

6.193541

Largest

40.23872

Std. Dev.

6.379942

90%

11.98545

40.4018

Variance

40.70366

95%

16.49016

42.21157

Skewness

3.081133

99%

31.26666

59.76435

Kurtosis

16.93102

APPENDIX P

Two-sample t test’s result for the mean difference of the annual deep dose equivalents between non-PET and PET facilities

APPENDIX Q

Two-sample t test’s result for the mean difference of the annual shallow dose equivalents of the skin between non-PET and PET facilities

APPENDIX R

Two-sample t test’s result for the mean difference of the annual shallow dose equivalents of the extremities between non-PET and PET facilities

APPENDIX S

An example of a questionnaire could be used in future studies to help provide detailed information on the number of workers, workload, and radiation safety standards in the USN medical facilities.

Section One: General

This section will include general information on your nuclear medicine (NM) department.

Q1. Is your NM department located in the United States?

YES NO

Q2. How many NM technologists, physicians, nurses, and health/ medical physicists worked in your department in the following years?

Table #1

Year

# of NM Technologist

# of NM Physicians

# of Nurses

# of Health/Medical Physicist

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

Section Two: Diagnostic (non-PET)

This section will focus on your department's nuclear medicine (NM) diagnostic procedures. PET

procedures are not included.

Q1. Overall, how many diagnostic NM procedures were performed in your department in the following years?

Table #2

Year

# of diagnostic NM procedures

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

Q2. On average, how many diagnostic NM procedures are performed per week in your department?

Answer:

Q3. How many were cardiac NM procedures performed in your department in the following years?

Table #3

Year

# of cardiac NM procedures

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

Q4. Do you use Tc-99m to perform cardiovascular studies? If yes, in which year did you start using Tc-99m in your department?

YES NO Year :

Q5. Do you use Tl-201 to perform cardiovascular studies? If yes, in which year did you start using Tl-201 in your department?

( : )YES NO Year

Q6. Do you have CZT cameras for cardiac imaging?

YES NO

Section Three: Therapy

This section will focus on therapeutic nuclear medicine (NM) procedures performed in your

department. Please skip this section if your department does not perform therapeutic NM

procedures.

Q1. Overall, how many therapeutic NM procedures were performed in your department in the following years?

Table #4

Year

# of therapeutic NM procedures

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

Q2. On average, how many therapeutic NM procedures are performed per month in your department?

Answer:

Q3. Who is responsible for the preparation of radiopharmaceuticals for therapy?

NM Technologist

NM Physician

Other ………………

Q11. Who is responsible for the administration of radiopharmaceuticals for therapy?

NM Technologist

NM Physician

Other ………………

Section Four: PET

This section will focus on PET procedures. If your department does not perform PET procedures,

please skip this section.

Q1. When did you start performing PET or PET/CT procedures in your department?

Year:

Q2. Do you use a PET/CT camera?

YES NO

Q3. How many PET and PET/CT procedures did you perform in your NM department in the following years?

Table#5

Year

# of PET or PET/CT Procedures

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

Q4. Does your department require NM technologists to rotate between general NM and PET?

YES NO

Q5. Do you have Intego or any other PET infusion system?

YES NO

Q6. On average, how many PET procedures are performed per week in your department? Answer:

Section Five: Radiation Protection

This section will focus on radiation safety practices in your department.

Q1. How many body dosimeters are NM technologists required to wear in your department?

One Two

Q2. Where do NM workers usually wear the body dosimeter in your department?

Chest Level Other

Q3. Are NM physicians required to wear a body dosimeter?

YES NO

Q4. Are NM technologists required to wear a ring dosimeter?

YES NO

Q5. Are NM physicians required to wear a ring dosimeter?

YES NO

Q6. Are NM technologists required to wear a lead apron?

YES NO

Q7. Are NM technologists required to use a syringe shield during the manipulation of the radiopharmaceuticals?

YES NO

Q8. Are NM technologists required to use a syringe shield during the injection of the radiopharmaceuticals?

YES NO

Q9. Do you receive single doses of radiopharmaceuticals from radiopharmacy?

YES NO

Q10. How often are NM technologists, NM physicians, nurses, and health/medical physicists monitored in your department? (Please, use a to assign your answer in table #6).

Table#6

Title of the workers in the

NM department

Monthly

Quarterly

NM Technologists

NM Physicians

NM Nurses

Medical/Health physicists