thesis research thesis research on Health physics (CT scan research). follow the guidelines and write the thesis. TRENDS IN EXTERNAL RADIATION EXPOSURE AMO

thesis research on Health physics (CT scan research). follow the guidelines and write the thesis.

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

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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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10
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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 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 …

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