Avoidable Occupational Medical Radiation and Dose Constraints, Focusing on PET/CT Imaging = PET/CT 영상 검사를 중심으로 회피가능한 직업적 의료방사선과 선량제약치

다국어 초록 (Multilingual Abstract)

State-of-the-art PET/CT systems provide the significant advantage of seamlessly integrating functional nuclear medicine images with anatomical information on a single-modality system. This is achieved by performing PET and CT scans consecutively, without requiring the patient to change position. The fused images offer a comprehensive diagnostic perspective, combining the functional details from PET with the anatomical clarity of CT. The typical PET/CT acquisition process involves sequential steps: CT scout, CT imaging (which takes less than 30 seconds), followed by PET imaging, which takes typically 15 to 30 minutes. However, the time gap between the PET imaging and CT imaging can result in misregistration in fused PET/CT images due to patient movement. Patient-induced movement artifacts, primarily caused by motion during the scan, it’s significantly affect the quality of the PET/CT images, potentially leading to inaccurate diagnoses and negatively impacting the patient's treatment plan. Moreover, if re-examination is required, this not only increase radiation exposure for the patient but also poses additional risks to the PET/CT related staffs.
This dissertation aimed to analyze motion artifacts that occur during the PET/CT examinations and evaluate radiation exposure data from the past five years of radiation workers in various radiation environments within the nuclear medicine department. Additionally, we investigates the radiation exposure experienced by radiotechnologists and related staffs during the complete PET and PET/CT examination process, and then we propose “Dose Constraints“ in our nuclear medicine situations. This analysis is supported by a meta-analysis of global research literature from the recent 23 years, providing a comprehensive understanding of radiation exposure in these settings.
In Chapter 3, we conducted a retrospective study in which data from over 2,600 patients were initially collected from the largest medical center in Songpa-gu, Seoul, Republic of Korea. By the study criteria, finally 977 patients data were analyzed. The results showed that the most common motion artifact(image misregistration between PET and CT) during 18F-FDG PET/CT imaging were caused by urine accumulation in the bladder and movement around head area. Additionally, analyzing the differences in movement type based on the patient's gender, age, and scan duration, it was found that the incidence of motion artifacts was higher in men than in women, and the frequency of motion increased as the examination time more required. In terms of movement characteristics, bladder-related motion artifacts were the most frequent and severe in both men and women. Furthermore, a statistically significant difference in movement type was observed based on patient's arm position(Arm-up;Arm-down) and scan direction(Caudocranial;Craniocaudal). Specifically, when the arms were positioned up, the most common motion artifact was caused by head movement. Conversely, when the arms were positioned down, bladder-related artifacts was more prominent than head movement artifacts. Regarding scan direction, there was a statistically significant difference in bladder-related artifacts between Caudocranial and Craniocaudal direction, with bladder-related artifacts being the most frequent type of motion in both adult men and women. These findings underscore the critical impact of patient positioning and scan direction on motion artifacts, particularly in relation to urine accumulation in the bladder.
In Chapter 4, we investigated the annual and 5 years cumulative radiation exposure doses (RED) of occupational radiation workers (radiotechnologist, clinical pathologists, doctors, nurses, and other(administrative staff)) at the Department of Nuclear Medicine in the same hospital from 2016 to 2020. During the data collection period, initially, 125 radiation workers were recruited, at last, finally 96 radiation workers being included in this study. The results reveal that the radiation exposure peaked in 2019, and the averaged radiation exposure has steadily increased since then. Notably, two radiologists exceeded the quarterly exposure limits of 5 mSv in 2019. Additionally, analyzing the differences by occupation, “radiotechnologists” were found to have significantly higher radiation exposure, up to 11 times more than “others“ occupational group over the five-year period (p<.001). Furthermore, analyzing differences based on workplace, those working in General (Gamma) and PET/Cyclotron workplace experienced up to 11 times higher radiation exposure compared to ”others” workplace over the same period (p < 0.001). Based on the above results, we propose dose constraints value in our Nuclear Medicine situations; 7 mSv/yr(or max. 15 mSv/yr) and 35 mSv/5yrs.
In Chapter 5, we conducted a meta-analysis to evaluate the radiation exposure dose experienced by radiological staffs during the entire PET and PET/CT examination process. A comprehensive search was performed using PubMed, Medline, and EMBASE, resulting in the inclusion of 15 studies comprising 30 cases in the analysis. The results indicate that radiation exposure during PET/CT examinations has decreased significantly over time, with a significant difference observed when comparing inadequately shielded(Unshielded) and adequately shielded(Shielded) environments during radiopharmaceutical administration, and particularly since the introduction of the dose reduction paradigm in 2010, a greater reduction in radiation exposure has been observed. And additionally, we identified a statistically significant difference in radiation exposure based on the location of the study, highlighting geographical variations in safety practices and exposure levels. In total, we found that the average radiation exposure during the entire 18F-FDG PET/CT procedure since 2010 was 9.29 uSv/GBq.
In this study, we identified the occurrence of movement artifacts in patients during PET/CT examinations and the radiation exposure experienced by both patients and radiation worker in nuclear medicine field through a retrospective cohort analysis. Additionally, we conducted a meta-analysis to comprehensively examine whether radiation exposure to PET/CT related radiation workers has decreased over the past several decades and to explore the relationship between shielding surrounding also dose reduction paradigms and radiation exposure. Furthermore, We propose the levels of Dose Constraints in nuclear medicine radiation worker based on the 5 years real exposure data.

목차 (Table of Contents)

• Abstract 4
• Contents i
• List of Tables vi
• List of Figures xi
• Chapter 1. Introduction
• 1.1. Background 1
• 1.2. Research Objectives 6
• 1.3. Method and Structure 8
• Chapter 2. Review
• 2.1. PET(Positron Emission Tomography) System 10
• 2.1.1. PET tracer 10
• 2.1.2. PET 11
• 2.1.3. Attenuation 16
• 2.1.4. PET imaging modes 18
• 2.1.5. CT imaging parameters and dosimetry 20
• 2.1.6. Dual modality PET/CT 23
• 2.2. Motion Artifact 28
• 2.2.1. Head motion 29
• 2.2.2. Arm motion 31
• 2.2.3. Bladder and organs motion 33
• 2.2.4. Organs(Respiratory, Breathing) motion artifact 35
• 2.3. Medical Radiation 43
• 2.3.1. PET with radiation exposure in medical use 43
• 2.3.2. Radiation worker / Radiation related worker 50
• Chapter 3. Analysis of Motion Artifacts during 18F-FDG PET/CT Imaging
• 3.1. Introduction 54
• 3.2. Motion Artifacts Analysis 57
• 3.2.1. Subjects 57
• 3.2.2. 18F-FDG PET/CT imaging 57
• 3.2.3. Analysis of data 58
• 3.3. Results 59
• 3.3.1. Characteristics of patients 59
• 3.3.2. Difference in motion artifacts by age 61
• 3.3.3. Difference in motion artifacts by arm position 63
• 3.3.4. Difference in motion artifacts by scan direction 67
• 3.3.5. Difference in motion artifacts by scan time required and multiple factors 72
• 3.4. Discussion 83
• Chapter 4. Cumulative Radiation Dose in Nuclear Medicine Worker
• 4.1. Introduction 93
• 4.2. Method 97
• 4.2.1. Subjects 97
• 4.2.2. Analysis 97
• 4.3. Results 98
• 4.3.1. Characteristics of radiation worker 98
• 4.3.2. Analysis of the radiation exposure dose by gender and age 100
• 4.3.3. Analysis of the radiation exposure dose by occupation and workplace 107
• 4.3.4. Analysis of the radiation exposure dose by multiple factors 113
• 4.3.5. The results of linear regression analysis 119
• 4.4. Discussion 122
• Chapter 5. Meta-Analysis of Radiation Exposure among Medical Staffs during PET/CT Process
• 5.1. Introduction 130
• 5.2. Method 132
• 5.2.1. Search strategy 132
• 5.2.2. Study quality assessment 133
• 5.2.3. Statistical analysis 135
• 5.3. Results 141
• 5.3.1. Data extraction 141
• 5.3.2. Characteristics of the studies 143
• 5.3.3. Study quality 146
• 5.3.4. Whole body exposure dose 148
• 5.3.5. Location of study 164
• 5.3.6. Before and after 2010(Dose reduction paradigm) 167
• 5.4. Discussion 174
• Chapter 6. Summary and Overall Conclusions
• 6.1. Limitations 178
• 5.2. Summary and Conclusions 180
• References 187
• Abbreviations 200
• 국문 초록 202