Title Page

Contents

ABSTRACT 18

CHAPTER I. INTRODUCTION 20

1.1. Computational Human Phantoms for Radiation Dosimetry 20

1.2. ICRP Adult Reference Computational Phantoms 26

1.3. Objectives of This Study 33

CHAPTER II. PHANTOM CONVERSION 35

2.1. General Organs and Tissues 36

2.2. Skeletal System 45

2.3. Small Intestine 56

2.4. Lymphatic Nodes 61

2.5. Eye and Lens 65

2.6. Blood in Large Vessels 72

2.7. Muscle 74

CHAPTER III. INCLUSION OF BLOOD CONTENT 76

3.1. Calculation of Mass, Density, and Elemental Composition of Organs and Tissues Inclusive of Blood content 77

3.2. Phantom Adjustment for Blood Inclusion 93

CHAPTER IV. INCLUSION OF THIN TARGET AND SOURCE REGIONS 100

4.1. Skin 101

4.2. Alimentary Tract System 104

4.3. Respiratory Tract System 110

CHAPTER V. MESH-TYPE ADULT REFERENCE COMPUTATIONAL PHANTOMS 119

5.1. General Phantom Characteristics 120

5.2. Geometric Similarity Comparison 142

5.2.1. Dice Index, Centroid Distance, and Hausdorff Distance 142

5.2.2. Organ Depth Distributions 145

5.2.3. Chord Length Distributions 159

5.3. Compatibility with Monte Carlo Codes 168

5.3.1. Monte Carlo Codes 168

5.3.2. Computation Time and Memory Usage 169

CHAPTER VI. DOSIMETRIC IMPACT 171

6.1. Monte Carlo Simulations with Geant4 172

6.2. External Exposure 174

6.2.1. Effective Dose Coefficients for Photon 174

6.2.2. Effective Dose Coefficients for Electron 192

6.2.3. Lens Dose Coefficients 210

6.3. Internal Exposure 215

6.3.1. Effective Doses per Radiation Emission for Photon 215

6.3.2. Effective Doses per Radiation Emission for Electron 233

6.3.3. Electron Specific Absorbed Fractions for Alimentary Tract System 251

6.3.4. Electron Specific Absorbed Fractions for Respiratory Tract System 260

CHAPTER VII. CONCLUSIONS AND FUTURE WORK 266

7.1. Summary and Conclusions 266

7.2. Suggestions for Future Work 269

REFERENCES 273

국문요지 278

Table 2.1. Dice index (DI), centroid distance (CD), and Hausdorff distance (HD)... 43

Table 2.2. Dice index (DI) and centroid distance (CD) comparing the converted... 55

Table 2.3. Nodal numbers and masses for the adult male and female of the UF/NCI family phantoms along with reference nodal... 64

Table 2.4. Numbers of polygonal facets, masses, and densities of the eye structures of the PM eye model constructed in the present... 70

Table 3.1. Masses of the organs and tissues for Reference Adult Male and... 80

Table 3.2. Elemental compositions and densities for organs and tissues exclusive of blood content for male 82

Table 3.3. Elemental compositions and densities for organs and tissues exclusive of blood content for female 84

Table 3.4. Elemental compositions and densities for organs and tissues inclusive of blood content for male 86

Table 3.5. Elemental compositions and densities for organs and tissues inclusive of blood content for female 88

Table 3.6. Mass data of the blood-inclusive bones of the mesh phantoms 90

Table 3.7. Elemental compositions and densities of the blood-inclusive bones of the mesh phantoms 91

Table 3.8. Dice index (DI), centroid distance (CD), and Hausdorff distance (HD)... 98

Table 4.1. Masses of source regions of alimentary tract organs of mesh phantoms... 108

Table 4.2. Target regions of alimentary tract organs of mesh phantoms and ICRP-... 109

Table 4.3. Length of the branches for each generation and their deviation from the reference value 117

Table 4.4. The target region of respiratory tract model of the mesh phantoms and ICRP-66 stylized models 118

Table 5.1. Organ/tissue masses of the mesh phantoms and the reference masses... 125

Table 5.2. Organ ID listing, medium, density, and mass of each organ/tissue for... 127

Table 5.3. List of media, their elemental compositions (percentage by mass), and their densities for the mesh-type male... 130

Table 5.4. List of media, their elemental compositions (percentage by mass), and their densities for the mesh-type female... 132

Table 5.5. List of source regions, their acronyms, and corresponding ID numbers... 134

Table 5.6. List of target regions, their acronyms, and corresponding ID numbers in... 137

Table 5.7. Dice index (DI), centroid distance (CD), and Hausdorff distance (HD)... 143

Figure 1.1. Stylized phantoms (a), voxel phantoms (b), and surface phantoms (c). 24

Figure 1.2. Mesh-type computational phantom in a polygonal-mesh format (left)... 25

Figure 1.3. ICRP-110 reference voxel phantoms: male (left) and female (right). 30

Figure 1.4. Skin and hollow organs (gall bladder wall, stomach wall, and urinary... 31

Figure 1.5. Eye and lens of ICRP-110 male reference phantom. 32

Figure 2.1. Conversion procedure for general organs and tissues. 40

Figure 2.2. Conversion procedure for large intestine. 41

Figure 2.3. Example of two objects for understanding geometrical similarity... 42

Figure 2.4. General organs and tissues of the mesh phantoms along with original voxel models for male (left) and female (right). 44

Figure 2.5. Conversion procedure for pelvis. 48

Figure 2.6. Adjustment of high-quality polygonal-mesh spine model to original voxel model. 49

Figure 2.7. Adjustment of the toe-standing feet of the ICRP-110 female phantom to become normal standing feet. 50

Figure 2.8. Density and effective atomic number for all substances of the ICRP-... 51

Figure 2.9. Sacrum of ICRP-110 reference voxel phantoms 52

Figure 2.10. Converted mesh model for male skeleton. 53

Figure 2.11. Converted mesh model for female skeleton. 54

Figure 2.12. Procedure for generation of small intestine model. 58

Figure 2.13. Flowchart of developed program to generate random small-intestine... 59

Figure 2.14. Generated mesh models for small intestine along with original voxel... 60

Figure 2.15. Flowchart of developed program to generate lymphatic nodes in the... 62

Figure 2.16. Frontal view of the lymph nodes of the mesh phantoms for the male... 63

Figure 2.17. Geometrical information of detailed eye model adapted by Behrens et... 67

Figure 2.18. Incorporation procedure of detailed eye model into the male phantom. 68

Figure 2.19. Mesh-type male phantom including the detailed eye model. 69

Figure 2.20. Dose deviation of constructed PM eye model from original stylized... 71

Figure 2.21. Blood in large vessels of the ICRP-110 phantoms (left) and the mesh phantoms (right). 73

Figure 2.22. Muscles of the mesh phantoms along with the original voxel models for the male (left) and female (right). 75

Figure 3.1. Female phantom before (left) and after (right) increase in liver volume... 95

Figure 3.2. Male phantom before (left) and after (right) adjustment for inclusion... 96

Figure 3.3. Female phantom before (left) and after (right) adjustment for inclusion... 97

Figure 4.1. Skin models of the mesh-type adult reference phantoms including the 50-㎛-thick target layer; the most outer skin... 102

Figure 4.2. Skin absorbed dose per fluence (pGy ㎠) of the mesh phantoms and... 103

Figure 4.3. Procedure to define target and source regions in the oral cavity of the male phantom. 106

Figure 4.4. Target and source regions defined in the alimentary tract system of the mesh-type male phantom: oral cavity (upper) and... 107

Figure 4.5. Target and source regions defined in the ET region of the male... 113

Figure 4.6. Flowchart of the developed program for generation of center lines of... 114

Figure 4.7. Inverted Y-shape model in the constructive solid geometry (CSG) format. 115

Figure 4.8. Lung voxel model (left) and lung PM model (right) for the male phantom. 116

Figure 5.1. Mesh-type adult reference phantoms for the male. 123

Figure 5.2. Mesh-type adult reference phantoms for the female. 124

Figure 5.3. Comparison of organs and tissues of the mesh-type male phantom with those of the ICRP-110 male phantom. 139

Figure 5.4. ICRP-110 female phantom (left) and mesh-type female phantom (right); muscle (blue green part), spongiosa (red... 140

Figure 5.5. Skeletal system of ICRP-110 female phantom (left) and mesh-type female phantom (right) viewed in the superior-... 141

Figure 5.6. Distribution of depth of 10 million randomly sampled points in the spongiosa below the body surfaces 146

Figure 5.7. Distribution of depth of 10 million randomly sampled points in the colon wall below the body surfaces 147

Figure 5.8. Distribution of depth of 10 million randomly sampled points in the lungs below the body surfaces 148

Figure 5.9. Distribution of depth of 10 million randomly sampled points in the stomach wall below the body surfaces 149

Figure 5.10. Distribution of depth of 10 million randomly sampled points in the breasts below the body surfaces 150

Figure 5.11. Distribution of depth of 10 million randomly sampled points in the gonads below the body surfaces 151

Figure 5.12. Distribution of depth of 10 million randomly sampled points in the urinary bladder wall below the body surfaces 152

Figure 5.13. Distribution of depth of 10 million randomly sampled points in the oesophagus below the body surfaces 153

Figure 5.14. Distribution of depth of 10 million randomly sampled points in the liver below the body surfaces 154

Figure 5.15. Distribution of depth of 10 million randomly sampled points in the thyroid below the body surfaces 155

Figure 5.16. Distribution of depth of 10 million randomly sampled points in the brain below the body surfaces 156

Figure 5.17. Distribution of depth of 10 million randomly sampled points in the salivary glands below the body surfaces 157

Figure 5.18. Distribution of depth of 10 million randomly sampled points in the skin below the body surfaces 158

Figure 5.19. Distribution of distances between 10 million randomly sampled point pairs in cortical bone (source region) and... 160

Figure 5.20. Distribution of distances between 10 million randomly sampled point pairs in cortical bone (source region) and... 161

Figure 5.21. Distribution of distances between 10 million randomly sampled point pairs in liver (source region) and spongiosa,... 162

Figure 5.22. Distribution of distances between 10 million randomly sampled point pairs in liver (source region) and urinary... 163

Figure 5.23. Distribution of distances between 10 million randomly sampled point pairs in lungs (source region) and spongiosa,... 164

Figure 5.24. Distribution of distances between 10 million randomly sampled point pairs in lungs (source region) and urinary... 165

Figure 5.25. Distribution of distances between 10 million randomly sampled point pairs in thyroid (source region) and... 166

Figure 5.26. Distribution of distances between 10 million randomly sampled point pairs in thyroid (source region) and urinary... 167

Figure 6.1. Dose coefficients (pGy ㎠) to the RBM for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 176

Figure 6.2. Dose coefficients (pGy ㎠) to the colon for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 177

Figure 6.3. Dose coefficients (pGy ㎠) to the lung for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 178

Figure 6.4. Dose coefficients (pGy ㎠) to the stomach for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 179

Figure 6.5. Dose coefficients (pGy ㎠) to the breast for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 180

Figure 6.6. Dose coefficients (pGy ㎠) to the remainder tissues for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO... 181

Figure 6.7. Dose coefficients (pGy ㎠) to the gonads for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 182

Figure 6.8. Dose coefficients (pGy ㎠) to the urinary bladder for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO... 183

Figure 6.9. Dose coefficients (pGy ㎠) to the oesophagus for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 184

Figure 6.10. Dose coefficients (pGy ㎠) to the liver for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 185

Figure 6.11. Dose coefficients (pGy ㎠) to the thyroid for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 186

Figure 6.12. Dose coefficients (pGy ㎠) to the endosteum for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 187

Figure 6.13. Dose coefficients (pGy ㎠) to the brain for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 188

Figure 6.14. Dose coefficients (pGy ㎠) to the salivary glands for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO... 189

Figure 6.15. Dose coefficients (pGy ㎠) to the skin for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 190

Figure 6.16. Effective dose coefficients (pSv ㎠) for photon exposures in AP, PA, LLAT, RLAT, ROT, and ISO geometries 191

Figure 6.17. Dose coefficients (pGy ㎠) to the RBM for electron exposures in AP,... 194

Figure 6.18. Dose coefficients (pGy ㎠) to the colon for electron exposures in AP,... 195

Figure 6.19. Dose coefficients (pGy ㎠) to the lungs for electron exposures in AP,... 196

Figure 6.20. Dose coefficients (pGy ㎠) to the stomach for electron exposures in... 197

Figure 6.21. Dose coefficients (pGy ㎠) to the breast for electron exposures in... 198

Figure 6.22. Dose coefficients (pGy ㎠) to the remainder tissues for electron... 199

Figure 6.23. Dose coefficients (pGy ㎠) to the gonads for electron exposures in... 200

Figure 6.24. Dose coefficients (pGy ㎠) to the urinary bladder for electron... 201

Figure 6.25. Dose coefficients (pGy ㎠) to the oesophagus for electron exposures... 202

Figure 6.26. Dose coefficients (pGy ㎠) to the liver for electron exposures in AP,... 203

Figure 6.27. Dose coefficients (pGy ㎠) to the thyroid for electron exposures in... 204

Figure 6.28. Dose coefficients (pGy ㎠) to the endosteum for electron exposures... 205

Figure 6.29. Dose coefficients (pGy ㎠) to the brain for electron exposures in AP,... 206

Figure 6.30. Dose coefficients (pGy ㎠) to the salivary glands for electron... 207

Figure 6.31. Dose coefficients (pGy ㎠) to the skin for electron exposures in AP,... 208

Figure 6.32. Effective dose coefficients (pSv ㎠) for electron exposures in AP,... 209

Figure 6.33. Lens dose coefficients (pGy ㎠) for photon exposures in AP, PA, LAT, ROT, and ISO geometries 213

Figure 6.34. Lens dose coefficients (pGy ㎠) for electron exposures in AP, PA,... 214

Figure 6.35. Specific absorbed fractions (㎏-1) to the RBM as target for photon...(이미지참조) 217

Figure 6.36. Specific absorbed fractions (㎏-1) to the colon as target for photon...(이미지참조) 218

Figure 6.37. Specific absorbed fractions (㎏-1) to the lungs as target for photon...(이미지참조) 219

Figure 6.38. Specific absorbed fractions (㎏-1) to the stomach as target for photon...(이미지참조) 220

Figure 6.39. Specific absorbed fractions (㎏-1) to the breasts as target for photon...(이미지참조) 221

Figure 6.40. Specific absorbed fractions (㎏-1) to the remainder tissues as target...(이미지참조) 222

Figure 6.41. Specific absorbed fractions (㎏-1) to the gonads as target for photon...(이미지참조) 223

Figure 6.42. Specific absorbed fractions (㎏-1) to the urinary bladder as target for...(이미지참조) 224

Figure 6.43. Specific absorbed fractions (㎏-1) to the oesophagus as target for...(이미지참조) 225

Figure 6.44. Specific absorbed fractions (㎏-1) to the liver as target for photon...(이미지참조) 226

Figure 6.45. Specific absorbed fractions (㎏-1) to the thyroid as target for photon...(이미지참조) 227

Figure 6.46. Specific absorbed fractions (㎏-1) to the endosteum as target for...(이미지참조) 228

Figure 6.47. Specific absorbed fractions (㎏-1) to the brain as target for photon...(이미지참조) 229

Figure 6.48. Specific absorbed fractions (㎏-1) to the salivary glands as target for...(이미지참조) 230

Figure 6.49. Specific absorbed fractions (㎏-1) to the skin as target for photon...(이미지참조) 231

Figure 6.50. Effective dose per radiation emission (pSv / #) for photon exposures... 232

Figure 6.51. Specific absorbed fractions (㎏-1) to the RBM as target for electron...(이미지참조) 235

Figure 6.52. Specific absorbed fractions (㎏-1) to the colon as target for electron...(이미지참조) 236

Figure 6.53. Specific absorbed fractions (㎏-1) to the lungs as target for electron...(이미지참조) 237

Figure 6.54. Specific absorbed fractions (㎏-1) to the stomach as target for electron...(이미지참조) 238

Figure 6.55. Specific absorbed fractions (㎏-1) to the breasts as target for electron...(이미지참조) 239

Figure 6.56. Specific absorbed fractions (㎏-1) to the remainder tissues as target...(이미지참조) 240

Figure 6.57. Specific absorbed fractions (㎏-1) to the gonads as target for electron...(이미지참조) 241

Figure 6.58. Specific absorbed fractions (㎏-1) to the urinary bladder as target for...(이미지참조) 242

Figure 6.59. Specific absorbed fractions (㎏-1) to the oesophagus as target for...(이미지참조) 243

Figure 6.60. Specific absorbed fractions (㎏-1) to the liver as target for electron...(이미지참조) 244

Figure 6.61. Specific absorbed fractions (㎏-1) to the thyroid as target for electron...(이미지참조) 245

Figure 6.62. Specific absorbed fractions (㎏-1) to the endosteum as target for...(이미지참조) 246

Figure 6.63. Specific absorbed fractions (㎏-1) to the brain as target for electron...(이미지참조) 247

Figure 6.64. Specific absorbed fractions (㎏-1) to the salivary glands as target for...(이미지참조) 248

Figure 6.65. Specific absorbed fractions (㎏-1) to the skin as target for electron...(이미지참조) 249

Figure 6.66. Effective dose per radiation emission (pSv / #) for electron exposures... 250

Figure 6.67. Specific absorbed fractions (g-1) to the oral mucosa for electron...(이미지참조) 255

Figure 6.68. Specific absorbed fractions (g-1) to the oesophagus for electron...(이미지참조) 256

Figure 6.69. Specific absorbed fractions (g-1) to the stomach for electron...(이미지참조) 257

Figure 6.70. Specific absorbed fractions (g-1) to the small intestine for electron...(이미지참조) 258

Figure 6.71. Specific absorbed fractions (g-1) to the colon for electron exposures within the mesh-type male phantom (▲), mesh-type...(이미지참조) 259

Figure 6.72. Specific absorbed fractions (g-1) to the ET region for electron...(이미지참조) 262

Figure 6.73. Specific absorbed fractions (g-1) to the BBbas for electron exposures...(이미지참조) 263

Figure 6.74. Specific absorbed fractions (g-1) to the BB sec for electron exposures...(이미지참조) 264

Figure 6.75. Specific absorbed fractions (g-1) to the bb bas for electron exposures...(이미지참조) 265

 국제방사선방호위원회(International Commission on Radiological Protection, ICRP)는 ICRP 110 간행물을 통해 기준 성인 남녀 전산 팬텀을 발표하였다. ICRP 기준 팬텀은 환자의 CT 영상을 기반으로 제작된 복셀(voxel) 팬텀이며, 이전 형태인 수학적 팬텀 보다 인체 내 해부학적 구조를 더욱 사실적으로 표현한다. 하지만, 기준 팬텀은 복셀 크기의 한계로 인해 수정체, 피부, 소화기 장기들과 같이 얇은 구조물을 정밀하게 표현하지 못하므로, 특히 투과력이 낮은 방사선에 대한 선량을 합리적으로 계산하지 못한다는 한계가 있다. 더욱이, 기준 팬텀은 호흡기 및 소화기 계통에 존재하는 8-40 마이크로미터 두께의 매우 얇은 방사선 민감층들을 표현하지 못하므로, ICRP에서는 기준 팬텀 대신에 별도로 수학적 모델을 이용하여 호흡기 및 소화기 계통에 대한 선량을 계산하고 있는 실정이다. 이러한 복셀형 ICRP 기준 팬텀의 문제점들을 해결하기 위해 본 연구에서는 새로운 형태인 메시형 기준 성인 남녀 전산 팬텀을 개발하였다. 새로운 메시 팬텀은 기존 복셀 팬텀을 고품질의 메시 모델로 변환하여 개발되었으며, 개발 과정에서 기준 복셀 팬텀이 지닌 여러 해부학적 문제점들을 개선하였다. 뿐만 아니라, 호흡기 및 소화기 계통에 존재하는 얇은 민감층들을 포함하여 유효 선량 계산에 필요한 모든 타겟(target) 및 선원(source) 영역을 팬텀에 정의하였다. 더욱이 새로운 팬텀은 혈액을 포함하는 ICRP 기준 장기 무게에 조정된 세계최초의 팬텀이다. 본 연구에서는 메시 팬텀을 Geant4 몬테칼로 방사선 수송 코드에 입력하여 외부 피폭 및 내부 피폭에 대한 선량 계수를 계산하고, 계산된 결과를 기존 기준 복셀 팬텀 및 수학적 모델을 이용하여 계산된 값과 비교하였다. 비교 결과, 메시 팬텀은 광자에 대해서 복셀 팬텀과 매우 유사한 선량을 제공하였으며, 유효 선량 차이는 외부 피폭 및 내부 피폭에 대하여 각각 대부분 3% 및 5% 이내였다. 반면에 전자에 대해서는 메시 팬텀은 기준 복셀 팬텀 및 수학적 모델과 매우 다른 선량 결과를 제공하였으며, 이러한 차이의 주된 요인은 메시 팬텀이 복셀 팬텀 및 수학적 모델의 한계점들을 극복하였기 때문이다. 이러한 결과를 비추어 볼 때, 새로운 메시 팬텀은 광자와 중성자와 같은 투과력이 좋은 방사선에 대해서는 기존 복셀형 기준 팬텀과 매우 유사한 선량 값을 제공하고, 베타선이나 알파선과 같은 투과력이 낮은 방사선에 대해서는 더욱 합리적이거나 알맞은 선량 값을 제공할 것으로 보인다. ICRP에서는 이미 본 연구 결과의 중요성을 인지하고, 본 연구에서 개발한 메시 팬텀을 차세대 ICRP 기준 성인 남녀 전산 팬텀으로 채택하기 위한 새로운 Task Group (즉, Task Group 103)을 결성하였다. 따라서, 본 연구 결과는 방사선량 측정 분야에서의 전산 팬텀에 대한 패러다임이 복셀 팬텀에서 메시 팬텀으로 변하는데 있어서 중요한 시발점이 될 것으로 기대된다.