基於點射源視線模型的簡化法具有計算快速、簡單、直覺與易驗證的優點，在實務的屏蔽計算中最受歡迎。正確使用簡化法的關鍵是基於問題的射束/靶/屏蔽描述在文獻中挑選合適的射源項與衰減長度之屏蔽參數，或為問題建立特殊的屏蔽參數。然而，在質子治療加速器的屏蔽參數文獻中，本研究發現有許多彼此不太一致的屏蔽參數，造成使用者選擇的困難與不確定性；而重粒子治療加速器的屏蔽參數則是很不完整的，常常造成使用者只能選擇近似的屏蔽參數。若考慮自行建立屏蔽參數，則會面臨許多計算難題，如中子深穿透計算的誤差。另外，中子截面的選擇也是關鍵，尤其是在截面隨能量變化大的共振區。
有鑑於此，本研究採用經驗證可靠的射源與中子深穿透計算模型，考慮醫用加速器設施常用的射束/靶/屏蔽組合，有系統地擬合一系列以連續能量截面為主的蒙地卡羅法進行深穿透計算得到的劑量衰減曲線，以便分別得到適用於質子、重粒子(12C)治療加速器和加速器硼中子捕獲治療(AB-BNCT)設施的射源項與衰減長度等屏蔽參數，這應該是目前文獻上針對這些類型的加速器治療設施最完整可靠的屏蔽參數資料庫。在屏蔽參數應用的實例分析上，本研究考慮簡單幾何的單層與雙層屏蔽應用，以及常見質子、重粒子(12C)治療設施的屏蔽配置，採用簡化法與準確但複雜耗時的蒙地卡羅模擬相比，證明本研究所建立的屏蔽參數可適用於這些加速器設施的初期規劃與屏蔽分析。
關於AB-BNCT設施，本研究採用五種方法計算設施周邊的劑量率，其中，在蒙地卡羅法的計算中，以人造中子射源作為ADVANTG/MCNP5的射源項的計算效率最高。針對簡化法的使用，本研究建議將BSA納入射源項與衰減長度等屏蔽參數的產生，測試結果證明它能為設施的初期規劃提供一個快速且實用的估計。另外，AB-BNCT設施的實現需要一座電流輸出高達1 mA的質子加速器，它的運轉將伴隨大量二次中子，因此由中子引發的活化現象必須正視。基於一系列的FLUKA計算，本研究為此設施進行初步大範圍的物質活化分析，結果有利於未來優化細部設計和放射性廢棄物的管理。

關鍵字：質子與重粒子治療；加速器硼中子捕獲治療設施；屏蔽分析；蒙地卡羅模擬；簡化法；物質活化

Monte Carlo simulations are generally considered the most accurate method for complex accelerator shielding analysis. Simplified models based on a point-source line-of-sight approximation are often preferable in practice because they are intuitive and easy to use. A set of shielding data, including source terms and attenuation lengths for several common targets and shielding materials were generated by performing continuous-energy MCNP Monte Carlo simulations for 100–300 MeV protons and carbon ions with energies of 400 MeV, 430 MeV, and 800 MeV. Possible applications and a proper use of the data set were demonstrated through several simplified and practical cases, in which shielding analyses on typical proton and heavy-ion treatment rooms were conducted. A thorough and consistent comparison between the predictions of our point-source line-of-sight model and those obtained by Monte Carlo simulations for a 360° dose distribution around the room perimeter showed that the data set can yield fairly accurate or conservative estimates for the transmitted doses, except for those near the maze exit. In addition, our studies demonstrated that appropriate coupling between the generated source term and empirical formulae for radiation streaming can be used to predict a reasonable dose distribution along the maze. These case studies proved the effectiveness and advantage of applying the data set to a quick shielding design and dose evaluation for proton and heavy-ion accelerators.
This study also addressed methods that can be used in shielding analyses for a hypothetical accelerator-based boron neutron capture therapy (AB-BNCT) facility, which included an accelerator room and a patient treatment room. The epithermal neutron beam for BNCT purpose was generated by coupling a neutron production target with a specially designed beam shaping assembly (BSA), which was embedded in the partition wall between the two rooms. Neutrons were produced from a beryllium target bombarded by 1-mA 30-MeV protons. Several calculation methods were used to investigate this shielding problem, including analog and biased Monte Carlo simulations as well as a similar simplified model based on the specific BSA design. The advantages and disadvantages of these methods were discussed. In addition, material activation assessment of the proposed facility was performed using the FLUKA Monte Carlo code to quantify the magnitude of the problem in terms of the isotope inventories, induced activities, and residual dose rates. The predicted results were compared with the corresponding regulatory limits. Moreover, the effectiveness of various measures to reduce the impact of material activation was demonstrated.

Keywords: Proton and heavy-ion accelerators; Accelerator-based boron neutron capture therapy facility; Shielding analysis; Monte Carlo simulation; Simplified methods; Material activation

摘要 i
Abstract iii
誌謝 v
目錄 vi
表目錄 x
圖目錄 xi
第1章 導論 1
1.1 引言 1
1.2 文獻回顧 2
1.2.1 加速器的屏蔽計算 2
1.2.2 加速器的物質活化分析 11
1.3 研究動機 12
1.4 研究架構 16
第2章 計算機程式介紹 19
2.1 MCNP 19
2.2 FLUKA 23
第3章 質子治療加速器 26
3.1 驗證計算 26
3.1.1 中子產率 26
3.1.2 中子深穿透計算 28
3.2 屏蔽參數的生成 35
3.2.1 計算模型 35
3.2.2 中子產率 39
3.2.3 中子能譜與劑量衰減曲線 40
3.2.4 屏蔽參數 50
3.3 單層屏蔽的應用 53
3.4 雙層屏蔽的應用 56
3.5 典型治療室屏蔽分析的案例 63
3.5.1 設施的屏蔽配置 63
3.5.2 輻射場的特性 64
3.5.3 簡化法與蒙地卡羅法的比較 67
3.5.3.1 屏蔽外周邊劑量分布的比較 67
3.5.3.2 迷道劑量的探討 69
第4章 重粒子(12C)治療加速器 74
4.1 中子產率驗證計算 74
4.2 屏蔽參數的生成 77
4.2.1 計算模型 77
4.2.2 中子產率 79
4.2.3 中子能譜與劑量衰減曲線 80
4.2.4 屏蔽參數 87
4.3 典型治療室屏蔽分析的案例 92
4.3.1 設施的屏蔽配置 92
4.3.2 輻射場的特性 93
4.3.3 簡化法與蒙地卡羅法的比較 96
4.3.3.1 屏蔽外周邊劑量分布的比較 96
4.3.3.2 迷道劑量的探討 97
第5章 加速器硼中子捕獲治療設施 99
5.1 濾屏與AB-BNCT設施 99
5.2 驗證計算 100
5.2.1 中子產率 100
5.2.2 殘存劑量率 104
5.3 屏蔽計算 108
5.3.1 計算方法 108
5.3.1.1 方法(一) MCNP6直接計算 108
5.3.1.2 方法(二) 幾何分裂與俄羅斯輪盤 109
5.3.1.3 方法(三) SSW/SSR & 幾何分裂與俄羅斯盤 110
5.3.1.4 方法(四) ADVANTG/MCNP5 111
5.3.1.5 方法(五) 簡化法 116
5.3.2 設施輻射場的特性 119
5.3.3 計算效率的比較 126
5.3.4 屏蔽需求 131
5.4 物質活化分析 134
5.4.1 照射情節 134
5.4.1.1 第一種照射情節：30分鐘/一次照射 134
5.4.1.2 第二種照射情節：1年/連續照射 135
5.4.1.3 第三種照射情節：30年/連續照射 135
5.4.2 主要放射性同位素及其活度 137
5.4.2.1 鈹靶 138
5.4.2.2 BSA 139
5.4.2.3 混凝土 143
5.4.3 殘存劑量率與改善建議 145
5.4.4 放射性廢棄物豁免管制量的評估 149
第6章 結論與未來建議 152
6.1 結論 152
6.2 未來研究方向 158
6.2.1 簡化法在雙層屏蔽應用與探討 158
6.2.2 人造中子源的生成自動化 158
6.2.3 精進AB-BNCT設施物質活化的評估 159
參考文獻 160
附錄A 屏蔽參數的彙整 166
A.1 質子治療加速器 166
A.2 重粒子(12C)治療加速器 175
A.3 加速器硼中子捕獲治療設施 196
附錄B 屏蔽參數的應用案例 197
B.1 台大癌醫中心醫院輻質中心的劑量分析 (略) 197
B.2 林口長庚質子治療中心新增粒子束流實驗室的劑量分析 (略) 197
B.3台北醫學大學附設醫院質子治療中心的劑量分析 (略) 197
B.4 雙射源(質子、重粒子(12C))粒子治療設施的劑量分析 (略) 197
附錄C 論文發表 198

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