臺灣博碩士論文加值系統

直線加速器多葉式準直儀先天設計上的舌槽效應(tongue and groove effect)無法完全阻擋主射束，造成輻射滲漏現象。本研究中使用了Varian TrueBeam™相空間粒子檔案，於BEAMnrc蒙地卡羅程式建構Millennium120 MLC多葉式準直儀模組。模擬條件的改變包括使用不同能量，不同照野大小，不同量測深度下，以及不同的LINAC mode (flattening filter(FF) and flattening filter free (FFF)。相同的模擬條件下，亦使用底片測量此滲漏值。結果顯示，蒙地卡羅模擬之整體平均輻射滲漏率0.69% ± 0.04%，而量測值之整體平均輻射滲漏率1.60% ± 0.23%。相同條件下的模擬結果，滲漏率不會隨著能量的增加而增加。照野越大，平均輻射滲漏率越高。輻射滲漏率的現象隨著假體深度增加。無整平濾片的舌槽效應與有整平濾片相互比較，其滲漏率無顯著差異。

The tongue and groove design of the multi-leaf collimator (MLC) of the linear accelerator (LINAC) may result in the radiation leakage. In this study, the Varian TrueBeamTM phase space particle files were used to construct the Millennium 120 multi-leaf collimator module for Monte Carlo simulations of such tongue and groove effect. The simulations have been carried out in conditions of different energies, field sizes, depths, and two different LINAC modes, i.e., the flattening filter (FF) and the flattening filter free (FFF) modes. The leakages were also measured by the films for the specific conditions as used in the Monte Carlo simulations. The total average radiation leakage rates found by the Monte Carlo simulations and the measurements were 0.69% ± 0.04% and 1.60% ± 0.23% respectively. The leakage does not increase with energies. The average leakage increases with the filed sizes and depths. No significant differences in leakage rate of the tongue and groove effect were found between the FF and the FFF modes.

目錄
摘要 I
Abstract II
誌謝 III
目錄 IV
圖目錄 VI
表目錄 VIII
第一章 序論 9
1.1研究背景 9
1.2研究目的 10
1.3研究架構 10
第二章 文獻探討 11
2.1 OMAGA/BEAM 程式直線加速器模擬 11
2.2舌槽效應(tongue and groove effect) 12
2.3 Gafchromic EBT3放射自顯底片 16
第三章 材料與方法 18
3.1實驗流程圖 18
3.2直線加速器量測實驗方法 19
3.3 BEAM code 23
3.4.1 BEAMnrc模擬參數設定 24
3.4.2 DOSXYZnrc模擬參數設定 29
3.5多葉式準直儀構造 31
3.6 Gafchromic EBT3底片之特性探討 38
3.7底片劑量與光密度 39
第四章 結果與討論 41
4.1 EBT3底片臨床測量 45
4.2蒙地卡羅模擬結果 53
4.3討論 60
第五章 結論 78
參考文獻 80
附錄 83

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