臺灣博碩士論文加值系統

近接治療乃將小型放射源（如銥192、銫137）放入人體內部接近腫瘤處，或直接插入腫瘤中，以非常近的距離高劑量率照射腫瘤，在癌症治療上應用的相當廣泛。近年來更由於銥192射源及遙控後荷式治療機的發展，大幅提高近接治療的準確度。從腦部、鼻咽腔、支氣管、肺臟、腹腔、骨盆腔乃至於皮膚都是其應用範圍。
在劑量計算方面大部分還是假設射源周圍都是均勻的水，對於一些組織密度不均勻的區域，如鼻咽腔、支氣管及肺臟等部位可能會有錯估的現象。本研究針對目前臨床使用最廣泛的銥192射源，以蒙地卡羅模擬程式計算在水、骨和肺組織中的劑量分佈﹔水中的計算結果與過去其他學者的研究相當一致。而在骨組織中軸向劑量率(radial dose rate)則隨著深度降低的比水中多。在半徑0.1-12cm距離內骨組織與水中差異達21%。骨組織中非均向函數(anisotropy function)在較遠離射源處可能因散射線較水中為多而表現的較接近點射源。同理；在肺組織則是相反的情況，軸向劑量率隨著深度降低情況的比水中少。非均向函數在近處與水中沒有明顯差異，在半徑較遠處則與水中有明顯差異。熱發光劑量計(TLD)測量結果在近距離時與計算值有較大誤差，而半徑3 cm以上的測量則相當符合EGS4的計算結果。

Brachytherapy, consists of placing sealed radioactive sources very close to or in contact with the malignant tumor, has been widely used in the treatment of cancer for a long time. In recent years, the development of remote control after-loading machine has enhanced the accuracy of treatment delivery. Some clinical applications of brachytherapy, like the brain implant, nasopharyngeal intracavitary, intrabronchial insertion, and mold therapy, are increasingly used.
Most of previous studies focused on the dosimetry around an Iridium-192 in water. The purpose of our project is to analyze the dose distributions in heterogeneities phantom materials, like bone and lung. A Monte Carlo simulation has been used to calculate the dose distributions in water, bone and lung. The radial dose functions and anisotropy functions in water are in agreement with published data. The radial dose functions in bone decrease upon depth more than those in water, and the differences are ranging from 0 to 21%. In contrast, the dose distribution in lung shows less attenuation and scatters than that in water.
TLD measurements are also performed to verify the results of EGS4 simulation. The measurements and calculations are in agreement to each other where the radial distance is larger than 3 cm.

中文摘要...................................................3
ABSTRACT...................................................4
一、前言...................................................5
二、目的...................................................6
三、原理說明................................................8
3.1輻射與物質相互作用的物理理 ..............................8
A.光子與物質的相互作用 .....................................8
B.電子與物質的相互作用 ....................................15
3.2 EGS4蒙第卡羅模擬程式 ..................................18
A.蒙第卡羅法基本原理 ......................................18
B.亂數與取樣 ..............................................18
3.3近接治療射源的劑量計算公式 .............................21
3.4熱發光劑量術 ...........................................23
4.1 銥192射源蒙地卡羅程式模擬 .............................25
A. MAIN主程式 .............................................26
B. HOWFAR副程式 ...........................................31
C. AUSGAB副程式 ...........................................32
4.2 熱發光劑量計測量驗證 ..................................33
A. 劑量計的選擇與校正 .....................................33
B. 假體的選擇 .............................................34
C. 假體中測量 .............................................35
五、結果與討論 ............................................37
5.1過去的研究 .............................................37
5.2劑量分佈的比較 .........................................39
A. 蒙第卡羅法的計算結果 ...................................39
B. 熱發光劑量計測量結果 ...................................48
六、結論 ..................................................56
參考文獻 ..................................................58
附錄一：RANDOM NUMBER GENERATOR BY MARSAGLIA AND ZAMAN ....60
附錄二：銥192射源在水中的模擬程式 .........................63
附錄三：銥192射源在水-空氣假體中的模擬程式 ................72
附錄四：TLD重複性測試結果 .................................82
附錄五：TLD劑量特性曲線校正結果 ...........................85

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