目的：過去許多學者曾提出關於192Ir射源在水中的劑量分佈，但是對於一些組織密度不均勻的區域，如骨頭、鼻咽腔、支氣管及肺臟等部位則鮮有探討。本研究的主要目的即為探討192Ir射源在骨及肺組織中的劑量分佈。材料與方法：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。計算結果除了與過去其他學者的研究比較外，TLD測量也同時進行以便驗證蒙地卡羅模擬程式的準確性。結果：水中的計算結果與JF Williamson在1995年的結果相比誤差小於1.6%。而在骨組織中徑向劑量率（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。在肺組織則是相反的情況，徑向劑量率隨著深度降低情況明顯地比水中少。非均向函數在半徑較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。TLD測量結果在接近射源1-cm內時有較大誤差，而半徑3-cm以上的結果則相當符合EGS4模擬程式的計算結果。結論：本研究以EGS4模擬程式所計算出的水中的劑量參數與過去研究之差異小於2%，骨與肺組織中的計算值與TLD的驗證結果也相當符合。研究結果顯示，銥192射源在近接治療的劑量評估上仍有改善空間。本研究所模擬的狀況與實際臨床近接治療仍有一段差距，但不失為對銥192射源特性進一步了解的參考。

Purpose: Many authors have discussed radiation dose distributions of an192Ir source in Water. The purpose of our study is to analyze dose distribution of 192Ir in heterogeneity, such as bone and lung tissue, using Monte Carlo calculation and TLD measurements. Material and Methods : An EGS4 Monte Carlo simulation program, incorporating with detailed source construction, has been used to investigate the dose distribution in water, bone and lung phantoms. TLD measurements were also performed to verify the calculating accuracy. The small size (1mm x 1mm x 1mm cube) TLD-100H LiF dosimeter is chosen to minimize the influence of dose gradient in measurement. The compositions of bone and lung phantoms are referred to ICRU report 44. Results: The radial dose function and anisotropy function in water agree with published data in less than 1%. The radial dose function in bone decreases with depth much more than those in water and the difference can be up to 21%. In contrast, the dose distribution in lung shows less attenuation and scatter than in water and the difference can be up to 16%. The TLD measurements and Monte Carlo results agree within statistical uncertainty (approximately +/- 5%) when the radial distance is larger than 1 cm. At 0.5-cm radial distance, the extreme high dose gradient causes the measurement uncertainty to become too large to estimate the consistency. Conclusions: Most of previous studies focused on the dosimetry around an Iridium-192 in water. Through this study, we obtain a better understanding of the dose distributions in heterogeneities, bone and lung tissue.