目的：探討使用不同直徑的圓柱狀裝療器、選擇不同的射源位置及最佳化劑量點，在作陰道近接治療計劃時對劑量分佈的影響。材料與方法：依據ABS（American Brachytherapy Society）報告，在使用圓柱狀裝療器施行近接治療時，建議採用陰道黏膜及黏膜下5.0 mm為表面及外側劑量評估點。評估劑量計算的因素有圓柱狀裝療器直徑的大小（1.5 cm vs. 3.5 cm）、改變射源點停留間距 （2.5, 5, 7.5, and 10 mm）及最佳化劑量點的安排，交叉分析其影響劑量分佈的結果。結果：直徑1.5 cm裝療器較直徑3.5 cm裝療器有較高的表面平均劑量（173.6 cGy vs.127.3 cGy），與較不均勻的劑量分佈（標準差31.8 cGy vs. 11.7 cGy）。在最佳化過程中，拉大最佳化劑量點間距（由2.5 mm至10.0 mm），直徑3.5 cm裝療器表面頂點劑量會增加28％。增加射源停留位置的間距，亦造成頂點劑量的增加。若改變最佳化劑量點的安排方式，外側頂點會高達70％的劑量增加。結論：臨床上若使用單管裝療器作陰道近接治療，直徑較大的圓柱狀裝療器可得到較均勻的劑量分佈。

Purpose : To evaluate the dose distribution of vaginal brachytherapy with different diameters of cylindrical applicator, source positions and optimized dose points. Materials and Methods : When using cylindrical applicator for vaginal brachytherapy, ABS (American Brachytherapy Society) recommended treatment report with the vaginal surface dose and the dose at 5 mm beneath mucosa. The affecting factors for dose optimization is this study include: diameter of vaginal cylinder, source positions and optimized dose points. Results : Vaginal applicator with smaller diameter (1.5 cm) has a higher average surface dose (173.6 cGy vs. 127.3 cGy) and a more inhomogeneous dose distribution (standard deviation 31.8 cGy vs. 11.7 cGy) than a larger one (3.5 cm). When the interval of optimized dose points was increasing to 10 mm, the dose at surface apex point increased 28% with the larger diameter applicator. Increasing interval of source dwelling positions resulted in a rise of dose at apex point. There was a 70% dose enhancement at off-surface dose point when optimized dose points were re-arranged. Conclusions : When utilizing single-channeled applicator for vaginal brachytherapy, a cylinder with larger diameter will result in more homogenous dose distribution.