Optimization of Position and Exposure Time of Radioactive Source in High-Dose-Rate Afterloading Brachytherapy

後荷式高劑量率輻射源暴露時間及位置最佳化之近接治療

趙良曉(Liung S. Chao) ； 顏上惠(Sang H. Yen) ； 李玉麟(Yuh L. Lee) ； 蕭正英(Cheng-Ying Shiau) ； 陳富都(Fu D. Chen) ； 陳光耀(Kuang Y. Chen)

《放射治療與腫瘤學》 2卷1期 (1995/03) Pp. 41-45

https://doi.org/10.6316/TRO/199502(1)41

摘要

後荷式高劑量率近接治療銥－九二單一射源，長3.5厘米，直徑1.1厘米，可遠距離程式化移動到預設的位置，在固定的時程內有2.5或5.0厘米兩種間距的移動方式。理論上對一固定治療方式射源位置及暴露時聞有無限多的排列方式。為獲得滿意的劑量曲線必須先決定最理想的射源位置及暴露時間的組合，可用線性方程組來計算，但大多數位置的暴露時問為負數值，本研究是發展一套數學方法計算射源數目位置及暴露時問的最佳組合，並且利用CMS治療計畫系統將劑量分佈畫出來，實際的考量則建立圓柱形劑量治療時間及位置表，劑量的誤差均在4%以內。進一步能計算單一平面三根插針近接治療，此原理能應用在更複雜的治療計畫。

關鍵字

後荷式高劑量率近接治療 ； 治療計畫 ； 最佳化

並列摘要

In the high-dose-rate afterloading brachytherapy unit, the 3.5 mm in length and 1.1 mm in diameter Ir-192 single source is remotely and programmably moved into thc preset positions which can be 2.5 or 5.0 mm apart for a certain period of time. Theoretically, there are infinite arrangements of position and exposure time of the radioactive source for a given treatment. In order to produce satisfactory isodose curves, the best number and allocation of the source position and exposure time must be predetermined. Optimization of number, location and exposure time of the source can be calculated involving linear equations. Unfortunately, by direct calculation the exposure time can be negative for some positions. In this study, a mathematical method is developed to calculate the number and proper positions of the source and the exposure time in each position, the dose distribution can be plotted out by a plotter of CMS treatment planning system, By this algorithm we match the dose requirement as clinically needed. For practical consideration, a table of source dwelling-time for cylindrical dose contour is constructed. The dose distributions were found to corresponding within 4% as initially requested. Furthermore, using the multiple linear equation one can determine the position and exposure time for up to three needles on single plane brachytherapy. This principles can be applied to more complicated treatment plannings.

並列關鍵字

Afterloading high-dose-rate ； brachytherapy ； Treatment planning ； Optimization