Henschke近接治療裝療管於商用治療計畫與蒙地卡羅方法間的劑量分布比較

A Comparison of Brachytherapy Treatment Planning System and Monte Carlo Dose Distribution in Henschke Applicator

游佩潔(Pei-Chieh Yu) ； 吳錦榕(Ching-Jung Wu) ； 雷德(Louis Tak Lui) ； 蕭世禎(Su-Zun Shaw) ； 粘心華(Hsin-Hua Nien)

《放射治療與腫瘤學》 19卷3期 (2012/09) Pp. 237-245

https://doi.org/10.6316/TRO/201219(3)237

摘要

目的：Henschke裝療管於近接治療造成的劑量擾動，在最近幾年內受到關注，為了瞭解劑量計算時有無含金屬遮蔽物，對於劑量影響程度，本研究將針對於Ir-192射源於水假體中的劑量分布，比較蒙地卡羅演算法及商用治療計量程式劑量分布結果。材料與方法：Henschke裝療管包含兩個半球體及一根垂直的管子，在此研究中可，Ir-192射源將被導入Henschke裝療管的三個通道中。其中兩個停留點分別位於兩個半球體各自的中心，第三個停留點位於此兩個半球體中心點的中間，此點為近接治療計畫及蒙地卡羅演算法的座標中心位置。取兩個半球體往外延伸0.5公分的邊界上六個點的平均劑量，作為歸一化的劑量點。本研究使用蒙地卡羅演算法作為劑量分布的模擬，而此演算法以網狀紀錄面（mesh tally）來執行劑量結果的輸出資料。為確保蒙地卡羅演算法參數設定之正確性，事先己與美國醫學物理學會第43工作小組（TG-43）所公佈的參數做比對。結果：在蒙地卡羅演算法和近接治療計畫的劑量圖中可以明顯的觀察到，有無Henschke裝療管的等劑量曲線分布的差異，經此等劑量曲線的比較可以知道Henschke裝療管明顯造成劑量曲線分布的不同，若Henschke裝療管被納入劑量計算的考量時，治療計畫劑量曲線由Z方向1.5公分往座標原點退至1公分處為蒙地卡羅等劑量曲線300 cGy。結論：Henschke裝療管造成的劑量擾動是有意義的，但此擾動只能以蒙地卡羅演算法的劑量圖表示，而近接治療計畫系統劑量圖無法呈現裝療管造成的劑量擾動。

關鍵字

蒙地卡羅 ； 近接治療

並列摘要

Introduction: In recent years, the dose perturbation caused by the Henschke applicator is a major concern in brachytherapy planning system (BPS). To investigate impact of the dose where there is a lack of metal shielding, Monte Carlo simulations, and BPS calculations have been performed for dose assessments in a Plastic Water® phantom.Material and Methods : A Henschke applicator consists of one tandem and two ovoids. In this study, an 192 Ir source would be driven into all three channels of a Henschke applicator, at the middle of each ovoid, and at the center of two ovoids. For BPS, the origin of the coordinates was set at the middle of two ovoids, as was the Monte Carlo simulation. The dose normalization point was the average dose at six arbitrary points extended to the surface of the ovoids by 5 mm. Monte Carlo N-Particle Transport Code MCNP (X-5 Monte Carlo Team) was used in this study to simulate the dose distribution and output simulation data was recorded by mesh tally. The Monte Carlo set-up parameters had been validated by TG-43 data in a previous report.Results: The isodose distribution with Henschke applicator and without Henschke applicator showed tremendous deviation between Monte Carlo simulation and BPS calculation. This indicated that a Henschke applicator affected the isodose distribution significantly. Compared to the prescription dose area, the simulation isodose curves had a shrinkage of about 0.5 cm, when the metal applicator was considered.Conclusions: The Henschke applicator affected the dose distribution significantly and this could be observed in Monte Carlo simulation, but not in BPS.

並列關鍵字

Monte Carlo ； Henschke applicator