目的：為增加以蒙地卡羅法進行強度調控放射治療模擬時的效率，本文以OMEGA/BEAM程式系統為基礎，建立一簡化之模擬程序，並加以驗證。材料與方法：不直接模擬多葉準直儀移動片段(segment)的細節，而是採用治療計畫系統所提供的fluence map作為權重(weighting)，修改開放照野下的相空間射源粒子(phase-space source particle)，使得由數個MLC移動片段所構成的照野可在一次蒙地卡羅模擬中運跑完成。其中我們修改了DOSXYZ程式，使其具備讀入fluence map以及調整相空間射源粒子權重等功能。結果與討論：在本文中所採用的簡化模擬程序首先針對MLC dynamic wedge案例進行驗證。針樹15、30、45與60度的MLC dynamic wedge，簡化的蒙地卡羅計算結果與實驗值(profiler)及治療計畫系統(CadPlan (上標 TM))吻合良好。該方法進一步針對五照野的腦瘤強度調控放射治療案例進行驗證，計算結果與底片量測及治療計畫系統的比較亦顯示吻合良好。結論：本文中所採用的強度調控放射治療簡化蒙地卡羅模擬程序可省略模擬MLC元件本身與其移動片段的細節等工作，其結果顯示與實驗值吻合良好，可大幅增加應用蒙地卡羅法於強度調控放射治療照野下效應的研究。

Purpose: To improve the efficiency of the Monte Carlo simulation on IMRT, the simplified method based on OMEGA/BEAM system was performed in this stud. Materials and Methods: Instead of modeling the detailed segments of MLC movements, the fluence map provided by the treatment planning system was applied to modify the weights of the phase-space source particles. Therefore, an IMRT portal comprised of several sub-fields could be condensed as a single field in the Monte Carlo simulation. The DOSXYZ code used in this study has bed modified with the capabilities of reading the fluence map file awl adjusting the weights of the phase-space particles correspondingly. Results and Discussion: The simplified method proposed ill this study was verified with the MLC dynamic wedge cases first. The calculated dose profiles of 15-, 30-, 45-, and 60-degree MLC dynamic wedge cases show good agreements with the measurements of the profiler and results of the treatment planning system. Furthermore, this method has also bed used to calculate a 5-portal brain tumor IMRT case and the results were compared with the film measurements and treatment planning system. Our results were generally in good agreement with the film and treatment planning system. Conclusion: The method of the simplified Monte Carlo simulation on IMRT described ill this study could save a lot of efforts on modeling the detailed segments of MLC movements and shows good agreement with measurements. It would be a good improvement of the efficiency and could be a simple and yet accurate method for applying Monte Carlo methods on the studies corresponding to the influences of IMRT in clinical tasks.