Vijande Javier, Ballester Facundo, Ouhib Zoubir, Granero Domingo, Pujades-Claumarchirant M Carmen, Perez-Calatayud Jose
Department of Atomic, Molecular, and Nuclear Physics, University of Valencia, Burjassot, Spain.
Brachytherapy. 2012 Nov-Dec;11(6):528-35. doi: 10.1016/j.brachy.2011.11.005. Epub 2012 Jan 5.
The purpose of this work was to evaluate whether the delivered dose to the skin surface and at the prescription depth when using a Freiburg flap applicator is in agreement with the one predicted by the treatment planning system (TPS) using the TG-43 dose-calculation formalism.
Monte Carlo (MC) simulations and radiochromic film measurements have been performed to obtain dose distributions with the source located at the center of one of the spheres and between two spheres. Primary and scatter dose contributions were evaluated to understand the role played by the scatter component. A standard treatment plan was generated using MC- and TG-43-based TPS applying the superposition principle.
The MC model has been validated by performing additional simulations in the same conditions but transforming air and Freiburg flap materials into water to match TG-43 parameters. Both dose distributions differ less than 1%. Scatter defect compared with TG-43 data is up to 15% when the source is located at the center of the sphere and up to 25% when the source is between two spheres. Maximum deviations between TPS- and MC-based distributions are of 5%.
The deviations in the TG-43-based dose distributions for a standard treatment plan with respect to the MC dose distribution calculated taking into account the composition and shape of the applicator and the surrounding air are lower than 5%. Therefore, this study supports the validity of the TPS used in clinical practice.
本研究旨在评估使用弗莱堡瓣式施源器时皮肤表面及处方深度处的实际剂量是否与采用TG-43剂量计算形式的治疗计划系统（TPS）预测的剂量一致。
进行了蒙特卡罗（MC）模拟和放射变色胶片测量，以获取源位于其中一个球体中心以及两个球体之间时的剂量分布。评估了原发射线剂量贡献和散射剂量贡献，以了解散射分量所起的作用。使用基于MC和TG-43的TPS并应用叠加原理生成了标准治疗计划。
通过在相同条件下进行额外模拟，但将空气和弗莱堡瓣材料转换为水以匹配TG-43参数，对MC模型进行了验证。两种剂量分布的差异小于1%。与TG-43数据相比，当源位于球体中心时散射缺陷高达15%，当源位于两个球体之间时高达25%。基于TPS和基于MC的分布之间的最大偏差为5%。
考虑到施源器的组成和形状以及周围空气，基于TG-43的标准治疗计划剂量分布与计算得到的MC剂量分布之间的偏差低于5%。因此，本研究支持临床实践中使用的TPS的有效性。
