Medical Physics Laboratory, Medical School, University of Athens, 75 Mikras Asias, 115 27 Athens, Greece.
Med Phys. 2010 Feb;37(2):649-61. doi: 10.1118/1.3290630.
The aim of this work is to validate a deterministic radiation transport based treatment planning system (TPS) for single 192Ir brachytherapy source dosimetry in homogeneous water geometries.
TPS results were obtained using the deterministic radiation transport option of a BRACHYVISION v. 8.8 system for three characteristic source designs (VS2000, GMPlus HDR, and GMPlus PDR) with each source either centered in a 15 cm radius spherical water phantom, or positioned at varying distance away from the phantom center. Corresponding MC simulations were performed using the MCNPX code v.2.5.0 and source geometry models prepared using information provided by the manufacturers.
Comparison in terms of the AAPM TG-43 dosimetric formalism quantities, as well as dose rate distributions per unit air kerma strength with a spatial resolution of 0.1 cm, yielded close agreement between TPS and MC results for the sources centered in the phantom. Besides some regions close to the source longitudinal axes where discrepancies could be characterized as systematic, overall agreement for all three sources studied is comparable to the statistical (type A) uncertainty of MC simulations (1% at the majority of points in the geometry increasing to 2%-3% at points lying both away from the source center and close to the source longitudinal axis). A corresponding good agreement was also found between TPS and MC results for the sources positioned away from the phantom center.
Results of this work attest the capability of the TPS to accurately account for the scatter conditions regardless of the size or shape of a given geometry of dosimetric interest, and the position of a source within it. This is important since, as shown in the literature and summarized also in this work, these factors could introduce a significant dosimetric effect that is currently ignored in clinical treatment planning. It is concluded that the implementation of the deterministic radiation transport option of the BRACHYVISION v. 8.8 system for 192Ir brachytherapy dosimetry in homogeneous water geometries yields results of comparable accuracy to the golden standard of Monte Carlo simulation, in clinically viable calculation times.
本工作旨在验证基于确定性辐射传输的治疗计划系统（TPS）在同质水几何中用于单 192Ir 近距离治疗源剂量学的准确性。
使用 BRACHYVISION v. 8.8 系统的确定性辐射传输选项，针对三种典型源设计（VS2000、GMPlus HDR 和 GMPlus PDR）获得 TPS 结果，每个源要么位于 15cm 半径球形水模体的中心，要么位于离模体中心不同距离处。使用 MCNPX 代码 v.2.5.0 进行相应的 MC 模拟，并使用制造商提供的信息准备源几何模型。
以 AAPM TG-43 剂量学形式为量度，以及单位空气比释动能率的剂量率分布（空间分辨率为 0.1cm），与 TPS 和 MC 结果进行比较，结果表明，对于位于模体中心的源，两者之间具有很好的一致性。除了在源纵轴附近的一些区域可能存在系统误差外，对于所研究的所有三种源，总体一致性与 MC 模拟的统计（A 类）不确定性相当（在几何形状的大多数点上为 1%，在远离源中心和靠近源纵轴的点上增加到 2%-3%）。对于位于离模体中心较远的源，也发现 TPS 和 MC 结果之间具有良好的一致性。
这项工作的结果证明了 TPS 能够准确地考虑散射条件，而与感兴趣的剂量学几何形状的大小或形状以及源在其中的位置无关。这一点很重要，因为正如文献中所示并在本工作中也进行了总结，这些因素可能会引入显著的剂量学效应，而目前在临床治疗计划中忽略了这些效应。因此，可以得出结论，在同质水几何中用于 192Ir 近距离治疗剂量学的 BRACHYVISION v. 8.8 系统的确定性辐射传输选项的实现，可以在临床可行的计算时间内，获得与蒙特卡罗模拟这一金标准相当的准确性结果。
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