Radiation Physics Department, ERESA, Hospital General Universitario, E-46014 Valencia, Spain.
Med Phys. 2011 Jan;38(1):487-94. doi: 10.1118/1.3531973.
Recently, the manufacturer of the HDR 192Ir mHDR-v2 brachytherapy source reported small design changes (referred to herein as mHDR-v2r) that are within the manufacturing tolerances but may alter the existing dosimetric data for this source. This study aimed to (1) check whether these changes affect the existing dosimetric data published for this source; (2) obtain new dosimetric data in close proximity to the source, including the contributions from 192Ir electrons and considering the absence of electronic equilibrium; and (3) obtain scatter dose components for collapsed cone treatment planning system implementation.
Three different Monte Carlo (MC) radiation transport codes were used: MCNP5, PENELOPE2008, and GEANT4. The source was centrally positioned in a 40 cm radius water phantom. Absorbed dose and collision kerma were obtained using 0.1 mm (0.5 mm) thick voxels to provide high-resolution dosimetry near (far from) the source. Dose-rate distributions obtained with the three MC codes were compared.
Simulations of mHDR-v2 and mHDR-v2r designs performed with three radiation transport codes showed agreement typically within 0.2% for r > or = 0.25 cm. Dosimetric contributions from source electrons were significant for r < 0.25 cm. The dose-rate constant and radial dose function were similar to those from previous MC studies of the mHDR-v2 design. The 2D anisotropy function also coincided with that of the mHDR-v2 design for r > or = 0.25 cm. Detailed results of dose distributions and scatter components are presented for the modified source design.
Comparison of these results to prior MC studies showed agreement typically within 0.5% for r > or = 0.25 cm. If dosimetric data for r < 0.25 cm are not needed, dosimetric results from the prior MC studies will be adequate.
最近，HDR 192Ir mHDR-v2 近距离放射治疗源的制造商报告了一些小的设计变更（此处称为 mHDR-v2r），这些变更在制造公差范围内，但可能会改变该源的现有剂量学数据。本研究旨在：（1）检查这些变化是否会影响为该源发布的现有剂量学数据；（2）在靠近源的地方获得新的剂量学数据，包括 192Ir 电子的贡献，并考虑不存在电子平衡的情况；（3）获得用于塌陷锥治疗计划系统实施的散射剂量分量。
使用三种不同的蒙特卡罗（MC）辐射传输代码：MCNP5、PENELOPE2008 和 GEANT4。将源置于 40cm 半径水模体的中心位置。使用 0.1mm（0.5mm）厚的体素来获得吸收剂量和碰撞比释动能，以在靠近（远离）源的地方提供高分辨率剂量学。比较了三种 MC 代码获得的剂量率分布。
使用三种辐射传输代码对 mHDR-v2 和 mHDR-v2r 设计的模拟通常在 r≥0.25cm 时，结果差异在 0.2%以内。r＜0.25cm 时，源电子的剂量贡献显著。剂量率常数和径向剂量函数与之前对 mHDR-v2 设计的 MC 研究相似。对于 r≥0.25cm，二维各向异性函数也与 mHDR-v2 设计的结果一致。为修改后的源设计提供了剂量分布和散射分量的详细结果。
将这些结果与之前的 MC 研究进行比较，结果在 r≥0.25cm 时通常差异在 0.5%以内。如果不需要 r＜0.25cm 的剂量学数据，则先前 MC 研究的剂量学结果将是足够的。
