Mourtada Firas, Mikell Justin, Ibbott Geoffrey
Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
Brachytherapy. 2012 May-Jun;11(3):237-44. doi: 10.1016/j.brachy.2011.06.002. Epub 2011 Aug 3.
The purpose of this study was to determine the dosimetric parameters of the AgX100, a new (125)I brachytherapy seed model, using Monte Carlo (MC) simulations according to the protocol specified by the updated American Association of Physicists in Medicine Task Group No. 43 Report (TG-43U1) and compare these parameters with those of the established brachytherapy (125)I seed models 6711 and I25.S06.
Independent verification of the new seed geometry was performed using high-resolution digital radiography and scanning electron microscopy. MCNPX v.2.5 MC simulations of the AgX100 seed were performed to derive its TG-43U1 parameters, the dose rate constant, the radial dose function, and the two- and one-dimensional anisotropy functions in liquid water. A dosimetric error propagation analysis was also performed to include uncertainty because of seed manufacturing tolerances and physics parameters.
The MC-calculated dose rate constant for the AgX100 seed was 0.943cGy·h(-1)·U(-1)±2.6% (k=1) based on the air kerma strength for a simulated point detector. Tabulated results of the radial dose function for line and point source approximations and the two-dimensional anisotropy function are also reported.
The MC-predicted dose distribution of the AgX100 seed was found to be comparable with that of the model 6711 seed but much different from the dose distribution of the model I25.S06 seeds. However, at shallow distances, there were some dosimetric differences between the AgX100 and 6711 seed, which warrant separate TG-43U1 parameters for use in clinical treatment planning systems.
本研究的目的是根据更新后的美国医学物理学家协会第43号任务组报告（TG - 43U1）规定的协议，使用蒙特卡罗（MC）模拟确定新型（125）I近距离放射治疗种子模型AgX100的剂量学参数，并将这些参数与已确立的近距离放射治疗（125）I种子模型6711和I25.S06的参数进行比较。
使用高分辨率数字射线照相和扫描电子显微镜对新种子的几何形状进行独立验证。对AgX100种子进行MCNPX v.2.5 MC模拟，以得出其TG - 43U1参数、剂量率常数、径向剂量函数以及液态水中的二维和一维各向异性函数。还进行了剂量学误差传播分析，以纳入由于种子制造公差和物理参数导致的不确定性。
基于模拟点探测器的空气比释动能强度，AgX100种子的MC计算剂量率常数为0.943cGy·h⁻¹·U⁻¹±2.6%（k = 1）。还报告了线源和点源近似的径向剂量函数以及二维各向异性函数的列表结果。
发现AgX100种子的MC预测剂量分布与6711型种子的剂量分布相当，但与I25.S06型种子的剂量分布有很大不同。然而，在浅距离处，AgX100和6711种子之间存在一些剂量学差异，这需要在临床治疗计划系统中使用单独的TG - 43U1参数。
