Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.
J Radiat Res. 2012 Sep;53(5):777-84. doi: 10.1093/jrr/rrs026. Epub 2012 Jul 13.
Heterogeneity correction algorithms can have a large impact on the dose distributions of stereotactic body radiation therapy (SBRT) for lung tumors. Treatment plans of 20 patients who underwent SBRT for lung tumors with the prescribed dose of 48 Gy in four fractions at the isocenter were reviewed retrospectively and recalculated with different heterogeneity correction algorithms: the pencil beam convolution algorithm with a Batho power-law correction (BPL) in Eclipse, the radiological path length algorithm (RPL), and the X-ray Voxel Monte Carlo algorithm (XVMC) in iPlan. The doses at the periphery (minimum dose and D95) of the planning target volume (PTV) were compared using the same monitor units among the three heterogeneity correction algorithms, and the monitor units were compared between two methods of dose prescription, that is, an isocenter dose prescription (IC prescription) and dose-volume based prescription (D95 prescription). Mean values of the dose at the periphery of the PTV were significantly lower with XVMC than with BPL using the same monitor units (P < 0.001). In addition, under IC prescription using BPL, RPL and XVMC, the ratios of mean values of monitor units were 1, 0.959 and 0.986, respectively. Under D95 prescription, they were 1, 0.937 and 1.088, respectively. These observations indicated that the application of XVMC under D95 prescription results in an increase in the actually delivered dose by 8.8% on average compared with the application of BPL. The appropriateness of switching heterogeneity correction algorithms and dose prescription methods should be carefully validated from a clinical viewpoint.
体部立体定向放射治疗（SBRT）中，不均匀性校正算法会对肺肿瘤剂量分布产生较大影响。回顾性分析了 20 例接受 SBRT 治疗的肺肿瘤患者的治疗计划，处方剂量为 48 Gy，分 4 次给予，在等中心处给予。这些患者分别使用不同的不均匀性校正算法进行重新计算：Eclipse 中的笔形束卷积算法与 Batho 幂律校正（BPL）、放射路径长度算法（RPL）和 iPlan 中的 X 射线体素蒙特卡罗算法（XVMC）。使用相同的机器跳数（MU）比较了三种不均匀性校正算法下计划靶区（PTV）周边（最小剂量和 D95）的剂量，比较了两种剂量处方方法（即等中心剂量处方（IC 处方）和剂量-体积处方（D95 处方）之间的 MU。使用相同的 MU，与 BPL 相比，XVMC 计算得到的 PTV 周边剂量的平均值明显较低（P < 0.001）。此外，在使用 BPL、RPL 和 XVMC 的 IC 处方下，MU 平均值的比值分别为 1、0.959 和 0.986。在 D95 处方下，它们分别为 1、0.937 和 1.088。这些观察结果表明，与 BPL 相比，D95 处方下应用 XVMC 会使实际传递剂量平均增加 8.8%。从临床角度来看，应仔细验证切换不均匀性校正算法和剂量处方方法的合理性。
