基于肺部模体研究处方等剂量线对射波刀计划质量的影响

Lung phantom-based study on the effect of prescription isodose line on CyberKnife plan quality

目的:基于仿真肺部模体研究不同处方等剂量线(PIDL)的选取对射波刀计划质量的影响。方法:以仿真肺部模体中球方中心球体外扩3mm作为靶区,体积13.46cc,设置3个剂量限值壳层,分别距离靶区表面2、15和25mm。按照已制定的方案优化计划,在靶区处方覆盖率大于98%的情况下获得不同PIDL计划。结果:采用蒙特卡罗算法计算剂量获得40%~73%PIDL计划,其中剂量梯度指数、均匀性指数和V25与PIDL相关系数分别为0.960(P<0.01)、-1.000(P<0.01)和0.673(P=0.033),其它参数与PIDL的相关性无统计学意义。结论:肺部模体的射波刀计划参数中剂量梯度指数、均匀性指数和V25与PIDL显著性相关。50%左右PIDL计划具有较陡峭剂量跌落梯度,同时较高或较低PIDL计划可能导致靶区剂量适形性下降。

Objective To study the effects of prescription isodose line (PIDL) on the quality of CyberKnife plans designed on anthropomorphic lung phantom. Methods The spherical center sphere in anthropomorphic lung phantom was expanded 3 mm and selected as the target area, with a volume of 13.46 cc. Three dose-limit shells were set to be 2, 15 and 25 mm from the target surface, respectively. The plans were optimized according to predesigned strategy, and the plans of different PIDL were obtained under the condition that the prescription coverage of target area was above 98%. Results Monte Carlo algorithm for dose calculation was used to obtain the plans of 40% to 73% PIDL, in which the correlation coefficients of dose gradient index, homogeneity index and V25 with PIDL were 0.960 (P<0.01),- 1.000 (P<0.01) and 0.673 (P=0.033), respectively. There was no statistically significant correlation between other parameters and PIDL. Conclusion Among the parameters of CyberKnife plans designed on lung phantom, dose gradient index, homogeneity index and V25 were significantly correlated with PIDL. The plan of about 50% PIDL has a sharper dose falloff gradient, and the plan of higher or lower PIDL may lead to a decreased dose conformity in target areas.