射波刀计划设计中治疗路径选择对靶区剂量分布的影响

【摘 要】 目的:研究射波刀治疗计划不同治疗模式选择不同准直器治疗路径对剂量分布的影响。 方法:回顾性分析10例行射波刀治疗的脑部肿瘤患者，10例患者共18个肿瘤，肿瘤体积（9.7±10.4） cc，每个肿瘤计划设计时添加两个剂量限制环，环距离靶区5及15 mm，其中相对规则的6个靶区选取等中心治疗模式，其余选择非等中心模式，观察各个肿瘤的靶区分布情况。 结果:6例规则肿瘤，适形度指数（CI），新适形度指数（NCI），包绕体积（Coverage），以及治疗节点数（Node），第一条路径（Path1, P1）与其余两条路径相比具有统计学意义。对于CI，P值分别为0.019、0.076、0.819；对于NCI，P值分别为0.031、0.733、0.014；对于Coverage，P值分别为0.009、0.960、0.032；对于Node，P值为0.000、0.584、0.000。12例非等中心治疗模式的肿瘤，选取4 cm的肿瘤进行分析，大小为20 mm的准直器得出最佳的剂量适形度及相对合适的治疗时间。 结论:规则靶区，选取等中心治疗模式，同样可以得出较好的计划质量，射波刀的治疗计划系统的3条路径在使用过程中具有明显差别。在设计时，建议优先选择P1，同时避免选择靶区附近危及器官一侧的治疗路径节点。不规则靶区，选择非等中心治疗模式，建议选择肿瘤短径的70%大小的限光筒，使肿瘤的治疗时间及治疗适形度等得到最优化的计算。

Effects of treatment paths on target dosimetric distribution in CyberKnife radiotherapy plan

Abstract: Objective To analyze the effects of different treatment paths on the dosimetric distribution in CyberKinfe radiotherapy plan. Methods The clinical data of 10 patients receiving CyberKinfe treatment for brain tumors were retrospectively analyzed in this study. A total of 18 tumors were found in 10 patients, with a mean volume of (9.7±10.4) cc. Two dose-limit rings were created at the distance of 5 and 15 mm to target areas. Isocenter treatment model was adopted for 6 regular tumors, and non-isocenter treatment model was adopted for the rest. The target dosimetric distributions were analyzed. Results For 6 regular tumors, the conformity index, the new conformity index, coverage, and number of nodes of the first treatment path (P1) were significant different from those of the other two treatment paths. P value was 0.019, 0.076, 0.819 for conformity index, 0.031, 0.733, 0.014 for the new conformity index, 0.009, 0.960, 0.032 for coverage, and 0.000, 0.584, 0.000 for the number of nodes. Among the 12 tumors treated by non-isocenter treatment, only the tumor with a diameter of 4 cm were analyzed and the result showed that using 20 mm collimator achieved the best conformity index and acceptable treatment time. Conclusion Isocenter treatment for regular tumors achieves better conformity index. The 3 treatment paths on CyberKinfe treatment planning system have obvious differences in treatment planning. The first treatment path should be the first choice during the treatment planning, and the treatment paths on the side of organs-at-risk should be avoided. Non-isocenter treatment is adopted for irregular tumors, and selecting collimator which is 70% of the short diameter of the tumor will achieve an optimal treatment time and the best conformity index.