容积旋转调强与固定野动态调强低剂量区比较

Comparison of low dose area in volumetric modulated arc therapy and static intensity modulated radiotherapy

目的:对容积旋转调强(VMAT)和不同射野数的固定野动态调强(IMRT)的低剂量区进行比较,探讨具有低剂量敏感危及器官的肿瘤适用射野技术。方法:用Eclipse 10.0计划系统,在(30×30×30)cm^3均匀模体中模仿常见肿瘤,从简单到复杂依次勾画圆形、C形、H形、S形、X形及π形靶区,给予处方50 Gy/25 Fx,用5野、7野、9野IMRT和VMAT进行计划设计,所有优化限制条件均相同。将靶区外缘2.5 cm至模体表面区域作为低剂量统计区,统计不同技术低剂量区的V_5、V_(10)、V_(15)、V_(20)、V_(30)及平均剂量差异,以及靶区适形指数(CI)。结果:5野IMRT V_5、V_(10)、V_(15)低剂量区与VMAT和7,9野IMRT相比较低,有统计意义。VMAT的CI比IMRT好,VMAT的V_(30)体积与5野和7野IMRT相比更低,与9野技术没有统计学差异。其他低剂量区VMAT和IMRT相比没有统计学意义。结论:对于肿瘤周围有低剂量敏感危及器官的肿瘤,比如胸部肿瘤,V_5低剂量区会增加2级以上放射性肺炎发生率,所以尽可能采用5野以下IMRT。危及器官对低剂量区不敏感的其他部位肿瘤,VMAT技术与IMRT相比有更好的靶区适形度,治疗时间更短,所以VMAT技术有较大优势。

Objective To discuss on the appropriate treatment technology for the tumor with organs at risk sensitive to low dose volume by comparing the low dose area of volumetric modulated arc therapy（VMAT） and static intensity modulated radiotherapy（IMRT） with different field numbers. Methods Eclipse 10.0 planning system was used to simulate common tumors, and contour target volumes from simple to complex including the volumes of circular, C, H, S, X and π shapes in the homogeneous phantom of（30 × 30 × 30） cm^3. All the target volumes were given the prescription dose of 50 Gy/25 Fx.Based on the same optimizing constrains, VMAT and static IMRT respectively with 5, 7, 9 fields were used to design the treatment plan. The area between 2.5 cm outside the target volume and the surface of phantom was taken as the low dose statistical area. The differences in V_5, V_（10）, V_（15）, V_（20）, V_（25）, V_（30） and mean dose of low dose area, and conformal index（CI） were statistically analyzed. Results The V_5, V_（10）, V_（15） of 5-field static IMRT were less than those of VMAT and IMRT with 7 or 9 fields, with statistical significance; CI of VMAT was better than that of static IMRT; the V_（30） of VMAT was less than that of static IMRT with 5 or 7 fields, and the V_（30） of VMAT didn＇t show statistical differences with that of 9-field static IMRT. No significant differences were found in the other low dose areas among VMAT and IMRT with 5, 7 or 9 fields. Conclusion For the tumor surrounded by organs at risk sensitive to low dose volume, such as thoracic tumor, V_5 low dose area increases the incidence of radioactive pneumonia above level 2, so static IMRT with 5 fields or less than 5 fields is much better. For other tumors without organs at risk sensitive to low dose volume, VMAT has greater advantages, with better CI and treatment time than static IMRT.