计划靶体积概念是否适合肺癌质子调强治疗计划

Planning target volume-Is it still suitable for intensity modulated proton therapy for lung cancer?

目的基于计划靶体积(PTV)和内靶体积(ITV)概念计划差异,论述PTV概念不适合于肺癌质子调强治疗(IMPT)计划,为临床提供参考。方法基于上海质子治疗示范装置固定束模型和商业化治疗计划系统软件,对6例肺癌患者在平均CT图像上分别制作基于PTV的常规IMPT计划(PTV-IMPT)和基于ITV稳健的IMPT计划(ITV-IMPT)。所有计划均设置3个射束,采用蒙特卡罗剂量算法进行最终剂量计算。评估PTV-IMPT和ITV-IMPT计划的计划质量和稳健性能。结果ITV-IMPT、PTV-IMPT计划的ITV适形指数分别为0.58、0.43,均匀指数分别为0.96、0.92,双肺V5Gy(RBE)分别为13.1%、13.5%,脊髓Dmax分别为8.9、9.5 Gy(RBE),机器跳数分别为338、401 MU。在分别轻度扰动和重度扰动场景的7种状态下,ITV-IMPT、PTV-IMPT计划的靶区覆盖稳健性指数λ范围分别为0.003~0.032、0.02~0.28,双肺500 Gy(RBE)剂量体积指标ΔV5Gy范围分别为0.06~0.11、0.07~0.13。结论与PTV-IMPT比较,ITV-IMPT具有计划质量高、稳健性好的优势,具有重要的临床价值。因此,临床推荐使用ITV概念设计肺癌的质子调强计划。

Objective To demonstrate the concept of planning target volume(PTV)is not suitable for intensity proton therapy(IMPT)in lung cancer,plan differences were compared based on the concept of PTV and Internal target volume(ITV),aiming to provide clinical reference.Methods Six patients were retrospectively selected and approved by the local ethics committee.Each of the six patients received two IMPT plans based on a synchronous accelerator model,developed by SINAP team(Shanghai Institute of Applied Physics,China Academy Science University)and commercial treatment system:one with the PTV-based robust IMPT(PTV-IMPT)plan and the other with ITV-based robust IMPT(ITV-IMPT)plan.Three beams were set in all plans,and the final dose was calculated using Monte Carlo dose algorithm.The plan quality androbustnessof PTV-IMPT and ITV-IMPT plans were evaluatedquantitatively.Results Compared to the PTV-IMPT plan,ITV-IMPT plan showed better target conformity index(conformability index:0.58 vs.0.43),better homogeneity index(homogeneity index:0.96 vs.0.92),lower V5Gy innormal lung tissue(13.1%vs.13.5%)and maximum dose in spinal cord(8.9 Gy vs.9.5 Gy)as well as plan monitor unit(MU:338 vs.401).In addition,ITV-IMPT plan showed more robust in target coverage(0.003-0.032 vs.0.02-0.28),andnormal lung tissue was also found a bit robust in the ITV-IMPT plan(0.06-0.11,0.07-0.13).Conclusions Compared with the PTV-IMPT plan,ITV-IMPT plan has the advantages of high planning quality,well robustness and better tumor motion mitigation.Therefore,ITV concept is recommended to be applied in the IMPT plan for lung cancer.