基于非小细胞肺癌碳离子点扫描治疗的不同优化策略研究

摘要

目的 通过设计4种碳离子点扫描优化策略,对非小细胞肺癌(NSCLC)的靶区剂量覆盖和危及器官(OARs)受量变化来评估各策略.方法 10例NSCLC粒子治疗患者,于治疗期间采集多组四维CT(4DCT)用于剂量评估.4种优化策略为单纯调强优化(IMCT-NoAS)、调强优化结合肿瘤内靶区(IGTV)组织密度设定(IMCT-ASM)、单纯单射野优化(SBO-NoAS)、单射野优化结合靶区组织密度设定(SBO-ASM).初始计划在复查4DCT数据上重新计算后与初始计划做剂量比较.结果 初始计划在复查CT数据上重新计算后各策略间靶区覆盖相近,仅IMCT-NoAS有较大剂量分布差异.而OARs剂量相对于初始计划患侧肺V20生物有效剂量(RBE)最大增加约2.0 Gy;IGTV组织密度设定计划,心脏V30最大增加RBE约1.0 Gy,而IGTV未设定的计划则最大降低RBE约0.2 Gy;脊髓的RBE最大值约有2.5 Gy差异.结论 碳离子治疗对射束路径上的肿瘤内运动变化敏感.当肿瘤在头脚方向的运动幅度>8 mm时,SBO-ASM策略有较好的靶区覆盖,但潜在导致剂量分布过冲到比初始计划剂量分布更深的位置.%Objective To evaluate the dose variation of target coverage and organs at risk ( OARs) among four planning strategies using spot-scanning carbon-ion radiotherapy for non-small cell lung cancer ( NSCLC) . Methods Ten NSCLC patients utilizing gating motion control were selected to receive dose calculation over multiple acquired 4DCT images. Four optimizing strategies consisted of intensity-modulated carbon-ion therapy ( IMCT-NoAS ) , IMCT combined with internal gross tumor volume ( IGTV ) assigned muscle ( IMCT-ASM ) , single beam optimization ( SBO ) ( SBO-NoAS ) and SBO combined with IGTV assigned muscle (SBO-ASM).The initial plan was re-calculated after the 4DCT data were reviewed and then compared with the initial plan in the dosimetry. Results For re-calculation plans with two reviewing CTs,all four strategies yielded similar planning target volume ( PTV ) coverage. Merely IMCT-NoAS strategy presented with relatively significant variations in dose distribution. Dose variation for OARs between initial and re-calculated plans:for all four strategies,V20 of ipsilateral lung was increased by approximately 2. 0 Gy (relative biological effective dose,RBE),V30 of heart was increased by approximately 1. 0 Gy (RBE) for both IGTV assigned muscle strategies,whereas decreased by approximately 0. 2 Gy ( RBE) for both IGTV non-assigned muscle strategies. The maximum dose of spinal cord was changed by 2. 5 Gy ( RBE ) . Conclusions Carbon-ion radiotherapy is sensitive to the anatomic motion within the tumors along the beam path. When the tumor motion along the head-foot (H-F) direction exceeds 8 mm,SBO-ASM strategy provides better dose coverage of target. Strategies with IGTV assignment may result in dose overshoot to a position deeper than the initial planning dose distribution.