Taddei Phillip J, Mirkovic Dragan, Fontenot Jonas D, Giebeler Annelise, Zheng Yuanshui, Kornguth David, Mohan Radhe, Newhauser Wayne D
The University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Unit 94, Houston, TX 77030, USA.
Phys Med Biol. 2009 Apr 21;54(8):2259-75. doi: 10.1088/0031-9155/54/8/001. Epub 2009 Mar 20.
Proton beam radiotherapy unavoidably exposes healthy tissue to stray radiation emanating from the treatment unit and secondary radiation produced within the patient. These exposures provide no known benefit and may increase a patient's risk of developing a radiogenic cancer. The aims of this study were to calculate doses to major organs and tissues and to estimate second cancer risk from stray radiation following craniospinal irradiation (CSI) with proton therapy. This was accomplished using detailed Monte Carlo simulations of a passive-scattering proton treatment unit and a voxelized phantom to represent the patient. Equivalent doses, effective dose and corresponding risk for developing a fatal second cancer were calculated for a 10-year-old boy who received proton therapy. The proton treatment comprised CSI at 30.6 Gy plus a boost of 23.4 Gy to the clinical target volume. The predicted effective dose from stray radiation was 418 mSv, of which 344 mSv was from neutrons originating outside the patient; the remaining 74 mSv was caused by neutrons originating within the patient. This effective dose corresponds to an attributable lifetime risk of a fatal second cancer of 3.4%. The equivalent doses that predominated the effective dose from stray radiation were in the lungs, stomach and colon. These results establish a baseline estimate of the stray radiation dose and corresponding risk for a pediatric patient undergoing proton CSI and support the suitability of passively-scattered proton beams for the treatment of central nervous system tumors in pediatric patients.
质子束放射治疗不可避免地会使健康组织暴露于治疗设备发出的杂散辐射以及患者体内产生的二次辐射中。这些辐射没有已知的益处，反而可能增加患者患放射性癌症的风险。本研究的目的是计算主要器官和组织所接受的剂量，并估计质子治疗颅脊髓照射（CSI）后杂散辐射导致的二次癌症风险。这是通过对被动散射质子治疗设备和体素化人体模型进行详细的蒙特卡罗模拟来实现的，以模拟患者情况。计算了一名接受质子治疗的10岁男孩的等效剂量、有效剂量以及发生致命二次癌症的相应风险。质子治疗包括30.6 Gy的CSI以及对临床靶区追加23.4 Gy的剂量。杂散辐射预测的有效剂量为418 mSv，其中344 mSv来自患者体外产生的中子；其余74 mSv由患者体内产生的中子引起。该有效剂量对应的致命二次癌症终生归因风险为3.4%。构成杂散辐射有效剂量主要部分的等效剂量存在于肺、胃和结肠中。这些结果为接受质子CSI治疗的儿科患者建立了杂散辐射剂量及相应风险的基线估计，并支持被动散射质子束适用于治疗儿科患者中枢神经系统肿瘤。
