HT及IMRT在儿童全中枢放疗剂量学比较及二次致癌风险评估

目的 探讨HT及IMRT计划在儿童全中枢放疗中的剂量学特点,并根据EAR模型估算儿童全中枢放疗后二次致癌风险。方法 选取2012-2017年间接受全脑全脊髓照射患者CT图像15例,勾画靶区及OAR后分别完成IMRT及HT计划,t检验两种计划间靶区HI、CI和OAR的Dmax、Dmean及V10、V20并优化临床治疗方案。根据各器官DVH及EAR模型估算比较两种计划二次致癌风险。结果 两组计划在靶区覆盖度上均能达到临床要求(100%剂量≥95%靶体积),其中HT组HI优于IMRT组(P=0.000);CI上HT组并未显示优势。但HT组对于海马保护具有绝对优势,D2%和Dmean均明显低于IMRT组(P=0.000)。对OAR保护,HT在甲状腺的Dmax、Dmean、V20及心脏的Dmax、V10均小于IMRT (P=0.001、0.002、0.014及P=0.001、0.003)。在二次致癌方面,HT组相较于IMRT组对于甲状腺和肺脏的二次致癌风险更高,甲状腺和肺脏EAR分别为28.666∶26.926(P=0.010)和20.496∶18.922(P=0.003);对胃二次致癌风险似乎较高(P=0.248),对肝脏二次致癌风险相对较小(P=0.020)。结论 在儿童保护海马的全中枢放疗中HT计划优于IMRT计划。但HT对甲状腺和肺脏有较高二次致癌风险,在计划制定时应评估这些致癌风险及其他正常组织效应的平衡。

Dosimetric comparison and assessment of second cancer risk between helical tomotherapy and intensity-modulated radiotherapy in children with craniospinal irradiation

Objective To investigate the dosimetric characteristics between helical tomotherapy (HT) and intensity-modulated radiotherapy (IMRT) plans in children receiving craniospinal irradiation and estimate the risk of radiogenic second cancer according to the excess absolute risk (EAR) model. Methods Computer-tomography scans of 15 children who received craniospinal irradiation between 2012 and 2017 were selected. HT and IMRT plans were designed for each patient after contouring the volumes of tumors and organ at risks (OARs) and then the homogeneous index (HI), conformity index (CI), the maximum dose and the mean dose of OAR, V10 and V20 were analyzed to optimize the clinical treatment plan. The second cancer risk was estimated by DVH of each organ and EAR model and statistically compared between HT and IMRT. Results Both two plans met the clinical requirements in target coverage (100% dose≥95% target volume).The HI in the HT group was significantly superior to that in the IMRT group (P=0.000) whereas no significant difference was noted in CI between two groups. Compared with the IMRT plan, HT plan possessed absolute advantage in protecting hippocampus and the D2% and Dmean were significantly lower (P=0.000).As for the protection of OAR, the Dmax, Dmean and V20 of thyroid (P=0.001,0.002 and 0.014) and Dmax,V10 of heart (P=0.001 and 0.003) in the HT plan were significantly lower than those in the IMRT plan. In terms of second cancer risk, HT plan yielded a significantly higher second cancer risk for thyroid and lung compared with IMRT the EAR in thyroid was 28.666 vs. 26.926(P=0.010) and 20.496 vs. 18.922(P=0.003) in lung. Both plans yielded a relatively high second cancer risk for stomach (P=0.248), whereas a low second cancer risk for liver (P=0.020). Conclusions HT plan is superior to IMRT plan in the hippocampus-sparing craniospinal irradiation in children. However, HT plan yields a high second cancer risk for thyroid and lung. Consequently, the balance between the carcinogenic risk and the effect on other normal tissues should be assessed in the establishment of therapeutic plan.