| Objective : To investigate the dosimetric characteristics of helical tomotherapy(TOMO)and intensity-modulated radiotherapy(IMRT)plans in pediatric patients received craniospinal irradiation(CSI),and estimate the risk ofradiogenic second canceraccording to the excess absolute risk(EAR)model.Methods : Computer-tomography scans of 15 pediatric patients who received CSI treatment in 2012-2017 were selected.TOMO and IMRT plans were designed for each patient after contouring the volumes of tumors and organ at risks(OARs),then the homogeneous index(HI),conformity index(CI),the maximum dose and the mean dose of OAR,dose-volume histogram were analyzedto optimize the clinical treatment plan.Differential dose volume histograms(dDVHs)were created and EARs were calculated for each organ.Results:The two plans allmeet the clinical requirements in target coverage(100% doses ? 95% volumes).HI in TOMO plan was superior to IMRT plan(P< 0.001)whereas CI in TOMO plan did not show an advantage.But TOMO planhad absolute advantage in protecting hippocampus,and its D2% and Dmean were significantly lower than those of IMRT plan(D2% 15.66±0.50/23.05±0.46,P<0.001;Dmean 9.79±0.14/20.29±0.41,P<0.001).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 TOMO plan were lower than those of IMRT plan.In the risk of radiogenic second cancer,TOMO plan had a much higher risk than IMRT for thyroid and lungs,the EAR in thyroid was28.666/26.926,P = 0.010,that in lung was 20.496/18.922,P = 0.003.Both plans had a higher risk to stomach,but there was little difference between them.The two plans were less carcinogenic risk for liver(EAR 4.2/4.0,P = 0.020).Conclusion:TOMO plan has obvious advantages in the protection of the hippocampus for children with the CSI treatment.TOMO increased the risk of radiogenic second cancer in OARs,so it is imperative to take the risk factor into consideration in the formulation of treatment protocols. |
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