关键词: 儿童生殖细胞瘤, 全脑放射治疗, 摆位累积误差, 自适应放射治疗, 剂量偏差

Abstract: Objective  To investigate the feasibility of adaptive radio therapy (ART) based on image guided-radiotherapy (IGRT) for pediatric germ cell tumors and to provide a basis for clinical whole-brain ART. Methods  A retrospective study was performed for 20 patients with germ cell tumors (GCTs) of the central nervous system who underwent whole brain prophylactic radiotherapy. Each patient underwent cone beam computed tomography (CBCT) once a week for the first three and subsequent treatments for a total of 7 sessions. Record the positioning error values in the lateral (LAT),  longitudinal (LNG), and vertical (VRT) directions during the entire treatment process. The original plan was named Plan_A, and a new treatment center point (ISO) regression treatment plan system was generated due to the positioning error value, and the volume dose was calculated without changing the field weight and field distribution, and the Plan Sum function was used to add the cumulative positioning error to generate a new plan to obtain Plan_B. The new plan generated by the cumulative positioning error is quickly optimized by the Acuros XB algorithm and added to the Plan Sum function to obtain Plan_C. The target and organ at risk (OAR) dose changes of Plan_A, Plan_B and Plan_C were compared, and the statistical differences were verified by Wilcoxon's paired rank test. Results  Compared with Plan_A, Plan_B homogeneity index (HI) 95  planning target volume(PTV) and HI98 PTV were 1.058 4－1.084 7. Conformity index (CI) PTV was 0.934 4. CTV D_min relative deviation was -7.22%, P=0.000 7. OAR relative deviation was －0.1%－9.8%. Compared with Plan_ A, HI95 PTV and HI98 PTV of Plan_ C were 1.056 9－1.078 8. CI PTV was 0.936 5. CTV D_min relative deviation was -1.69%, P=0.545 9. OAR relative deviation was  －0.15%－3.40%. Conclusion  There were statistical differences in the cumulative positioning error of whole brain radiotherapy for childhood germ cell tumor on the dose of target area and endangered organs, and the cumulative positioning error led to the deterioration of target uniformity and conformity, the Dmin change of CTV exceeded 5%, and the OAR reception increased. ART rescheduling can bring target uniformity and conformity and the amount of hazardous organs closer to the original plan. At the same time Plan_B although there is a relative deviation, the absolute dose of the endangering organ is within a reasonable range.

Key words: pediatric germ cell tumor, whole brain radiotherapy, cumulative set-up error, adaptive radiotherapy, dose deviation