局限期SCLC化放疗后达CR者P CI的IMRT与VMAT海马区保护剂量学研究

A dosimetric study of hippocampal-avoidance prophylactic cranial irradiation in intensity-modulated radiotherapy and volumetric modulated arc therapy for patients with localized small cell lung cancer achieving complete response after chemoradiotherapy

目的：探讨固定野IMRT和VMAT技术海马区保护脑预防照射剂量学分布特征以及海马保护的可行性及风险。方法2014年1—8月我院收治的16例局限期SCLC化放疗后达CR者行PCI，放疗处方剂量为25 Gy分10次。将CT定位图像与脑MR图像进行融合，在融合图像上勾画海马区，并外扩5 mm边界形成减量区。分别设计海马保护IMRT 、VMAT计划，评价两组计划全脑、海马区及海马外扩5 mm的剂量分布。成组t检验组间差异。结果16例患者海马区平均体积2．76 cm3（2．56～3．01） cm3。 IMRT、VMAT海马区Dmean分别为（9．04±0．20）、（10．32±0．28） Gy，较处方剂量分别减少了66．0％、61．2％（ P＝0．55）；海马减量区Dmean分别为（13．57±0．90）、（14．86±0．60） Gy，较处方剂量平均分别降低了49．0％、44．1％（ P＝0．88）。结论 IMRT及VMAT技术海马保护脑预防照射均可满足临床要求，在保证全脑治疗剂量同时降低了海马区受量，应用于脑预防照射中是可行的，为患者神经认知功能保护提供了技术保障。

Objective To investigate the dosimetric characteristics of hippocampal？avoidance prophylactic cranial irradiation （ HA？PCI ） in fixed？field intensity？modulated radiotherapy （ IMRT ） and volumetric modulated arc therapy （ VMAT） and the feasibility and risks of hippocampal avoidance. Methods Prophylactic cranial irradiation （PCI） was performed for 16 patients with localized small cell lung cancer （ SCLC） who were treated in our hospital from January to August, 2014, and achieved complete response （ CR） after chemoradiotherapy, with a prescribed dose of 25 Gy in 10 fractions. CT localization image was fused with brain MRI image to contour the hippocampus on the fused image, and the boundary of the hippocampus was extended 5 mm outward to form the area for reduced dose. IMRT and VMAT plans with hippocampal avoidance were developed separately, and the dose distribution in the whole brain, the hippocampus, and the 5？mm area outside the hippocampus was evaluated for these two plans. Independent？samples t test was applied to evaluate the difference between the two groups. Results The mean hippocampal volume in the 16 patients was 2. 76 cm3 （ range 2. 56 ？3. 01 cm3 ） . The mean radiation dose （ Dmean ） in the hippocampus during IMRT and VMAT was 9. 04± 0. 20 Gy and 10. 32± 0. 28 Gy, respectively, reduced by 66. 0% and 61. 2%, respectively, compared with the prescribed dose （ P=0. 55）;Dmean in the area for reduced dose during IMRT and VMAT was 13. 57± 0. 90 Gy and 14. 86± 0. 60 Gy, respectively, reduced by 49. 0% and 44. 1%, respectively, compared with the prescribed dose （P=0. 88）. Conclusions HA？PCI in IMRT and VMAT meets the clinical requirements, and can reduce the dose in the hippocampus while ensuring the whole？brain radiation dose, and therefore can be applied in PCI and provide a technical support to protect the patient’ s neurocognitive function.