基于海马保护的2种儿童中枢神经系统生殖细胞肿瘤放疗技术的剂量学研究

目的 比较容积旋转调强放射治疗（VMAT）和调强适形放射治疗（IMRT）2种技术在儿童中枢神经系统（CNS）生殖细胞肿瘤（GCT）放疗中的海马保护和剂量学差异。 方法 回顾性分析2020年6月至2021年6月在解放军联勤保障部队第九〇〇医院接受全CNS放疗的12例GCT患儿的影像学资料，其中男性患儿4例、女性患儿8例，年龄7~14岁，中位年龄11岁。对所有患儿进行靶区及周围危及器官的勾画，分别设计VMAT计划和IMRT计划，处方剂量30 Gy，每次3 Gy，共照射10次。通过剂量体积直方图获取各剂量学参数并进行配对t检验，比较靶区及周围危及器官的剂量学差异，通过比较机器跳数和治疗时长评估计划实施效率。 结果 VMAT和IMRT 2种技术均能得到较好的靶区剂量学分布。VMAT技术的靶区均匀性略优于IMRT技术，均匀性指数分别为0.11±0.02和0.14±0.01，且差异有统计学意义（t=?5.392，P<0.001）。VMAT和IMRT2种技术的左海马最大照射剂量分别为（15.99±0.70） Gy和（21.21±1.07） Gy、右海马最大照射剂量分别为（16.13±0.58） Gy和（21.35±0.69） Gy，且差异均有统计学意义（t=?17.622、?21.628，均P<0.001），VMAT技术在海马保护上达到了剂量限制要求。VMAT技术在周围危及器官保护方面较IMRT技术优势明显，除双肺外，在眼晶状体、甲状腺、肾脏保护方面VMAT技术全面优于IMRT技术，且差异均有统计学意义（t=?8.198~?2.231，均P<0.05）。VMAT技术在治疗效率方面同样优于IMRT技术，VMAT的机器跳数为1 749±95、治疗时长为（354±31） s，均仅为IMRT技术的40%左右，且差异均有统计学意义（t=?20.883、?22.790，均P<0.001）。 结论 在儿童CNS GCT放疗中，VMAT技术能够在保护海马的情况下实现更好的靶区均匀性，同时在周围危及器官保护和治疗效率上具有明显优势。

Dosimetry study of two radiotherapy techniques for child central nervous system germ cell tumor based on hippocampus protection

Objective To compare dosimetry between volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for protecting the hippocampus in the radiotherapy of children with central nervous system (CNS) germ cell tumors (GCT). Methods Retrospective analysis was conducted on the imaging data of 12 children with GCT who received craniospinal irradiation in the 900th Hospital of the Joint Logistics Support Force of PLA from June 2020 to June 2021. The participants included 4 males and 8 females aged 7 to 14 years, with a median age of 11 years. VMAT and IMRT plans were designed after completing the delineation of the target area and the corresponding organs at risk. The prescribed dose was 30 Gy with 10 fractions. Dose-volume histogram was used to obtain various dosimetry parameters. The parameters were then analyzed using paired t-test to compare dosimetry between the target area and the corresponding organs at risk and evaluate the implementation efficiency based on machine monitor unit and treatment time. Results VMAT and IMRT plans both achieve better target dose distribution. VMAT is slightly better than IMRT in terms of the uniformity of the target area. The homogeneity index values for VMAT and IMRT are 0.11±0.02 and 0.14±0.01, respectively, and the difference is statistically significant (t=?5.392, P<0.001). The maximum doses of the left hippocampus in VMAT and IMRT are (15.99±0.70) and (21.21±1.07) Gy, and those of the right hippocampus are (16.13±0.58) and (21.35±0.69) Gy, respectively; the differences are statistically significant (t=?17.622, ?21.628; both P<0.001). VMAT meets the dose limit for hippocampal protection and has obvious advantages over IMRT in protecting organs at risk. VMAT is significantly better than IMRT in protecting the eye lens, thyroid, and kidney, and the differences are statistically significant (t=?8.198 to ?2.231, all P<0.05). In terms of treatment efficiency, VMAT is also superior to IMRT. The machine monitor unit of VMAT is 1749±95 and the treatment time is (354±31) s, which are about 40% of those of IMRT, and the differences are statistically significant (t=?20.883, ?22.790; both P<0.001). Conclusion In the radiotherapy of childhood CNS GCT, VMAT can achieve better target uniformity while protecting the hippocampus and has obvious advantages in terms of protection of the corresponding organs at risk and treatment efficiency than IMRT.