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目的 :评价容积调强弧形治疗(volumetric modulated arc therapy,VMAT)应用于儿童全脑全脊髓放疗的剂量学。方法 :对10例接受全脑全脊髓放疗的儿童分别设计传统放疗计划[X射线适形放疗(conformal radiotherapy,CRT)_X计划和电子线CRT_E计划]和VMAT计划,比较这3种放疗计划的靶区覆盖度、危及器官(organ at risk,OAR)受照剂量以及出束时间的差异。结果 :采用VMAT技术时的靶区覆盖度、靶区适形指数(conformality index,CI)和剂量均匀指数(homogeneity index,HI)分别为(95.77±0.72)%、1.01±0.03和1.08±0.01,均显著优于CRT_X技术和CRT_E技术[(90.87±1.24)%、1.09±0.08和1.14±0.02,P值均<0.01;(91.06±1.53)%、0.95±0.08和1.14±0.03,P值均<0.01]。采用VMAT技术时,OAR最大受照剂量显著低于CRT_X技术,但略高于CRT_E技术;肺、肾、脾和胃的平均受照剂量显著高于CRT_X和CRT_E技术(P<0.05或P<0.01),但心和肠的平均受照剂量较低。采用VMAT技术时,靶区外整体剂量为(7.57±0.89)Gy,显著高于CRT_X和CRT_E技术(P值均<0.01),但出束时间明显延长(P值均<0.01)。结论 :在儿童全脑全脊髓放疗中,传统的X射线和电子线放疗技术的治疗效率较高,大多数OAR均能得到较好的保护;而VMAT技术的靶区覆盖度和剂量均匀性相对较好,但会明显增加低剂量区体积并延长出束时间,须谨慎考虑可能引发的不良反应及安全性问题。
OBJECTIVE: To evaluate the dose-modulated arc therapy (volumetric modulated arc therapy, VMAT) for pediatric whole-brain radiotherapy. Methods: The conventional radiotherapy programs [conformal radiotherapy (CRT) _X plan and electronic line CRT_E plan] and VMAT plan were designed for 10 children receiving whole-brain radiotherapy. The targets of the three radiotherapy plans were compared District coverage, organ at risk (OAR) exposure dose and time to beam differences. Results: The target area coverage, target conformality index (CI) and homogeneity index (HI) were (95.77 ± 0.72)%, 1.01 ± 0.03 and 1.08 ± 0.01, (P <0.01); (91.06 ± 1.53)%, 0.95 ± 0.08 and 1.14 ± 0.03, P values were significantly lower than CRT_X and CRT_E techniques [(90.87 ± 1.24)%, 1.09 ± 0.08 and 1.14 ± 0.02, 0.01]. With VMAT, the maximum dose of OAR was significantly lower than that of CRT_X, but slightly higher than that of CRT_E. The mean doses of lung, kidney, spleen and stomach were significantly higher than those of CRT_X and CRT_E (P <0.05 or P <0.01 ), But the average heart and bowel exposure dose is lower. With VMAT, the overall dose outside the target area was (7.57 ± 0.89) Gy, which was significantly higher than that of CRT_X and CRT_E techniques (all P <0.01), but the beam-out time was significantly prolonged (P <0.01). Conclusion: The traditional X-ray and electron beam radiotherapy techniques are more effective in the treatment of whole-brain whole-body radiotherapy in children, and most OARs can be well protected. However, the target coverage and dose uniformity of VMAT are relative It is better, but it will significantly increase the volume of low-dose zone and prolong the beam-out time. Careful consideration should be given to possible adverse reactions and safety issues.