Patel Samir, Drodge Suzanne, Jacques Amanda, Warkentin Heather, Powell Kent, Chafe Susan
Department of Radiation Oncology, Cross Cancer Institute, Edmonton, Canada.
Department of Radiation Oncology, Cross Cancer Institute, Edmonton, Canada.
J Med Imaging Radiat Sci. 2015 Jun;46(2):134-140. doi: 10.1016/j.jmir.2014.11.003. Epub 2015 Jan 30.
The purpose of this study was to compare volumetric modulated arc therapy (VMAT) with helical tomotherapy (HT) and three-dimensional conformal radiation therapy (3D-CRT) for craniospinal irradiation (CSI) in children with medulloblastoma.
Five children treated with 3D-CRT were retrospectively replanned with HT and VMAT. Tomotherapy plans used a single helical arc, thereby eliminating field junctions. VMAT plans used two arcs rotating alternatively clockwise and counterclockwise, respectively. Conformity and homogeneity indices, dose-volume histograms, integral doses, monitor units delivered, and beam-on times were compared.
VMAT showed an improved mean conformity index of 1.05 in comparison with 3D-CRT (1.58, P = .04) and HT (1.34, P = .04). The mean homogeneity index of VMAT (1.13) was not significantly different from 3D-CRT (1.16) but higher than HT (1.08, P = .04). For normal tissues, VMAT resulted in a lower mean dose to the skin, eyes, lenses, optic nerves, cochlea, esophagus, heart, peritoneal cavity, bladder, and rectum compared with 3D-CRT (all P = .04). There were few significant differences in dose-volume statistics for normal tissues between VMAT and HT. The mean nontarget tissue integral dose for VMAT of 80.8 J was significantly lower than for 3D-CRT (91.5 J, P = .04) and HT (95.6 J, P = .04). Body and nontarget tissue integral doses were lowest with VMAT in every patient.
For CSI, VMAT provides comparable normal tissue sparing with tomotherapy and may reduce the integral dose. Compared with 3D-CRT, VMAT improved normal tissue sparing at higher doses despite larger volumes receiving lower doses. These findings have potential implications in the risk of the development of late adverse effects and radiation-related second malignancies in children with curable primary disease.
本研究旨在比较容积调强弧形放疗（VMAT）、螺旋断层放疗（HT）和三维适形放疗（3D-CRT）在髓母细胞瘤患儿全脑全脊髓照射（CSI）中的应用。
对5例接受3D-CRT治疗的患儿进行回顾性研究，重新制定HT和VMAT计划。断层放疗计划采用单螺旋弧，从而消除野间衔接。VMAT计划采用两个分别顺时针和逆时针交替旋转的弧。比较适形度和均匀性指数、剂量体积直方图、积分剂量、输出的监测单位和照射时间。
与3D-CRT（1.58，P = 0.04）和HT（1.34，P = 0.04）相比，VMAT的平均适形度指数提高到1.05。VMAT的平均均匀性指数（1.13）与3D-CRT（1.16）无显著差异，但高于HT（1.08，P = 0.04）。对于正常组织，与3D-CRT相比，VMAT使皮肤、眼睛、晶状体、视神经、耳蜗、食管、心脏、腹腔、膀胱和直肠的平均剂量更低（所有P = 0.04）。VMAT和HT在正常组织的剂量体积统计方面几乎没有显著差异。VMAT的平均非靶组织积分剂量为80.8 J，显著低于3D-CRT（91.5 J，P = 0.04）和HT（95.6 J，P = 0.04）。在每位患者中，VMAT的身体和非靶组织积分剂量最低。
对于CSI，VMAT在保护正常组织方面与断层放疗相当，并且可能降低积分剂量。与3D-CRT相比，尽管接受较低剂量的体积较大，但VMAT在较高剂量下改善了正常组织的保护。这些发现对于可治愈的原发性疾病患儿发生晚期不良反应和辐射相关第二原发性恶性肿瘤的风险具有潜在意义。
