Al-Wassia Rolina K, Ghassal Noor M, Naga Adly, Awad Nesreen A, Bahadur Yasir A, Constantinescu Camelia
*Radiation Oncology Department, King Abdulaziz University †King Faisal Specialist Hospital & Research Center, Jeddah, Saudi Arabia ‡National Cancer Institute, Cairo University, Cairo, Egypt.
J Pediatr Hematol Oncol. 2015 Oct;37(7):e405-11. doi: 10.1097/MPH.0000000000000418.
Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) provide highly conformal target radiation doses, but also expose large volumes of healthy tissue to low-dose radiation. With improving survival, more children with medulloblastoma (MB) are at risk of late adverse effects of radiotherapy, including secondary cancers. We evaluated the characteristics of IMRT and VMAT craniospinal irradiation treatment plans in children with standard-risk MB to compare radiation dose delivery to target organs and organs at risk (OAR).
Each of 10 children with standard-risk MB underwent both IMRT and VMAT treatment planning. Dose calculations used inverse planning optimization with a craniospinal dose of 23.4 Gy followed by a posterior fossa boost to 55.8 Gy. Clinical and planning target volumes were demarcated on axial computed tomography images. Dose distributions to target organs and OAR for each planning technique were measured and compared with published dose-volume toxicity data for pediatric patients.
All patients completed treatment planning for both techniques. Analyses and comparisons of dose distributions and dose-volume histograms for the planned target volumes, and dose delivery to the OAR for each technique demonstrated the following: (1) VMAT had a modest, but significantly better, planning target volume-dose coverage and homogeneity compared with IMRT; (2) there were different OAR dose-sparing profiles for IMRT versus VMAT; and (3) neither IMRT nor VMAT demonstrated dose reductions to the published pediatric dose limits for the eyes, the lens, the cochlea, the pituitary, and the brain.
The use of both IMRT and VMAT provides good target tissue coverage and sparing of the adjacent tissue for MB. Both techniques resulted in OAR dose delivery within published pediatric dose guidelines, except those mentioned above. Pediatric patients with standard-risk MB remain at risk for late endocrinologic, sensory (auditory and visual), and brain functional impairments.
调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）能提供高度适形的靶区辐射剂量，但也会使大量健康组织暴露于低剂量辐射中。随着生存率的提高，更多髓母细胞瘤（MB）患儿面临放疗晚期不良反应的风险，包括继发性癌症。我们评估了标准风险MB患儿的IMRT和VMAT全脑全脊髓照射治疗计划的特征，以比较靶器官和危及器官（OAR）的辐射剂量传递情况。
10名标准风险MB患儿均接受了IMRT和VMAT治疗计划。剂量计算采用逆向计划优化，全脑全脊髓剂量为23.4 Gy，随后后颅窝加量至55.8 Gy。在轴向计算机断层扫描图像上划定临床靶区和计划靶区体积。测量每种计划技术对靶器官和OAR的剂量分布，并与已发表的儿科患者剂量 - 体积毒性数据进行比较。
所有患者均完成了两种技术的治疗计划。对计划靶区的剂量分布和剂量 - 体积直方图以及每种技术对OAR的剂量传递进行分析和比较，结果如下：（1）与IMRT相比，VMAT的计划靶区剂量覆盖和均匀性适度但明显更好；（2）IMRT和VMAT的OAR剂量 sparing 曲线不同；（3）IMRT和VMAT均未将眼睛、晶状体、耳蜗、垂体和大脑的剂量降低至已发表的儿科剂量限值。
IMRT和VMAT的使用为MB提供了良好的靶组织覆盖和相邻组织 sparing。除上述情况外，两种技术导致的OAR剂量传递均在已发表的儿科剂量指南范围内。标准风险MB的儿科患者仍面临晚期内分泌、感觉（听觉和视觉）和脑功能损害的风险。
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