Oregon State University, Corvallis, OR, United States of America. Oregon Health and Science University, Portland, OR, United States of America.
Phys Med Biol. 2018 Jan 11;63(2):025021. doi: 10.1088/1361-6560/aa9838.
The purpose of this study was to develop a straightforward method of supplementing patient anatomy and estimating out-of-field absorbed dose for a cohort of pediatric radiotherapy patients with limited recorded anatomy. A cohort of nine children, aged 2-14 years, who received 3D conformal radiotherapy for low-grade localized brain tumors (LBTs), were randomly selected for this study. The extent of these patients' computed tomography simulation image sets were cranial only. To approximate their missing anatomy, we supplemented the LBT patients' image sets with computed tomography images of patients in a previous study with larger extents of matched sex, height, and mass and for whom contours of organs at risk for radiogenic cancer had already been delineated. Rigid fusion was performed between the LBT patients' data and that of the supplemental computational phantoms using commercial software and in-house codes. In-field dose was calculated with a clinically commissioned treatment planning system, and out-of-field dose was estimated with a previously developed analytical model that was re-fit with parameters based on new measurements for intracranial radiotherapy. Mean doses greater than 1 Gy were found in the red bone marrow, remainder, thyroid, and skin of the patients in this study. Mean organ doses between 150 mGy and 1 Gy were observed in the breast tissue of the girls and lungs of all patients. Distant organs, i.e. prostate, bladder, uterus, and colon, received mean organ doses less than 150 mGy. The mean organ doses of the younger, smaller LBT patients (0-4 years old) were a factor of 2.4 greater than those of the older, larger patients (8-12 years old). Our findings demonstrated the feasibility of a straightforward method of applying supplemental computational phantoms and dose-calculation models to estimate absorbed dose for a set of children of various ages who received radiotherapy and for whom anatomies were largely missing in their original computed tomography simulations.
本研究旨在开发一种简单的方法，以补充患者解剖结构并估算一组接受三维适形放疗的局限性脑肿瘤（LBT）低龄儿童的场外吸收剂量。本研究随机选择了九名年龄在 2 至 14 岁之间的儿童，他们因低级别局限性脑肿瘤接受了 3D 适形放疗。这些患者的计算机断层扫描模拟图像集仅为颅部。为了近似他们缺失的解剖结构，我们使用先前研究中具有更大性别、身高和体重匹配范围的患者的计算机断层扫描图像补充了 LBT 患者的图像集，并且已经为这些患者勾画了放射性癌症风险器官的轮廓。使用商业软件和内部代码，在 LBT 患者的数据和补充计算体模之间进行了刚性融合。采用临床委托的治疗计划系统计算场内剂量，并采用先前开发的分析模型估算场外剂量，该模型是根据颅内放疗的新测量结果重新拟合的参数。在本研究中，患者的红骨髓、剩余组织、甲状腺和皮肤中发现了大于 1 Gy 的平均剂量。女孩的乳腺组织和所有患者的肺部观察到 150 mGy 至 1 Gy 之间的平均器官剂量。远处器官，即前列腺、膀胱、子宫和结肠，接受的平均器官剂量小于 150 mGy。年龄较小、体型较小的 LBT 患者（0-4 岁）的平均器官剂量比年龄较大、体型较大的患者（8-12 岁）高 2.4 倍。我们的研究结果表明，应用补充计算体模和剂量计算模型来估算一组接受放疗且其原始计算机断层扫描模拟中大部分解剖结构缺失的不同年龄段儿童的吸收剂量的简单方法是可行的。
