目的。在计算机断层扫描前(CT)时代接受治疗的儿童癌症幸存者的放射流行病学研究在计算体模上重建了患者的治疗领域。对于这样的研究,由于年龄是通常可用的人体测量参数,因此在放射治疗时通常会根据年龄对体模进行缩放。在此类研究中使用了几种参考尺寸的体模,但参考尺寸体模仅在离散年龄(例如:新生儿,1、5、10、15和成人)。当这种体模用于RT剂量重建时,选择最近的离散年龄体模来代表特定年龄的幸存者。在这项工作中,我们(1)进行了一项可行性研究,将离散年龄的参考尺寸体模放大到其他不同年龄,(2)评估了使用精确年龄缩放的体模而不是离散年龄的最接近年龄匹配的体模的剂量学影响。方法。我们采用了佛罗里达大学/国家癌症研究所(UF/NCI)计算幻影库进行研究。对于可行性研究,8个男性和女性参考尺寸UF/NCI体模(5、10、15和35岁)被缩小到14个不同的年龄,其中包括最近的可用较低的离散年龄(1、5、10和15岁)和在Wilms肿瘤RT(3.9岁)时的中位年龄,颅骨(8.0年),以及接受RT治疗的儿童癌症幸存者研究(CCSS)扩展队列中的所有幸存者(9.1岁)。缩小是使用我们的内部年龄缩放函数(ASF)进行的。要以几何方式验证缩放,骰子相似系数(DSC),平均协议距离(MDA),和欧几里得距离(ED)之间的缩放和地面真实离散年龄的体模(未缩放的UF/NCI)为全身计算,大脑,心,肝脏,胰腺,还有肾脏.此外,将缩放幻影的高度与地面实况幻影的高度进行比较,疾病控制和预防中心(CDC)报告了身高的第50百分位数。将鳞片状器官肿块与真实器官肿块进行比较。对于剂量测定评估,对于两项不同的辐射剂量研究,1个参考大小体模和17个不同体重指数(BMI)的5岁体模(9男8女)被缩减至3.9岁的维度.对于第一项研究,我们在参考尺寸5岁和3.9岁(均为健康BMI)上模拟了6MV光子右侧侧面场RT计划,在两种情况下保持字段大小相同。计算胰腺的体积接受剂量≥15Gy(V15)的百分比和平均剂量,肝脏,和胃。对于第二项研究,同样的治疗方案,但是依赖于患者解剖结构的视野大小,在17个与身体大小相关的5岁和3.9岁的体模上进行了模拟,这些体模具有不同的BMI。V15,平均剂量,和1%体积(D1)接受的最小剂量,按95%的体积(D95)计算胰腺,肝脏,胃,左肾(对侧),右肾,左右冒号,胆囊,胸椎,和腰椎。进行非参数Wilcoxon秩和检验以确定对精确年龄缩放和最接近年龄匹配体模的器官的剂量是否显著不同(p<0.05)。结果。在可行性研究中,获得的最佳DSCs为脑(中位数:0.86)和全身(中位数:0.91),而肾脏(中位数:0.58)和胰腺(中位数:0.32)的一致性较差.在MDA和ED的情况下,全身,大脑,与其他器官相比,肾脏的分布更紧密,中值更低。为了进行高度比较,总体一致性在2.8%(3.9厘米)和3.0%(3.2厘米)的地面实况UF/NCI和CDC报告的第50百分位高度内,分别。对于质量比较,缩放和地面真实器官质量之间的最大百分比和绝对差异在31.3%(29.8g)和211.8g(16.4%)内,分别(在所有年龄段)。在第一个剂量学研究中,V15和平均剂量的绝对差异高达6%和1.3Gy,分别。在第二个剂量学研究中,除完全束内器官外,所有研究器官的V15和平均剂量均显着不同(p<0.05)。D1和D95对大多数器官没有显着差异(p>0.05)。结论。我们通过将UF/NCI计算体从一个年龄扩展到另一个年龄,成功地评估了我们的ASF,这证明了缩放任何基于CT的解剖结构的可行性。我们发现,精确的按年龄缩放的体模和最近的年龄匹配体模的器官剂量存在显着差异(p<0.05),这表明使用精确的按年龄缩放的体模进行回顾性剂量学研究是一种更好的方法。
Purpose.Radiation epidemiology studies of childhood cancer survivors treated in the pre-computed tomography (CT) era reconstruct the patients\' treatment fields on computational phantoms. For such studies, the phantoms are commonly scaled to age at the time of radiotherapy treatment because age is the generally available anthropometric parameter. Several reference size phantoms are used in such studies, but reference size phantoms are only available at discrete ages (e.g.: newborn, 1, 5, 10, 15, and Adult). When such phantoms are used for RT dose reconstructions, the nearest discrete-aged phantom is selected to represent a survivor of a specific age. In this work, we (1) conducted a feasibility study to scale reference size phantoms at discrete ages to various other ages, and (2) evaluated the dosimetric impact of using exact age-scaled phantoms as opposed to nearest age-matched phantoms at discrete ages.Methods.We have adopted the University of Florida/National Cancer Institute (UF/NCI) computational phantom library for our studies. For the feasibility study, eight male and female reference size UF/NCI phantoms (5, 10, 15, and 35 years) were downscaled to fourteen different ages which included next nearest available lower discrete ages (1, 5, 10 and 15 years) and the median ages at the time of RT for Wilms\' tumor (3.9 years), craniospinal (8.0 years), and all survivors (9.1 years old) in the Childhood Cancer Survivor Study (CCSS) expansion cohort treated with RT. The downscaling was performed using our in-house age scaling functions (ASFs). To geometrically validate the scaling, Dice similarity coefficient (DSC), mean distance to agreement (MDA), and Euclidean distance (ED) were calculated between the scaled and ground-truth discrete-aged phantom (unscaled UF/NCI) for whole-body, brain, heart, liver, pancreas, and kidneys. Additionally, heights of the scaled phantoms were compared with ground-truth phantoms\' height, and the Centers for Disease Control and Prevention (CDC) reported 50th percentile height. Scaled organ masses were compared with ground-truth organ masses. For the dosimetric assessment, one reference size phantom and seventeen body-size dependent 5-year-old phantoms (9 male and 8 female) of varying body mass indices (BMI) were downscaled to 3.9-year-old dimensions for two different radiation dose studies. For the first study, we simulated a 6 MV photon right-sided flank field RT plan on a reference size 5-year-old and 3.9-year-old (both of healthy BMI), keeping the field size the same in both cases. Percent of volume receiving dose ≥15 Gy (V15) and the mean dose were calculated for the pancreas, liver, and stomach. For the second study, the same treatment plan, but with patient anatomy-dependent field sizes, was simulated on seventeen body-size dependent 5- and 3.9-year-old phantoms with varying BMIs. V15, mean dose, and minimum dose received by 1% of the volume (D1), and by 95% of the volume (D95) were calculated for pancreas, liver, stomach, left kidney (contralateral), right kidney, right and left colons, gallbladder, thoracic vertebrae, and lumbar vertebrae. A non-parametric Wilcoxon rank-sum test was performed to determine if the dose to organs of exact age-scaled and nearest age-matched phantoms were significantly different (p < 0.05).Results.In the feasibility study, the best DSCs were obtained for the brain (median: 0.86) and whole-body (median: 0.91) while kidneys (median: 0.58) and pancreas (median: 0.32) showed poorer agreement. In the case of MDA and ED, whole-body, brain, and kidneys showed tighter distribution and lower median values as compared to other organs. For height comparison, the overall agreement was within 2.8% (3.9 cm) and 3.0% (3.2 cm) of ground-truth UF/NCI and CDC reported 50th percentile heights, respectively. For mass comparison, the maximum percent and absolute differences between the scaled and ground-truth organ masses were within 31.3% (29.8 g) and 211.8 g (16.4%), respectively (across all ages). In the first dosimetric study, absolute difference up to 6% and 1.3 Gy was found for V15and mean dose, respectively. In the second dosimetric study, V15and mean dose were significantly different (p < 0.05) for all studied organs except the fully in-beam organs. D1and D95were not significantly different for most organs (p > 0.05).Conclusion.We have successfully evaluated our ASFs by scaling UF/NCI computational phantoms from one age to another age, which demonstrates the feasibility of scaling any CT-based anatomy. We have found that dose to organs of exact age-scaled and nearest aged-matched phantoms are significantly different (p < 0.05) which indicates that using the exact age-scaled phantoms for retrospective dosimetric studies is a better approach.