a Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, Maryland 20850.
d Department of Nuclear Engineering, Texas A&M University, College Station, Texas 77843.
Radiat Res. 2018 Jun;189(6):618-626. doi: 10.1667/RR14999.1. Epub 2018 Apr 4.
Epidemiological investigation is an important approach to assessing the risk of late effects after radiotherapy, and organ dosimetry is a crucial part of such analysis. Computed tomography (CT) images, if available, can be a valuable resource for individualizing the dosimetry, because they describe the specific anatomy of the patient. However, CT images acquired for radiation treatment planning purposes cover only a portion of the body near the target volume, whereas for epidemiology, the interest lies in the more distant normal tissues, which may be located outside the scan range. To address this challenge, we developed a novel method, called the Anatomically Predictive Extension (APE), to extend a partial-body CT image stack using images of a computational human phantom matched to the patient based on their height and weight. To test our method, we created five APE phantoms from chest and abdominal images extracted from the chest-abdomen-pelvis (CAP) CT scans of five patients. Organ doses were calculated for simple chest and prostate irradiations that were planned on the reference computational phantom (assumed patient geometry if no CT images are available), APE phantoms (patient-phantom hybrid given a partial-body patient CT) and full patient CAP CT scans (ground truth). The APE phantoms and patient CAP CT scans resulted in nearly identical dosimetry for those organs that were fully included in the partial-body CT used to construct the APE. The calculated doses to these same organs in the reference phantoms differed by up to 20% and 52% for the chest and prostate cases, respectively. For organs outside the scan coverage, the reference phantom showed, on average, dose differences of 31% (chest case) and 41% (prostate case). For the APE phantoms, these values were 26% (chest) and 17% (prostate). The APE method combines patient and phantom images to improve organ dosimetry both inside and outside the scan range. We intend to use the APE method for estimating dose for organs peripheral to the treatment fields; however, this method is quite generalizable with many potential applications.
流行病学调查是评估放射治疗后晚期效应风险的重要方法，而器官剂量学是这种分析的关键部分。如果有 CT 图像，它们可以成为个体化剂量学的有价值资源，因为它们描述了患者的特定解剖结构。然而，为放射治疗计划目的而采集的 CT 图像仅覆盖靶区附近身体的一部分，而对于流行病学研究，感兴趣的是更远的正常组织，这些组织可能位于扫描范围之外。为了解决这个挑战，我们开发了一种新方法，称为解剖预测扩展（APE），该方法使用基于患者身高和体重与患者匹配的计算人体模型的图像来扩展部分身体 CT 图像堆栈。为了测试我们的方法，我们从五个患者的胸部-腹部-骨盆（CAP）CT 扫描中提取了胸部和腹部图像，创建了五个 APE 幻影。为简单的胸部和前列腺照射进行了器官剂量计算，这些照射是在参考计算幻影（如果没有 CT 图像，则假设为患者几何形状）、APE 幻影（部分身体患者 CT 给出的患者-幻影混合体）和全患者 CAP CT 扫描（地面真相）上进行的。对于完全包含在用于构建 APE 的部分身体 CT 中的那些器官，APE 幻影和患者 CAP CT 扫描几乎得到了相同的剂量。对于相同的器官，参考幻影的计算剂量分别相差 20%和 52%，分别用于胸部和前列腺病例。对于扫描覆盖范围之外的器官，参考幻影平均显示出 31%（胸部病例）和 41%（前列腺病例）的剂量差异。对于 APE 幻影，这些值分别为 26%（胸部）和 17%（前列腺）。APE 方法结合了患者和幻影图像，以提高扫描范围内外的器官剂量学。我们打算使用 APE 方法来估计治疗野外周围器官的剂量；然而，这种方法具有很强的通用性，有许多潜在的应用。
