Department of Diagnostic and Therapeutic Radiology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand.
J Radiat Res. 2021 Jul 10;62(4):707-717. doi: 10.1093/jrr/rrab038.
Modern radiotherapy (RT) uses altered fractionation, long beam-on time and image-guided procedure. This study aimed to compare secondary cancer risk (SCR) associated with primary field, scatter/leakage radiations and image-guided procedure in prostate treatment using intensity-modulated RT (IMRT), CyberKnife stereotactic body RT (CK-SBRT) in relative to 3-dimensional conformal RT (3D-CRT). Prostate plans were generated for 3D-CRT, IMRT (39 fractions of 2 Gy), and CK-SBRT (five fractions of 7.25 Gy). Excess absolute risk (EAR) was calculated for organs in the primary field using Schneider's mechanistic model and concept of organ equivalent dose (OED) to account for dose inhomogeneity. Doses from image-guided procedure and scatter/leakage radiations were determined by phantom measurements. The results showed that hypofractionation relative to conventional fractionation yielded lower SCR for organs in primary field (p ≤ 0.0001). SCR was further modulated by dose-volume distribution. For organs near the field edge, like the rectum and pelvic bone, CK-SBRT plan rendered better risk profiles than IMRT and 3D-CRT because of the absence of volume peak in high dose region (relative risk [RR]: 0.65, 0.22, respectively, p ≤ 0.0004). CK-SBRT and IMRT generated more scatter/leakage and imaging doses than 3D-CRT (p ≤ 0.0002). But primary field was the major contributor to SCR. EAR estimates (risk contributions, primary field: scatter/leakage radiations: imaging procedure) were 7.1 excess cases per 104 person-year (PY; 3.64:2.25:1) for CK-SBRT, 9.93 (7.32:2.33:1) for IMRT and 8.24 (15.99:2.35:1) for 3D-CRT (p ≤ 0.0002). We conclude that modern RT added more but small SCR from scatter/leakage and imaging doses. The primary field is a major contributor of risk which can be mitigated by the use of hypofractionation.
现代放射治疗（RT）采用改变分割、长照射时间和图像引导程序。本研究旨在比较前列腺治疗中使用调强放射治疗（IMRT）、CyberKnife 立体定向体部放射治疗（CK-SBRT）与三维适形放射治疗（3D-CRT）时，原发野、散射/漏射线和图像引导程序相关的继发癌症风险（SCR）。为 3D-CRT、IMRT（39 个 2Gy 分次）和 CK-SBRT（5 个 7.25Gy 分次）生成前列腺计划。使用 Schneider 的机械模型和器官当量剂量（OED）的概念计算原发野器官的超额绝对风险（EAR），以考虑剂量不均匀性。通过体模测量确定图像引导程序和散射/漏射线的剂量。结果表明，与常规分割相比，低分割会降低原发野器官的 SCR（p≤0.0001）。SCR 还受到剂量-体积分布的调节。对于场边缘附近的器官，如直肠和骨盆骨，CK-SBRT 计划由于高剂量区域无体积峰值，因此比 IMRT 和 3D-CRT 具有更好的风险特征（相对风险 [RR]：0.65、0.22，分别为 p≤0.0004）。CK-SBRT 和 IMRT 产生的散射/漏射线和成像剂量比 3D-CRT 多（p≤0.0002）。但原发野是 SCR 的主要贡献者。EAR 估计（风险贡献，原发野：散射/漏射线：成像程序）分别为 CK-SBRT 每 104 人年 7.1 例（3.64:2.25:1）、IMRT 每 104 人年 9.93 例（7.32:2.33:1）和 3D-CRT 每 104 人年 8.24 例（15.99:2.35:1）（p≤0.0002）。我们得出结论，现代 RT 增加了散射/漏射线和成像剂量的但较小的 SCR。原发野是风险的主要贡献者，可以通过采用低分割来减轻。
