Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin; Department of Radiation Oncology, University of Arizona College of Medicine, Tucson, Arizona.
Pract Radiat Oncol. 2019 Nov;9(6):e549-e558. doi: 10.1016/j.prro.2019.05.014. Epub 2019 Jun 6.
Stereotactic body radiation therapy (SBRT) is an effective therapy for treating liver malignancies. However, little is known about interfractional dose variations to adjacent organs at risk (OARs). We examine the effects of interfractional organ movement and setup variation on dose delivered to OARs in patients receiving liver SBRT.
Thirty patients treated with liver SBRT were analyzed. Daily image guidance with diagnostic quality computed tomography-on-rails imaging was performed before each fraction. In phase 1, these daily images were used to delineate all OARs including the liver, heart, right kidney, esophagus, stomach, duodenum, and large bowel in 10 patients. In phase 2, only OARS in close proximity to the target were contoured in 20 additional patients. Dose distribution on each daily computed tomography was generated, and daily doses to each OAR were recorded and compared with clinical thresholds to determine whether a daily dose excess (DDE) occurred.
In phase 1, significant interfractional dose differences between planned and delivered dose to OARs were observed, but differences were rarely clinically significant, with just 1 DDE. In phase 2, multiple DDEs were recorded for OARs close to the target, mainly involving the stomach, heart, and esophagus. Tumors in the hilum and liver segments I, IV, and VIII were the most common locations for DDEs. On root cause analysis, 3 etiologies of DDE emerged: craniocaudal shift (69.2%), anatomic changes (28.2%), and anteroposterior shifts (2.6%).
OARs close to liver lesions may receive higher doses than expected during SBRT owing to interfractional variations in OARs relative to the target. These differences in planned versus expected dose can lead to toxicity. Efforts to better evaluate OARs with daily image guidance may help reduce risks. Application of adaptive replanning and improved and real-time image guidance could mitigate risks of toxicity, and further study into their applications is warranted.
立体定向体部放射治疗（SBRT）是治疗肝恶性肿瘤的有效方法。然而，对于相邻危及器官（OAR）的分次间剂量变化知之甚少。我们研究了肝 SBRT 患者分次间器官运动和摆位变化对 OAR 剂量的影响。
对 30 例接受肝 SBRT 治疗的患者进行了分析。在每个分次治疗前，采用带轨诊断质量 CT 进行每日图像引导。在第 1 阶段，对 10 例患者的所有 OAR（包括肝脏、心脏、右肾、食管、胃、十二指肠和大肠）进行了每日图像勾画。在第 2 阶段，仅对 20 例靶区附近的 OAR 进行勾画。生成每个每日 CT 的剂量分布，并记录每个 OAR 的每日剂量，并与临床阈值进行比较，以确定是否发生每日剂量超过（DDE）。
在第 1 阶段，观察到 OAR 的计划剂量与实际剂量之间存在显著的分次间剂量差异，但差异很少具有临床意义，仅出现 1 例 DDE。在第 2 阶段，靶区附近的 OAR 记录到多个 DDE，主要涉及胃、心脏和食管。DDE 最常见的部位是肝门和肝段 I、IV 和 VIII 的肿瘤。在根本原因分析中，出现了 3 种 DDE 的病因：头脚移位（69.2%）、解剖变化（28.2%）和前后移位（2.6%）。
由于 OAR 相对于靶区的分次间变化，靠近肝病变的 OAR 可能会接受比预期更高的剂量。这些计划剂量与预期剂量之间的差异可能导致毒性。通过每日图像引导更好地评估 OAR 的努力可能有助于降低风险。应用自适应重计划和改进的实时图像引导可能会降低毒性风险，需要进一步研究其应用。
