Division of Clinical Radiology Service, Kyoto University Hospital, 54 Kawaharacho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
Department of Information Technology and Medical Engineering, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Kawaharacho, Shogoin, Sakyo-ku, Kyoto 606-8397, Japan.
J Radiat Res. 2023 Jul 18;64(4):711-719. doi: 10.1093/jrr/rrad048.
The purpose of this study was to retrospectively assess target localization accuracy across different soft-tissue matching protocols using cone-beam computed tomography (CBCT) in a large sample of patients with pancreatic cancer and to estimate the optimal margin size for each protocol. Fifty-four consecutive patients with pancreatic cancer who underwent 15-fraction volumetric modulated arc therapy under the end-exhalation breath-hold condition were enrolled. Two soft-tissue matching protocols were used according to the resectability classification, including gross tumor volume (GTV) matching for potentially resectable tumors and planning target volume (PTV) matching for borderline resectable or unresectable tumors. The tolerance of the target localization error in both matching protocols was set to 5 mm in any direction. The optimal margin size for each soft-tissue matching protocol was calculated from the systematic and random errors of the inter- and intrafraction positional variations using the van Herk formula. The inter- and intrafraction positional variations of PTV matching were smaller than those of GTV matching. The percentage of target localization errors exceeding 5 mm in the first CBCT scan of each fraction in the superior-inferior direction was 12.6 and 4.8% for GTV and PTV matching, respectively. The optimal margin sizes for GTV and PTV matching were 3.7 and 2.7, 5.4 and 4.1 and 3.9 and 3.0 mm in the anterior-posterior, superior-inferior and left-right directions, respectively. Target localization accuracy in PTV matching was higher than that in GTV matching. By setting the tolerance of the target localization error, treatment can be successful within the planned margin size.
本研究旨在回顾性评估使用锥形束 CT（CBCT）在大量胰腺癌患者中不同软组织匹配方案的靶区定位准确性，并估计每种方案的最佳边缘大小。纳入了 54 例在呼气末屏气条件下接受 15 次容积调强弧形治疗的胰腺癌连续患者。根据可切除性分类，使用两种软组织匹配方案，包括对潜在可切除肿瘤的大体肿瘤体积（GTV）匹配和对边界可切除或不可切除肿瘤的计划靶区（PTV）匹配。两种匹配方案中靶区定位误差的容差均设定为 5mm 方向。使用 van Herk 公式，从分次内和分次间位置变化的系统和随机误差计算每种软组织匹配方案的最佳边缘大小。PTV 匹配的分次内和分次间位置变化小于 GTV 匹配。在每个分次的首次 CBCT 扫描中，超过 5mm 的靶区定位误差的百分比在 GTV 和 PTV 匹配中分别为 12.6%和 4.8%。GTV 和 PTV 匹配的最佳边缘大小分别为 3.7 和 2.7、5.4 和 4.1、3.9 和 3.0mm，在前后、上下和左右方向上。PTV 匹配的靶区定位精度高于 GTV 匹配。通过设定靶区定位误差的容限，可以在计划的边缘大小内成功进行治疗。
