Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands.
Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands.
Int J Radiat Oncol Biol Phys. 2019 Dec 1;105(5):1151-1159. doi: 10.1016/j.ijrobp.2019.08.052. Epub 2019 Aug 30.
To evaluate the feasibility of fiducial markers as a surrogate for gross tumor volume (GTV) position in image-guided radiation therapy of rectal cancer.
We analyzed 35 fiducials in 19 patients with rectal cancer who received short-course radiation therapy or long-course chemoradiation therapy. Magnetic resonance imaging examinations were performed before and after the first week of radiation therapy, and daily pre- and postirradiation cone beam computed tomography scans were acquired in the first week of radiation therapy. Between the 2 magnetic resonance imaging examinations, the fiducial displacement relative to the center of gravity of the GTV (COG) and the COG displacement relative to bony anatomy were determined. Using the cone beam computed tomography scans, inter- and intrafraction fiducial displacement relative to bony anatomy were determined.
The systematic error of the fiducial displacement relative to the COG was 2.8, 2.4, and 4.2 mm in the left-right, anterior-posterior (AP), and craniocaudal (CC) directions, respectively. Large interfraction systematic errors of up to 8.0 mm and random errors up to 4.7 mm were found for COG and fiducial displacements relative to bony anatomy, mostly in the AP and CC directions. For tumors located in the mid and upper rectum, these errors were up to 9.4 mm (systematic) and 5.6 mm (random) compared with 4.9 mm and 2.9 mm for tumors in the lower rectum. Systematic and random errors of the intrafraction fiducial displacement relative to bony anatomy were ≤2.1 mm in all directions.
Large interfraction errors of the COG and the fiducials relative to bony anatomy were found. Therefore, despite the observed fiducial displacement relative to the COG, the use of fiducials as a surrogate for GTV position reduces the required margins in the AP and CC directions for a GTV boost using image-guided radiation therapy of rectal cancer. This reduction in margin may be larger in patients with tumors located in the mid and upper rectum compared with the lower rectum.
评估在直肠癌图像引导放疗中，使用基准标记物作为大体肿瘤体积（GTV）位置的替代物的可行性。
我们分析了 19 例接受短程放疗或长程放化疗的直肠癌患者的 35 个基准标记物。在放疗前和放疗后第一周进行磁共振成像检查，并在放疗第一周每天进行放疗前和放疗后锥形束计算机断层扫描。在两次磁共振成像检查之间，确定基准标记物相对于 GTV 重心（COG）的位移和 COG 相对于骨性解剖结构的位移。使用锥形束计算机断层扫描，确定基准标记物相对于骨性解剖结构的内外分位移。
基准标记物相对于 COG 的系统误差在左右、前后（AP）和头尾（CC）方向分别为 2.8、2.4 和 4.2mm。COG 和相对于骨性解剖结构的基准标记物的大界面系统误差高达 8.0mm，随机误差高达 4.7mm，主要在 AP 和 CC 方向。对于位于中直肠和上直肠的肿瘤，这些误差分别高达 9.4mm（系统）和 5.6mm（随机），而对于下直肠的肿瘤，这些误差分别为 4.9mm 和 2.9mm。所有方向的内部分位移的系统误差和随机误差均≤2.1mm。
发现 COG 和相对于骨性解剖结构的基准标记物的大界面误差。因此，尽管观察到了相对于 COG 的基准标记物的位移，但在使用图像引导放疗治疗直肠癌时，使用基准标记物作为 GTV 位置的替代物，会减少在 AP 和 CC 方向上对 GTV 进行增强治疗所需的边缘。与下直肠相比，位于中直肠和上直肠的肿瘤患者的这种边缘减少可能更大。
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