Medical Laboratory Techniques Department, AL-Maarif University College, Anbar, Iraq.
Manipur International University, Imphal, Manipur, India.
J Xray Sci Technol. 2024;32(5):1331-1348. doi: 10.3233/XST-240172.
Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are the main radiotherapy techniques for treating and managing rectal cancer. Collimator rotation is one of the crucial parameters in radiotherapy planning, and its alteration can cause dosimetric variations. This study assessed the effect of collimator rotation on the dosimetric results of various IMRT and VMAT plans for rectal cancer.
Computed tomography (CT) images of 20 male patients with rectal cancer were utilized for IMRT and VMAT treatment planning with various collimator angles. Nine different IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six different VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. The dosimetric results of various treatment techniques for target tissue (conformity index [CI] and homogeneity index [HI]) and organs at risk (OARs) sparing (parameters obtained from OARs dose-volume histograms [DVH]) as well as radiobiological findings were analyzed and compared.
The 7-fields IMRT technique demonstrated lower bladder doses (V40Gy, V45Gy), unaffected by collimator rotation. The 9-fields IMRT and 2-arcs VMAT (excluding the 90-degree collimator) had the lowest V35Gy and V45Gy. A 90-degree collimator rotation in 2-arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90-degree rotation had adverse effects on small bowel NTCP (normal tissue complication probability). No superiority was found for a 45-degree collimator rotation over 0 or 30 degrees in VMAT techniques.
Collimator rotation had minimal impact on dosimetric parameters in IMRT planning but is significant in VMAT techniques. A 90-degree rotation in VMAT, particularly in a 2-full arc technique, adversely affects PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes.
调强放疗（IMRT）和容积旋转调强放疗（VMAT）是治疗和管理直肠癌的主要放疗技术。准直器旋转是放疗计划中的关键参数之一，其改变会导致剂量学变化。本研究评估了准直器旋转对直肠癌各种调强放疗和容积旋转调强放疗计划的剂量学结果的影响。
利用 20 名男性直肠癌患者的 CT 图像，为每位患者进行不同准直器角度的调强放疗和容积旋转调强放疗计划。为每位患者规划了 9 种不同的调强放疗技术（5、7 和 9 个共面野，准直器角度为 0°、45°和 90°）和 6 种不同的容积旋转调强放疗技术（1 和 2 个全共面弧，准直器角度为 0°、45°和 90°）。分析和比较了各种治疗技术的靶组织（适形指数[CI]和均匀性指数[HI]）和危及器官（OARs）保护（从 OARs 剂量-体积直方图[DVH]获得的参数）的剂量学结果以及放射生物学发现。
7 野调强放疗技术显示较低的膀胱剂量（V40Gy、V45Gy），不受准直器旋转影响。9 野调强放疗和 2 弧容积旋转调强放疗（不包括 90°准直器）的 V35Gy 和 V45Gy 最低。2 弧容积旋转调强放疗中 90°准直器的旋转显著增加小肠和膀胱 V45Gy、股骨头剂量和 HI 值。放射生物学方面，90°旋转对小肠 NTCP（正常组织并发症概率）有不利影响。在容积旋转调强放疗技术中，45°准直器旋转没有优于 0 度或 30 度。
准直器旋转对调强放疗计划的剂量学参数影响较小，但在容积旋转调强放疗技术中影响较大。VMAT 技术中 90°旋转会显著降低 PTV 均匀性指数、膀胱剂量和小肠 NTCP。评估的其他准直器角度对 VMAT 剂量学和放射生物学结果没有显著影响。
