UNASSIGNED: 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.
UNASSIGNED: 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.
UNASSIGNED: 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.
■将20名男性直肠癌患者的计算机断层扫描(CT)图像用于各种准直器角度的IMRT和VMAT治疗计划。九种不同的IMRT技术(准直器角为0°的5、7和9共面场,45°,和90°)和六种不同的VMAT技术(准直器角度为0°的1和2个全共面弧,45°,和90°)为每位患者计划。分析并比较了靶组织(符合性指数[CI]和均匀性指数[HI])和危险器官(OARs)保留(从OARs剂量-体积直方图[DVH]获得的参数)以及放射生物学结果的各种治疗技术的剂量测定结果。
■7场IMRT技术显示出较低的膀胱剂量(V40Gy,V45Gy),不受准直器旋转的影响。9场IMRT和2弧VMAT(不包括90度准直器)具有最低的V35Gy和V45Gy。2弧VMAT中的90度准直器旋转显着增加了小肠和膀胱V45Gy,股骨头剂量,和HI值。放射生物学,90度旋转对小肠NTCP有不良影响(正常组织并发症概率).在VMAT技术中,45度准直器旋转超过0或30度没有发现优越性。
■准直器旋转对IMRT计划中的剂量测定参数影响最小,但在VMAT技术中意义重大。在VMAT中旋转90度,特别是在双弧技术中,对PTV均匀性指数产生不利影响,膀胱剂量,和小肠NTCP。其他评估的准直器角度没有显着影响VMAT剂量或放射生物学结果。