Ninety-degree angled collimator: a dosimetric study related to dynamic intensity-modulated radiotherapy in patients with endometrial carcinoma

Abstract

Background Our purpose was to ensure that the dose constraints of the organs at risk (OARs) were not exceeded while increasing the prescription dose to the planning target volume (PTV) from 45 Gy to 50.4 Gy with the dynamic intensity-modulated radiotherapy (IMRT) technique. While trying for this purpose, a new dynamic IMRT technique that named 90° angled collimated dynamic IMRT (A-IMRT) planning was developed by us. Methods This study was based on the computed tomography data sets of 20 patients with postoperatively diagnosed International Federation of Gynecology and Obstetrics stage 2 endometrial carcinoma. For each patient, conventional dynamic IMRT (C-IMRT, collimator angle of 0° at all gantry angles), A-IMRT (collimator angle of 90° at gantry angles of 110°, 180°, 215°, and 285°), and volumetric modulated arc therapy (VMAT) were planned. Planning techniques were compared with parameters used to evaluate PTV and OARs via dose-volume-histogram analysis using the paired two-tailed Wilcoxon’s signed-rank test; p < 0.05 was considered indicative of statistical significance. Results All plans achieved adequate dose coverage for PTV. Conformality was best obtained with VMAT, whereas homogeneity was best obtained with C-IMRT. The conformality of A-IMRT was inferior to the conformality of C-IMRT; A-IMRT had similar homogeneity to VMAT. The bone marrow dose constraint was exceeded in 4 (20%), 16 (80%), and 18 (90%) patients with VMAT, A-IMRT, and C-IMRT, respectively. The bladder dose constraint was exceeded in no patients with A-IMRT or VMAT, but it was exceeded in 19 (95%) patients with C-IMRT. Dose constraints of the rectum and bilateral femoral heads were exceeded in no patients with A-IMRT or VMAT, but they were exceeded in 20 (100%) patients with C-IMRT. The dose constraint of the bowel (for V40 as in the RTOG 0418 trial) was exceeded in 4 (20%), 5 (25%), and 8 (40%) patients with VMAT, A-IMRT, and C-IMRT, respectively. Conclusions OARs are better protected when external beam radiotherapy is applied to the pelvis at a dose of 50.4 Gy by turning the collimator angle to 90° at some gantry angles with the dynamic IMRT technique in the absence of VMAT.

Comparing treatment plans for stomach cancer: three-dimensional conformal radiotherapy (3D-CRT), physical wedge-based conformal RT (WB-CRT) and intensity-modulated radiotherapy (IMRT)

“…In another study, Serarslan and colleagues compared the dosimetric differences using physical WB-CRT, field-in-field IMRT and IMRT. 15 Techniques were evaluated with respect to expected target volume coverage and the dose to OAR. They suggested that IMRT was superior to WB-CRT ( p = 0·005 for the V 20 for the right kidney; p = 0·001 for the D-mean in the left kidney; p = 0·023 for the V 20 for the left kidney).…”

“…CI is defined by a ratio of reference isodose volume to target volume of PTV. 15 The value of CI varies between 0 and 1, and a value closer to one indicates better conformity of dose to the PTV. The 95% isodose volume was taken as the reference volume of the PTV.…”