DOSIMETRIC COMPARISON OF VMAT AND 3D CONFORMAL RADIOTHERAPY IN PREOPERATIVE RECTAL CANCER

The standard procedure in treating rectum cancer is surgical intervention, but presurgical chemotherapy and radiotherapy lead to a lower rate of localized recidives. Our study compared the results obtained by two techniques of radiation treatment planning (RTP) in radiotherapy, which patients received in the preoperative course of rectum cancer treatment, Volumetric Modulated Arc Therapy (VMAT) and field-in-field three-dimensional conformal radiotherapy (FIF 3D-CRT). We analyzed better coverage of the planning target volume (PTV) and better protection of organs from risk (OAR): bladder, bowel, left femoral head, and right femoral head results and monitor unit (MU). Also, we analyzed the target volume coverage indicators included homogeneity index (HI), and conformity index (CI). Selected five patients were treated in University Clinical Center Kragujevac during 2020. The two types of techniques for making radiotherapy plans, mentioned above, were designed for each patient using the same CT scans. All plans were done on the treatment planning system ECLIPSE- Version 15.6 (Varian). The prescribed dose for all patients was 50 Gy in 25 fractions. The first arc was planned in the clockwise direction and the second in the counter clockwise direction. FIF 3D-CRT plans were obtained by using fields from four different directions with the same isocenter. It was obtained that VMAT plans, compared to the FIF 3D-CRT, achieved better coverage of the PTV (D95%), better heterogeneity, and conformity. Protection for OAR such as the bladder, femoral heads, and small bowel is much better than that given by FIF 3D-CRT plans. However, the number of MU calculated by FIF 3D-CRT is almost twice lower compared to VMAT.