Proposing a treatment plan strategy for VMAT plans in the event of unavailability of a source linear accelerator or other compatible linacs at a radiotherapy center

Abstract

The study aimed to propose a strategy for dealing with a SIB treatment plan performed using VMAT (Volumetric Modulated Arc Therapy) dynamic technique in the case of unavailability of the source device and no compatible linear accelerator in the center. The study was based on 20 patients with prostate cancer treated with simultaneous integrated boost (SIB) with VMAT treatment plan for two or three full arches. Subsequently, 7-field IMRT (Intensity Modulated Radiation Therapy) replacement plans were made based on the original treatment plans. For the VMAT and IMRT plans, a beam of 6 MeV energy was used with a set dose of 67,5 Gy for PTV (Planning Target Volume) of the prostate and 45 Gy for PTV of the nodes in 30 fractions. The dose differences between VMAT and IMRT technique for PTV volume s did not exceed the acceptable limit - of 2%. For critical organs, the difference in dose was within the tolerance doses described in the report QUANTEC (Quantitative Analyses of Normal Tissue Effects in the Clinic). Conformity index CI (Conformity Index) values for plans in VMAT technique were between 0,53 and 0,58, and for plans in IMRT, between 0,49 and 0,54. The total number of monitor units for the VMAT technique was between 626 and 777 MU, for the IMRT plan the minimum number of MU was 2013 MU, and the maximum was 2766 MU. Studies have shown that for PTV, despite the minor differences obtained for doses in critical organs, while falling within the criteria for tolerable doses and longer irradiation times, the SIB-IMRT technique can be used as an alternative treatment plan for the patient without compromising the quality of treatment.