An Investigation of the Dose Distribution Effect Related with Collimator Angle for VMAT Method

Abstract

Aim of this study is to investigate the efficacy of dose distribution in eleven prostate cancer patients with single VMAT and double VMAT when varying collimator angle. We generated optimum single and double VMAT treatment plans when collimator angle was 0 degrees. We recalculated single VMAT plans at different collimator angles(0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, 90 degrees) for double VMAT plans(0 degrees-0 degrees, 15 degrees-345 degrees, 30 degrees-330 degrees, 45 degrees-315 degrees, 60 degrees-300 degrees, 75 degrees-285 degrees, 90 degrees-270 degrees) without changing any optimization parameters. HI, DVH and %95 dose coverage of PTV calculated and analyzed. We determined better dose distribution with some collimator angles. Plans were verified using the 2 dimensional ion chamber array Matrixx (R) and 3 dimensional Compass (R) software program. A higher % 95 dose coverage of PTV was found for single VMAT in the 15 degrees collimator angle, for double VMAT in the 60 degrees-300 degrees and 75 degrees-285 degrees collimator angles. Because of lower rectum doses, we suggested 75 degrees-285 degrees. When we compared single and double VMAT's dose distribution, we had better % 95 dose coverage of PTV and lower HI with double VMAT. Our result was significant statistically. These finds are informative for choosing 75 degrees-285 degrees collimator angles in double VMAT plans for prostate cancer.