Dosimetric comparison between using daily cone beam CT and planning CT in Volumetric Modulated Arc Therapy technique for prostate cancer therapy

Abstract

This research aimed to investigate the dosimetric change in target and organs at risk during prostate cancer treatment. Target and critical organs positions in prostate cancer were based on daily CBCT. A total of 220 daily CBCT form five patients who were treated with VMAT technique for 79.2 Gy prescribed dose in 44 fractions were selected. The CTV, PTV, bladder and rectum volumes were manually contoured on daily CBCT images after registered with planning CT. The original plan was transferred and recalculated on daily CBCT images. The DVHs were selected to analyze the dosimetric results. In the result, the percent volume difference at V95% of CTV and PTV were 1.5% ± 3.7% and -6.5% ± 5.0%, respectively. The average volume difference of all V70Gy, V65Gy and V60Gy of daily CBCT and planning CT images showed -21.9% ± 22.6 % and 2.1% ± 51.0% for bladder and rectum, respectively. In conclusion, the dosimetric comparison between using daily cone beam CT and planning CT in VMAT technique for prostate cancer therapy is not significantly different for CTV, in contrast dosimetric difference of the PTV, bladder and rectum are significantly changed.