Comparison of volumetric-modulated arc therapy and intensity-modulated radiation therapy prostate cancer plans accounting for cold spots Abstract This study compared dosimetric indices of volumetric-modulated arc therapy (VMAT) with intensity-modulated radiation therapy (IMRT) accounting for cold spots in prostate cancer plans. IMRT plans were retrospectively generated from 30 prostate cancer patients with ten cases for each risk group, who received VMAT plans. The mean, maximum, and minimum doses, and conformity and homogeneity indexes were evaluated for planning target volume (PTV) and the mean dose and V20–V70 for organs at risk (OAR) including the rectum, bladder, right and left femoral heads, and rectum overlapped with PTV (ROP) regions. The numbers and volume percentages of cold spots within PTVs and ROP regions were measured using in-house software. Three-dimensional probabilistic distributions of the probability and distributions of cold spots were generated using a centroid matching technique for visualization and analysis. There was a statistically better dose conformity in the PTV, rectum, and bladder dose-sparing in VMAT compared to that in the IMRT plans, whereas VMAT had statistically worse target dose homogeneity, and right and left femoral head dose-sparing than those of the IMRT plans. The average volume percentage of cold spots per PTV for the VMAT was 4.37 ± 2.68%, which was smaller than the 5.72 ± 1.84% observed for IMRT plans (P = 0.007). The volume percentage of cold spots per ROP for the VMAT did not significantly differ from those for the IMRT plans. Compared with IMRT, the VMAT plans achieved better PTV dose conformity, OAR dose-sparing, and smaller cold spots in the treatment of prostate cancer.