A study of segment weight optimization with the CMS XiO step-and-shoot IMRT technique for prostate cancer.

The aim of this study was to compare IMRT optimization in the CMS XiO radiotherapy treatment planning system, with and without segment weight optimization. Twenty-one prostate cancer patients were selected for this study. All patients were initially planned with step-and-shoot IMRT (S-IMRT). A new plan was then created for each patient by applying the segment weight optimization tool (SWO-IMRT). Analysis was performed on the (SWO-IMRT) and (S-IMRT) plans by comparing the total number of segments, monitor units, rectal and bladder dose. The study showed a statistically significant reduction in the total number of segments (mean: 25.3%; range: 16.8%-31.1%) with SWO-IMRT as compared to S-IMRT (p < 0.0001). Similarly, a mean reduction of 3.8% (range: 0.4%-7.7%) in the total MU was observed with SWO-IMRT (p < 0.0001). The study showed an average rectal dose decrease of 13.7% (range: 7.9%-21.4%) with SWO-IMRT (p < 0.0001). We also observed a statistically significant reduction of 26.7% (range: 16.0%-41.4%; p < 0.0001) in the mean dose to the posterior one-third rectum and an overall reduction in mean bladder dose of 2.2% (range: 0.1%-6.1%) for SWO-IMRT (p < 0.0001). This study shows that the segment weight optimization method significantly reduces the total number of segments and the dose to the rectum for IMRT prostate cancer. It also resulted in fewer monitor units for most of the prostate cases observed in this study.