Evaluation of prostate movement trend using individual patient anatomical information for prostate volumetric modulated arc therapy.

Organ movement during prostate cancer radiotherapy can significantly impact treatment accuracy. This study aimed to investigate the relationship of prostate movement during the treatment period with pretreatment patient anatomical information. A total of 103 patients with prostate cancer who underwent volumetric modulated arc therapy (VMAT) were included. Lesser pelvis space around the prostate and prostate volumes were contoured and measured using a radiotherapy treatment planning system (RTPS) and classified into 2 groups (< median, ≧ median). The median and standard deviation (SD) inter- and intra-fraction prostate movement during treatment was calculated in the anterior-posterior (AP), left-right (LR), and superior-inferior (SI) directions, and the correlation for anatomical information was analyzed. Statistical significance testing and percentile analysis were utilized to assess the inter- and intra-fraction prostate movement of 2 groups based on the parameters above. Significant differences in prostate volume (inter: AP, LR, and SI) were observed between the 2 groups. The SD of inter- and intra-fraction prostate movement in the LR direction exhibited low positive correlations with lesser pelvis space around the prostate and prostate volume (r > 0.3). In the 5th to 95th percentile range of prostate movement, patients with a prostate volume ≧ 30 mL showed an increase of >10% (inter: AP, SI, LR). These findings suggest that pelvic space around the prostate and prostate volume are correlated with prostate movement during radiotherapy, indicating their importance in optimizing prostate margins in treatment planning.