Predicting patient-specific prostate motion using pelvic fat and pelvic cavity volume for prostate radiotherapy

Background:The prediction of prostate motion is important for matching planned and delivered dose distributions in prostate radiotherapy.This study aimed to assess the relationship between anatomical characteristics and inter-and intra-fraction prostate motion.Materials and Methods: Sixty-six patients who underwent fiducial marker implantation were retrospectively evaluated.The anatomical characteristics (subcutaneous adipose tissue thickness, pelvic cavity volume, and fat volume of the lesser pelvis around the prostate), inter-and intra-fraction prostate motion, and standard deviations (SDs) in the anterior-posterior (AP), superior-inferior (SI), and leftright (LR) directions were determined, and their correlations were analyzed.Additionally, the three-dimensional (3D) distance between the coordinates of the center of gravity of the prostate and inferior margin of the symphysis pubis was calculated.Results: The pelvic cavity volume around the prostate exhibited a moderate correlation with the SD for inter-fraction prostate motion in the LR direction (r=0.47) and that for intra-fraction prostate motion in the AP and LR directions (r = 0.41, 0.52).The 3D distance between the coordinates of the center of gravity of the prostate and inferior margin of the symphysis pubis showed a moderate correlation with the average inter-fraction prostate motion in the AP direction (r=0.46).Conclusion: Prostate motion in the AP and LR directions may be related to the fat and pelvic cavity volumes around the prostate.The evaluation of anatomical characteristics can help predict patient-specific prostate motion during treatment planning.