The Influence of a Dietary Protocol on Cone Beam CT–Guided Radiotherapy for Prostate Cancer Patients

Purpose To evaluate the influence of a dietary protocol on cone beam computed tomography (CBCT) image quality, which is an indirect indicator for short-term (intrafraction) prostate motion, and on interfraction motion. Image quality is affected by motion ( e.g., moving gas) during imaging and influences the performance of automatic prostate localization on CBCT scans. Methods and Materials Twenty-six patients (336 CBCT scans) followed the dietary protocol and 23 patients (240 CBCT scans) did not. Prostates were automatically localized by using three dimensional (3D) gray-value registration (GR). Feces and (moving) gas occurrence in the CBCT scans, the success rate of 3D-GR, and the statistics of prostate motion data were assessed. Results Feces, gas, and moving gas significantly decreased from 55%, 61%, and 43% of scans in the nondiet group to 31%, 47%, and 28% in the diet group (all p < 0.001). Since there is a known relation between gas and short-term prostate motion, intrafraction prostate motion probably also decreased. The success rate of 3D-GR improved from 83% to 94% ( p < 0.001). A decrease in random interfraction prostate motion also was found, which was not significant after Bonferroni's correction. Significant deviations from planning CT position for rotations around the left-right axis were found in both groups. Conclusions The dietary protocol significantly decreased the incidence of feces and (moving) gas. As a result, CBCT image quality and the success rate of 3D-GR significantly increased. A trend exists that random interfraction prostate motion decreases. Using a dietary protocol therefore is advisable, also without CBCT-based image guidance.