Evaluation of a Protocol to Reduce Rectal Volume and Prostate Motion for External Beam Radiation Therapy of the Prostate

Purpose: To assess the impact of an empty rectum protocol on prostate movement at the time of radiation treatment delivery and the effect of such a protocol on bowel habits. Methods and Materials: Thirty-two patients were implanted with three fiducial markers before radiation treatment planning. Fifteen patients were instructed to follow an empty rectum protocol (ERP) for both treatment planning and delivery, whereas 17 patients received no rectal preparation instructions. Both prostate movement data and the time between the patients' last bowel movement and the treatment appointment time were collected for all patients throughout treatment. Before the delivery of radiation, daily electronic portal images were taken of the anterior and right lateral fields. Positional errors of greater than 3 mm were corrected before treatment commenced. Results: Differences in isocenter position between planned field placement and actual field placement (before corrective action) were compared. Analysis of directional displacement showed a statistically significant trend for the prostate to be more likely to be shifted inferior and left (P < .001 and P = .0004), regardless of use of ERP. Patients not on the ERP tended to have less displacement in the right direction (P = .054). Patients on the ERP had larger displacements in the inferior direction (P = .02) and tended to have larger displacements over the course of treatment (P = .04). There was no statistically significant trend in the anteroposterior direction. Time lapse between last bowel movement and treatment was not significantly different between the two groups. The ERP group mean was 3.9 hours (95% CI 3.4, 4.4) compared with the non-ERP group mean of 3.8 hours (95% CI 3.4, 4.3). Time since last bowel movement did not have an impact on prostate position. Conclusion: Prostate displacement evaluated in this study is similar to that found by others. The empty rectum protocol used in this study has some impact on prostate displacement in some dimensions, but overall does not reduce the variability of prostate position or have an influence on patients' bowel habits.