Changes in dimensions of the rectum are known to affect the position of the prostate with implications for the accuracy of radiotherapy delivery. Current practice involves daily laxative use to empty the rectum prior to treatment. This study examined the effect of bulking and osmotic laxation regimens on reducing rectal gas in patients receiving external beam radiation therapy for prostate cancer.
A single blinded randomised controlled trial was conducted. Participants assigned to the intervention group (IG) were instructed to consume a bulking laxative and probiotic and the standard care group (SC) instructed to consume an osmotic laxative. Both groups followed a standard low gas diet. Rectal gas ratings were determined from cone-beam computed tomography (CBCT) scans. Dietary and laxative compliance, bowel habits, fibre and fluid intakes were determined from food diaries.
Demographic characteristics were not significantly different between the two treatment arms. The mean age was 74 years. Participants were randomised into the IG (n=8) and SC group (n=9). The planned accrual target of 20 was not reached due to time and funding constraints. Analysis of 433 CBCT scans indicate the odds of a higher rectal gas rating were significantly increased for the IG compared with the SC group (OR 3.2, 95% CI 1.77-5.78, p<0.001). Average fibre intake was significantly higher in the IG (p = 0.036), but not a contributing factor to the higher rectal gas levels (OR 1.001, 95% CI 0.92 - 1.09).
The osmotic laxative was more effective at achieving lower rectal gas levels than a bulking laxative with probiotic in this study. Larger studies of commonly used laxatives are required to develop recommendations for bowel preparation during radiotherapy to the prostate.