A measured drink of water before pelvic radiotherapy, and bowel preparation kept to what trials support

Why it matters. During pelvic radiotherapy the prostate, cervix or bladder sits between two organs that fill and empty. A fuller bladder lifts bowel out of the field, and a full rectum pushes the prostate forward, so departments give drinking and bowel instructions. They vary widely, and some are more burdensome than the evidence supports.

Bladder. A randomised trial of 110 men compared drinking 540 millilitres (three cups) with 1,080 millilitres (six cups) before planning and each treatment. Bladder volume varied less in the 540-millilitre arm (median variation 76 against 105 millilitres, p equals 0.003), larger bladders at planning went with larger variation later, and toxicity, comfort and quality of life did not differ. A meta-analysis of ten cohort studies and one randomised trial with 417 men found that 300 to 400 millilitres gave the best reproducibility and that larger volumes, including drinking until the bladder felt full, gave less.

Bowel. In a randomised trial of 78 men, adding an anti-wind medicine to bowel preparation did not reduce rescans at planning or rectal diameter during treatment; the authors suggested the standardised education given to both arms may have been enough. Another randomised trial, of 30 men, found simethicone did not reduce rectal or gas volume overall. A randomised trial in 17 men found an osmotic laxative left less rectal gas than a bulking laxative with a probiotic. The direction is that simple, consistent instructions matter more than added medicines, and no trial has shown a bowel regimen improves toxicity.

Adoption is not measured: OnCo found no survey of drinking or bowel instructions across radiotherapy departments.