Early stopping guidelines/interim futility analysis
An interim futility analysis will be carried out when 1/3 of patients have 6 months follow-up. If the upper 95% confidence limit of the mean difference in 6-months change scores between the treatment arms is less than the pre-specified non-inferiority margins, i.e., < -6 for GU and < -5 for GI, the 2 fraction arm will be deemed inferior to the 5 fraction arm. This is the same interim futility analysis as used in the SHORTER trial [