Sample size, statistical analyses: In the RAPID trial, 88% of patients with Excellent or Good cosmesis prior to RT had Excellent or Good scores at 3 years. Only patients with Excellent/Good cosmesis at baseline will be included in the current study. The proportion of women with Excellent/Good cosmesis at 1 and 2 years will be calculated. Using 80% power, a non-inferiority margin of 0.08 and a one-sided binomial test for non-inferiority and a significance level of 0.05, will require a sample size of 249 women with evaluable 2-yr cosmesis. 274 patients will be recruited to allow for a 10% drop-out rate. To ensure safety, a first interim analysis with Grade 2 or higher breast fibrosis as the primary endpoint, will be conducted when 50 patients have completed their 1-year assessment and repeated when 50 patients have completed their 2-year follow up. If the rate of Grade 2 or higher fibrosis exceeds 5% at either time point, trial accrual will be suspended.