When treating patients with hypofractionated radiation to the breast in 16 fractions do you typically treat 4 or 5 days a week?

We treat 5 days a week which was the standard in the Whelan randomized trial that compared this fractionation scheme to conventional fractionation (https://www.ncbi.nlm.nih.gov/pubmed/20147717). In the START B trial, 15 fractions (total dose 40 Gy) were given also in 5 consecutive days (https://www....