Would you add dose/fractions to a post-mastectomy patient who had a two week break due to being COVID-19 positive?

There are no data on how treatment breaks impact the effectiveness of PMRT. I doubt a two-week break has a substantial impact in the era of effective systemic therapy, particularly if hypofractionation is used. Having said that, I do tend to add 1 or 2 fractions when there is a treatment break or breaks resulting in more than 2 weeks beyond the initially anticipated completion of PMRT. This likely has minimal effect on the risk of complications, though again, there are very few data on that subject.