What is the longest treatment break you would allow during definitive HN RT +/- chemo?

Continuing therapy after a break depends on several factors. The timing of the break is important: Little repopulation occurs in the first 3-4 weeks of standard RT, and then it quickly accelerates, with a loss in local control rates of of 14%, 26%, and 35% after 1,2 and 3 week breaks respectively (Withers HR Acta Oncol 1988). Consequentially, between the 5^th and 7^th week of RT, an average of 0.5-0.7 Gy is lost daily to repopulation. Thus, a short break before 4 weeks may have few consequences, while a longer break requires an adjustment. There are several ways to adjust, such that a 1 or 2 week break may require altering the rest of the therapy course by acceleration or hypofractionation taking into account the total BED. For example, a 2 w...