What approach do you take to determine dose constraints for conventionally fractionated reirradiation of the head and neck?

Great question, very challenging scenario.

In general, try to minimize the margins for re-RT, and use IGRT, especially if you are close to the neurologic critical structures. (Optics, brainstem, spinal cord, plexus, temporal lobe.)

Specific doses and whether you exceed limits: that really depends on w...

I wanted to highlight here the 2022 Radium Society AUC document which does contain an attempt at DVH criteria used in the fractionated re-irradiation setting identified during a systematic review.

I try to give full dose if treating for cure, e.g. 70 Gy. I like hyperfractionation as a way to separate the late and acute side effect curves, e.g., 72 Gy in 60 fx BID with cetuximab like Bonner trial. I use the Carsten Nieder constraints for spinal cord, which have 3 key components:

1. Over 6 months ...