Do you constrain dose to the muscles of mastication in definitive and/or post-op HN RT to lower the risk of trismus?

I don't know of any published data on constraints for masseter or pterygoid. While we are on this topic, DARS - a phase III randomised multicentre study of dysphagia- optimised (Do-IMRT) versus S-IMRT in head and neck cancer showed improved swallowing with sparing of constrictor muscles and should be part of contouring and optimization whenever feasible.

My practice has been to constrain the lateral pterygoids when treating in the vicinity. There are 4 muscles of mastication. The evidence on which is most responsible for radiation-associated trismus has been mixed and retrospective (MD Anderson Head and Neck Cancer Symptom Working Group, Rao et al., PMID 25920361). But conceptually, the lateral pterygoids seem most at risk. While the masseters, temporalis, and medial pterygoids all work to elevate the mandible, the lateral pterygoids bear the so...