What is the role of MRI in target delineation of radiation therapy for non-NPC H&N cancers?

I don't think MRI is necessary for most OPCs. I do use MRI in some cases, such as 1) patients being considered for surgery first (to determine if endophytic tumor is better suited for RT), 2) whenever I have clinical concern for perineural spread, and 3) to further assess deep invasion or involvement of adjacent structures that may not be so obvious on CT with contrast or PET/CT, such as an endophytic base of tongue cancer with sublingual gland involvement or nerve involvement, or a to better see a small soft palate cancer. MRI is superior to both for soft tissue delineation and perineural spread assessment.

That said, I do believe that the vast majority of OPCs can be treated with good CT neck with contrast + FDG-PET/CT. Would generally re...

Our practice is to obtain MRI for all oropharynx cancers planned for radiation. PET/CT often underestimates the size of the primary tumor. Pictures in the supplement of our paper illustrate how PET/CT can underestimate the GTV compared to MRI.

Tsai et al., PMID 35050342