What is the consensus on the size of the expansion from the gross tumor volume (CTV) to the clinical target volume (PTV) in treating intact supraglottic squamous cell carcinoma with radiotherapy?

The modern approach for head and neck cancer, based on international guidelines, has been CTV high dose (70 Gy) = GTV + 5 mm expansion (respecting anatomic boundaries and structures not at risk). Some centers in the past and present have also had an intermediate volume where an additional 5mm is add...

I have used primary tumor GTV (using input from the ENT surgeon and the largest volume noted on imaging; PET (except T1 or small T2), diagnostic HN CT with contrast, and MRI) + 5 mm = CTV, then CTV + 3 mm = PTV, Chen et al., PMID 20932680. I found consensus guidelines based on primary tumor subsites...