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...