This is an area of active clinical trial development esp. as it relates to immunotherapy concurrent with SBRT. That being said, we certainly have phase I, II, and preliminary phase III data suggesting that SBRT in the setting of recurrent disease is safe and may offer extended LR control rates in a ...

I don’t use SBRT to re-irradiate head and neck cancer. Out of field failure is very likely. 

I agree with @Christian Hyde - there still seems to be a role for fractionation in recurrent HNC. These are still typically low a/b ratio tumors (if we are still using that concept), the tissue around it has typically received substantial doses, and there is some data with BID RT. The SBRT experien...

When reirradiating for cure with squamous cell CA or small cell CA (fast growing tumors), I generally avoid large fractions because of a desire to maximize the alpha-beta BED calcs for the tumor and minimize it for normal tissue. Small fractions tend to help this, and hyper fractionation has a well ...