How would you define the primary site GTV and CTV volumes in a high risk neuroblastoma patient who obtained a complete response to induction chemo?

This scenario is exceedingly rare.

My opinion would probably depend on staging/histology/MYCN status. Some of the historic HR NBL cases are now being shifted into Intermediate Risk and there have been favorable outcomes without the routine use of RT.

So if it was a Stage 3 365-547d, MYCN-NA, UH, any ploidy

OR a Stage 4, 365-547d, MYCN-NA, FH, DI<1 then

with a CR - you could make the argument to omit RT and even discuss whether the patient should be treated with an HR paradigm, to begin with.

If ...