What is the absolute maximum lung V20 that you will accept for patients undergoing chemoradiation for locally advanced lung cancer?

Here's how I start with those high V20 plans:

I usually do a 4D CT, then make ITVs. I use a 7mm CTV for primary lung and a 3 mm CTV for nodal disease. Using a Boolean function it's easy to put them together for a CTV6000 and then expand that by 5 mm. We do daily CBCT for alignment and I think 5 mm i...