What dose constraints for lung would you use in a patient with breast cancer requiring regional nodal irradiation who had significant pneumonitis during systemic therapy?

I would look into the absolute benefit of RNI in someone with significant pneumonitis as the downside may outweigh the benefit.

No hard and fast EBM number in this situation given the rarity and paucity of data. V20 < 30-35% still has very low risk of symptomatic pneumonitis in standard patients, and mechanism of pneumonitis development from IT vs RT is different.

That being said, I would probably shoot for V20 < 20-25% as f...