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?

Patient developed pembrolizumab-related pneumonitis after ddAC followed by Taxol/Keytruda - what thresholds/constraints would you prioritize with regard to mean lung, V20, total lung in a patient with prior pneumonitis?

2 Answers

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Radiation Oncology · Varian Medical Systems/Allegheny health network

Answered on

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

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Radiation Oncology · Vanderbilt-Ingram Cancer Center

Answered on

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 feasible, understanding that there is essentially zero data to actually support. Perhaps omission of IMCs is warranted if outer quadrant tumor with N1a disease. Despite recent discussions about whether proton therapy is warranted in breast cancer patients, this may be a patient to evaluate if it would sufficiently lower V20.

I say that as someone who does not "believe" in "routine use of protons" for breast cancer.