In which scenario would you prefer use of passive scatter proton therapy over intensity modulated proton therapy?

During my fellowship 5 years ago, the training I received was that passive scatter had sharper beam penumbra than pencil beam scanning, due to the use of a brass block (think like an electron cone) closer to the patient.

However, I think that the final margin width or total volume treated is more im...

Proton therapy for choroidal melanoma.

Completely irrelevant to the vast majority in the trenches.