20% ok. Tell us about the 80%. Early stage breast, prostate?
You are correct, a lot of places are treating whomever walks in the door, but this also happens in Xray centers. For those in proton only facilities, they have no other in-house option, and vice-versa for Xray centers, so I try not to judge too harshly. We are all doing the best we can with what we have. I am really fortunate to have both options for my patients, who are the ultimate beneficiaries of what we do.
I do use protons for early stage breast cancer, typically for patients who meet the 2023 ASTRO guideline, e.g. under age 40 (2nd malignancy risk) and/or left-sided breast CA if I'm unable to meet heart constraints despite using DIBH, prone, or a heart block. On a clinical trial is another indication for early stage breast CA.
Heart constraints have gotten a lot stricter lately after the paper by Zureick, et al, in the Red Journal. Cardiac mean dose on the order of 1 Gy and LAD mean dose of 3 Gy are not easy to meet, but predict for major adverse Cardiac events at 4 years post tx. This was a bit of a surprise to me, as I thought those changes would take decades to show up.
I have used protons for early stage prostate on COMPPARE trial, but only rarely off protocol. I usually tell patients that there isn't much difference between a good IMRT plan for prostate-only dz and an average proton plan. Especially with a good SPACEOAR, but I know that is a controversial topic here.
I do see a big improvement in bowel and bladder midline sparing for prostate when treating pelvic nodes with IMPT as compared to IMRT. Treating involved pelvic and para-aortic nodes is part of the ASTRO 2023 recommendactions, which makes sense to me because usually I'm trying to give 70+ Gy to gross dz but the bowel tolerance is closer to 50.
I have treated a couple patients with ulcerative colitis who were medically inoperable using protons, due to the better bowel sparing, but still felt pretty nervous about it. There's lot of scenarios where we simply don't know until we make the comparison plans.