If using protons instead of photons, does the use of protons impact your recommendation for using hypofractionation in breast cancer?
I work at Mayo in Rochester, and we have a busy proton breast practice. We routinely use moderate hypofractionation for non-reconstructed or intact breast patients treated with protons. We also have initiated and enrolled a number of patients on hypofractionation trials with our Arizona colleagues, which are in various stages of completion/presentation/publication. For example, @Dr. First Last also presented our randomized 15 vs 25 fraction PMRT trial at SABCS last year -- this included reconstructed patients and the publication is forthcoming. We also reported initial results of an ultra-hypofractionated vs moderate hypofractionated whole breast intact trial at ASTRO last year, including both protons and photons.
Ultimately, I think hypofractionation is a nice way to treat when choosing protons, though, like all recon PMRT patients, there are fewer data with regard to potential impact on reconstructive/cosmetic outcomes. As a result, I discuss both conventional and moderate hypofractionation for reconstructed patients and guide recommendations via shared decision making. We also currently have an ultra-hypofractionation PMRT/RNI randomized trial ongoing.
Like Dr. @Dr. First Last notes above, one of the key factors regarding acute proton skin toxicity is skin dose. We have also reported a comparison of skin doses and reactions achieved with IMPT vs photon based PMRT, and we did not see a brisker skin reaction with protons. However, we are pretty intentional about not inadvertently escalating the skin dose/toxicity. We do contour the skin as a structure, both for evaluation of dose coverage and pushing out hot spots (PMRT), and to try to reproduce a surface dose that is more akin to photons for intact patients, particularly important for early stage - lower risk (like the intact breast whole breast study patients). These patients can generally expect a high chance of good to excellent cosmesis with photon approaches and careful attention to planning with proton is needed to ensure similar outcomes.
We have been using the Canadian hypofractionated RT regimen for whole breast at our proton center since 2016 when indicated. We typically modulate the dose 5 mm off the skin (100% IDL 5 mm in). In general, have not noticed any major difference in skin side effects with this approach compared to photons. I have not considered the FAST-Forward regimen with protons.
No, it does not. We have offered hypofrac routinely to women with unreconstructed chest wall or intact breast who are recommended for proton therapy, need RNI, and not participating in RADCOMP. We most often use the UK START B 40 Gy/15 fractions.
We continue to recommend patients participate on the RADCOMP randomized trial, which only needs about 100 more patients. Hypofractionation is not permitted on RADCOMP.
Mayo has published on a series of patients with proton PMRT and immediate reconstruction, some of which had hypofractionated treatment.