What dose constraints do you use when treating a patient with bilateral breast cancer with RNI?
This article highlights lung, heart, esophagus, and dose homogeneity constraints we aim for when treating bilateral breast cancer and RNI.
Bilateral breast/chest wall irradiation with regional nodal irradiation (RNI) is one setting in which the dosimetric advantages of proton therapy are particularly pronounced (Mutter et al., PMID 34048815; Garda et al., PMID 35647397). In our health system, these patients are routinely referred for pencil-beam scanning proton therapy. With contemporary planning, we can typically achieve a mean heart dose of <0.7–1 Gy and a bilateral lung V40% (i.e., V20 Gy for a 50 Gy prescription, V16 Gy for a 40 Gy/15 fraction hypofractionation schedule) of <12–15%, while maintaining comprehensive and robust IMN coverage.
Careful attention to skin dose is an important component of treatment planning. We routinely use a 3-mm skin rind as an optimization structure, with skin constraints individualized based on each patient's risk profile. In patients with unilateral, non-inflammatory breast cancer treated with PMRT, we recently reported comparable patient- and provider-reported acute skin toxicity with photons and contemporary, well-planned proton therapy (Gergelis et al., PMID 42269789).
I look at each side individually and try to plan to meet ipsilateral lung constraints and delete contralateral lung constraints given bilateral. I also counsel patients on potential increased lung toxicity in these situations.
If treating bilateral IMNs, 3D-CRT is often very difficult, and I switch to IMRT/VMAT.