Regional Near-surface Dose Predicts Moist Desquamation and Implant Failure in Patients Receiving Radiation Therapy for Breast Cancer.

Purpose/objective: We correlated regional near-surface dose with toxic effects and implant complications in patients receiving breast or chest wall irradiation. We also compared toxic effects and implant complications between patients receiving photon or proton irradiation with prospective near-surface dose optimization.

Materials/methods: Patients at a single institution who received conventionally fractionated breast or chest wall and regional nodal irradiation from 2017-2022 were included. Near-surface rinds (SR3, defined as the volume bound by the breast or chest wall PTV and 3 mm in from the skin) were generated for all patients for analysis. SR3 volumes were used prospectively during proton treatment. SR3 volumes were retrospectively subdivided into axillary SR3, non-axillary SR3, and inframammary SR3 regions. The discrimination performance of near-surface dosimetry for skin and implant toxicity was evaluated using the area under the receiver operating curve (AUC). CTCAE toxicity was compared between patients receiving photon versus proton irradiation using the Pearson's Chi-squared test.

Results: Of 223 patients, 157 and 66 received photon and proton irradiation, respectively. Axillary SR3 D2cc was the strongest dosimetric predictor of moist desquamation (AUC=0.657, p=0.007) and implant failure (AUC=0.880, p=0.017), driven by a stronger predictive ability for moist desquamation in the axillary fold (AUC=0.728, p<0.001). With axillary SR3 D2cc ≤ 48 Gy versus > 48 Gy, rates of moist desquamation were 25.8% versus 48.5% (p<0.001), respectively, and rates of implant failure were 0% versus 20% (p=0.006). Rates of moist desquamation (38.2% versus 27.3%, p=0.12), unplanned reconstructive surgery (35.1% versus 18.8%, p=0.21), and implant failure (8.8% versus 6.3% p>0.99) were similar between patients receiving photon versus proton irradiation.

Conclusions: Near-surface dose predicts moist desquamation and implant failure in patients receiving either photon or proton irradiation of the breast or chest wall. Consideration should be given to limit axillary SR3 D2cc ≤ 48 Gy in appropriately selected patients considered low-risk for skin involvement of cancer.