ESTRO 2025 - Abstract Book

S570

Clinical - Breast

ESTRO 2025

1 Radiation Oncology, University Medical Centre Groningen, University of Groningen, Groningen, Netherlands. 2 Plastic Surgery, University Medical Centre Groningen, University of Groningen, Groningen, Netherlands

Purpose/Objective: Postmastectomy radiotherapy after breast reconstruction for breast cancer (BC) increases reconstruction complication risk. While proton radiotherapy (PrRT) offers advantages in sparing organs at risk, it results in higher skin dose and dermatitis rates [1]. Limited data is available on whether PrRT results in more reconstruction complications compared to photon radiotherapy (PhRT) [2,3]. Our objective is to compare reconstruction complications between hypofractionated PhRT and PrRT. Material/Methods: A retrospective analysis was conducted using prospectively collected data. We included 116 BC patients treated between 2019-2024 with mastectomy and immediate reconstruction, mostly with tissue expander followed by a second surgery for definitive prosthesis after radiotherapy. Of these, 79 patients underwent PhRT and 37 PrRT. The dose regimen consisted of 15 fractions of 2.67 Gy, with 18 patients receiving a thoracic boost. The primary outcome was implant removal after radiotherapy defined as implant replacement or loss. Secondary outcomes included dermatitis and infection after expander-to-implant surgery. Mann-Whitney U and Chi-square tests were used to assess differences between PhRT and PrRT groups and the relationship of the secondary endpoints with implant removal. Binary logistic regression was performed to build an association model for implant removal, evaluating the role of PrRT and confounding by other factors. Factors were included when they modified the regression coefficient of PhRT/PrRT by ≥10%. Results: When evaluating implant removal, no significant differences were observed between PrRT and PhRT groups (table 1). However, the implant loss rate after PrRT was significantly higher than after PhRT (27% versus 6%; p=0.002). There was no significant difference in implant replacement rates between the groups. Patients with infection after expander-to-implant surgery had significantly higher implant removal rates. In the PrRT group, the incidence of grade ≥2 dermatitis was significantly higher than in the PhRT group (70.3% versus 13.9%; p<0.001). No significant difference in implant removal was observed between the dermatitis groups, but there was a significant difference in implant loss.

The association model is shown in table 2. When corrected for the confounding variables, proton therapy has a significant impact on implant removal. Bolus also results in a significantly higher implant removal, suggesting that higher skin-dose plays a role.