2669 - Photon vs. Proton Post-Mastectomy Radiotherapy Toxicities in Pre-Pectoral Implant-Based Breast Reconstruction

S. Choi¹, D. A. Cerbon¹, A. Desai², C. Padilla³, S. Han⁴, I. M. Reis⁵, J. R. Mella-Catinchi⁶, D. P. Singh⁶, and C. Takita¹; ¹Department of Radiation Oncology, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, ²DeWitt Daughtry Family Department of Surgery, University of Miami/Sylvester Cancer Center, Miami, FL, ³Universidad del Norte, Barranquilla, Colombia, ⁴Biostatistics and Bioinformatics Shared Resources, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, ⁵Department of Public Health Sciences and Sylvester Biostatistics/Bioinformatics Shared Resources (BBSR), University of Miami, Sylvester Comprehensive Cancer Center, Miami, FL, ⁶DeWitt Daughtry Family Department of Surgery, Division of Plastic and Reconstructive Surgery, University of Miami, Miami, FL

Purpose/Objective(s): We aimed to compare radiation toxicities and reconstructive complications after photon and proton post-mastectomy radiotherapy (PMRT) among patients who received pre-pectoral implant-based breast reconstruction (PP-IBBR). The hypothesis is that proton PMRT will yield fewer radiation toxicities and reconstructive complications. Materials/

Methods: A single-institution retrospective cohort study included breast cancer patients undergoing mastectomy and PP-IBBR followed by PMRT (Jan 2020-Oct 2022) with one-year follow-up. Acute radiation toxicities of interest were dermatitis, esophagitis, and fatigue. Reconstructive complications included minor infection (requiring oral antibiotics), major infection (intravenous antibiotics with hospital admission), wound, implant exposure, flap necrosis, seromas, re-operations, capsular contracture, and implant failures. The rates of toxicities and complications between proton and photon PMRT were compared using Chi-square test or Fisher’s exact test. Group comparison of continuous variables was assessed using Wilcoxon rank-sum test. Logistic regression analyses identified clinical factors associated with =2 surgical complications.
Results: 114 patients met inclusion criteria. Two patients had bilateral implants/radiation, therefore 116 PP-IBBR receiving PMRT (75 photon and 41 proton). There was a significant difference between photon (n=66) and proton (n=40) groups regarding prescription mean PMRT dose (median 42.56 Gy vs 50 Gy, p<.0001), and fractionation was conventional (45-50.4 Gy/25-28 Fractions) in 17 photon patients (25.8%) vs 40 (100%) photon vs proton groups, respectively. There was no significant differences between the two groups with respect to radiation toxicities: dermatitis grade 1 (78.7% in photon vs 78% in proton), grade 2 (14.7% vs 19.5%), and grade 3 (1.3% vs 0%); esophagitis grade 1 (32% vs 24.4%), grade 2 (10.7% vs. 4.9%); and fatigue (26.7% vs 29.3%). For surgical complications, 7.8% (n=9) implants had major infections (Photon 9.3% vs Proton 4.9%) and 0.9% (n=1) had minor infections (Photon 1.3% only). 7.8% (n=9) had wound complications (Photon 10.7% vs Proton 2.4%); 0.9% (n=1) had partial flap necrosis (Photon 1.3% only); 2.6% (n=3) had seromas (Photon 4% only); 15.5% (n=18) had re-operations for any surgical complications (Photon 20% vs Proton 7.3%); 14.7% (n=17) had implant failure (Photon 18.7% vs Proton 7.3%); 18.1% (n=21) had grade 3 or 4 capsular contracture (Photon 18.7% vs Proton 17.1%). Photon was significantly associated with a higher risk of =2 surgical complications in univariable analysis (OR: 3.71, 95% CI: 1.02-13.53, p=0.047) and in the multivariable model adjusting for stage (OR: 4.84, 95% CI: 1.27-18.46, p=0.021).
Conclusion: Compared to traditional photon PMRT, proton PMRT had fewer surgical complications but no difference regarding radiation toxicities in patients with PP-IBBR.