1060 - Does Pencil Beam Scanning Proton Therapy Impart a Higher Risk of Capsular Contracture when Compared with Intensity Modulated Photon Radiotherapy in the Post-Mastectomy Reconstruction Setting?
Presenter(s)
M. M. Zerey1, O. Gal1, N. Feenstra1, L. Hodgson1, M. A. Fagundes1, M. A. M. Rodrigues1, A. C. Botero1, A. Gutierrez2, A. Wroe1, Z. Fellows1, M. A. Medina1, and J. E. Panoff1; 1Miami Cancer Institute Baptist Health South Florida, Miami, FL, 2Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL
Purpose/Objective(s): Post-mastectomy radiotherapy (PMRT) is associated with increased adverse events in the reconstruction setting. PMRT with proton therapy is increasingly utilized and has been shown to improve cardiac and pulmonary dosimetry. Emerging data indicates that proton therapy is associated with increased risk of capsular contracture (CC) when compared with photon therapy. We compared the CC rate of the largest cohort of pencil beam scanning (PBS) proton PMRT reconstructed patients (pts) to date with an Intensity modulated (IMRT) photon cohort hypothesizing that the proton cohort would have a higher rate of CC.
Materials/Methods: An IRB approved retrospective study was conducted on breast cancer pts who underwent subpectoral two stage tissue expander/implant (TE/I) or direct-to-implant (DTI) breast reconstruction and received either post-mastectomy proton or photon therapy between January 2017 and December 2023 at two centers within a single institution. All TE/I pts had the TE irradiated. CC was defined as offered surgical intervention. Time to CC and 2-year CC rate were assessed using the Kaplan-Meier method. Cox proportional hazards regression analysis, denoted as hazard ratios (HRs) with 95% confidence intervals (CI), was used to assess variables potentially associated with outcome.
Results: The study cohort comprised 175 pts (89 intensity modulated PBS proton; 86 IMRT photon). The median age was 49 years (range 24-78), 63% were Hispanic. Pt demographics including age, race/ethnicity, smoking status, body mass index, menopausal status, molecular subtype, cancer stage, and systemic therapy were well balanced between the groups. Significant differences were observed in tumor laterality (p<0.001) and reconstruction type (TE/I vs. DTI, p<0.001) between the two groups. Median follow up was 42 and 47 months for the proton and photon groups, respectively. Proton pts had higher risk of developing CC compared to the photon group (HR 2.0, 95% CI 1.2-3.2, p<0.01). DTI pts had higher risk of CC compared to TE/I pts (HR 2.8, 95% CI 1.8-4.5, p<0.001). The 2-year CC rate for pts treated with protons and DTI, photons and DTI, protons and TE/I, and photons and TE/I was 61%, 42%, 34%, 21%, respectively (p<0.001). No other pt factors were significantly associated with CC development.
Conclusion: This study adds to the emergent proton PMRT reconstruction literature evaluating the largest and most homogeneous proton PMRT reconstruction cohort to date. DTI pts had higher risk of CC than TE/I. When compared with photon IMRT, proton pts had increased risk of CC. DTI proton pts had the highest risk of CC (69%). Careful consideration of reconstruction technique involving pt input is important in the context of proton PMRT. Assessment of prospective data moving forward will be crucial.