Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
2906 - Risk Factors for High-Grade Dermatitis Following Breast/Chest Wall and Regional Nodal Irradiation with Proton Beam Radiotherapy: Results of a Multi-Institutional Prospective Registry Trial
Presenter(s)
Dulcce Valenzuela, MS, BS - Inova Schar Cancer Institute, Fairfax, VA
D. Valenzuela1, A. A. Bhatti1, A. D. Rao1,2, A. K. Chawla1,2, L. Majithia Jr1,2, S. Hetelekidis1,2, S. Gao1,2, E. S. Kowalski1,2, K. E. Marqueen1,2, G. K. Bajaj1,2, E. M. Nichols3, C. B. Simone II4, and I. J. Choi4; 1Inova Schar Cancer Institute, Falls Church, VA, 2Radiation Oncology Associates of the National Capital Region, Falls Church, VA, 3Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 4New York Proton Center, New York, NY
Purpose/Objective(s):
High-grade dermatitis (HGD; RTOG =2) is a clinically meaningful toxicity during breast/chest wall radiotherapy. This study evaluated whether surgery type (breast-conserving surgery [BCS] vs mastectomy), proton technique (PBT; pencil beam scanning [PBS] vs uniform/double scattering [US/DS]), and dose per fraction (D/Fx; 1.8 vs 2.0 Gy) were associated with acute HGD in women treated with conventionally fractionated adjuvant proton therapy on a multi-institutional registry trial.Materials/Methods:
Women receiving adjuvant proton radiotherapy to the breast/chest wall and regional nodes were identified; exclusions included metastatic/palliative intent, partial breast, absence of nodal data, and non-standard fractionation. The cohort included 287 patients (median age 54 years), treated from 2013-2025. Covariates include age, surgery type, PBT, reconstruction, concurrent chemotherapy, D/Fx, total dose, and fraction number. HGD was analyzed as a binary endpoint. Univariate odds ratios (ORs) used Fisher’s exact or ?² tests. Bayesian logistic regression addressed small US/DS numbers and correlated predictors. Primary model evaluated mastectomy vs BCS adjusted for PBT, age, and D/Fx; a mastectomy-only model evaluated reconstruction. Posterior adjusted ORs (aORs), 95% credible intervals (CrIs), and P[OR>1] were estimated.Results:
HGD occurred in 183/287 (63.8%). Crude HGD rates were similar after mastectomy vs BCS (65.2% vs 62.6%; OR 1.12, p=0.79). US/DS showed higher crude HGD than PBS (77.8% vs 62.3%; OR 2.11, p=0.09). Reconstruction after mastectomy was associated with higher HGD (77.4% vs 58.6%; OR 2.42, 95% CI 0.90–6.52, p=0.10). Concurrent chemotherapy showed no increase in HGD (58.3% vs 64.3%; OR 0.78, p=0.66).
In the primary Bayesian model, mastectomy was not independently associated with HGD (aOR 1.05, 95% CrI 0.59–1.82, P[OR>1] = 0.56). US/DS showed a directional but imprecise increase (aOR 1.54, 95% CrI 0.66–3.93, P[OR>1] = 0.84). Higher D/Fx showed a modest protective trend (aOR 0.78, 95% CrI 0.60–1.02, P[OR>1] = 0.04). In mastectomy-only modeling, reconstruction was associated with substantially higher HGD risk (aOR 3.01, 95% CrI 1.12–9.41, P[OR>1] = 0.99).
Conclusion:
After adjusting for PBT, age, and D/Fx, mastectomy was not independently associated with HGD. US/DS showed a consistent but uncertain trend in HGD relative to PBS, whereas 2.0 Gy per fraction showed a modest protective trend. Reconstruction after mastectomy was associated with substantially higher HGD risk. Overall, PBT and reconstructive status—not surgery type—better stratify dermatitis risk, supporting PBS-based skin-sparing strategies and enhanced prophylaxis for reconstructed mastectomy breast cancer patients.