241 - Comparison of Acute and Late Toxicities with Daily vs. Every Other Day Five Fraction Partial Breast Radiation Therapy

S. M. Parker¹, A. Halima², E. E. Obi², C. Billena², Z. Al-Hilli³, S. Cherian², R. D. Tendulkar², and C. S. Shah²; ¹Department of Radiation Oncology, Cleveland Clinic, Cleveland, OH, ²Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, ³Breast Center, Integrated Surgical Institute, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): Partial breast irradiation (PBI) delivered with intensity modulated radiation therapy (IMRT) over 5 fractions every other day (QOD) represents an attractive and convenient method of delivering adjuvant radiation therapy for well selected patients without compromising oncologic or aesthetic outcomes. Condensing this regimen to a week of treatment through daily delivery of PBI may further increase patient convenience. In this investigation we report our institutional experience of daily versus QOD 5 fraction PBI. Materials/

Methods: We retrospectively reviewed 507 patients from an institutional registry undergoing PBI for DCIS or early-stage breast cancer (T1-2N0/x) from 2015 to 2022. All patients received 30 Gy in 5 fractions delivered with IMRT. Both acute (toxicity within 90 days of treatment) and late toxicity were recorded. Toxicity evaluated included fatigue, dermatitis, telangiectasia, hyperpigmentation, fibrosis/induration, and lymphedema. Univariate analysis was performed using Mann-Whitney U-tests and chi-squared tests. Kaplan-Meier analysis was used to compare local control.
Results: Of the 507 patients, 351 were treated with QOD and 156 were treated daily. Median follow up was longer in the QOD group (2.4 vs 1.9 years). Stage was well balanced: Tis (10% QOD, 9% daily), T1 (86% QOD, 89% daily), and T2 (3% QOD, 4% daily). Most patients were ER positive (98% QOD, 99% daily) and underwent adjuvant endocrine therapy (85% QOD, 86% daily). Patients were well balanced between both groups with no significant differences in median age (67 QOD vs 67 daily), baseline comorbidities (diabetes, CAD, obesity, asthma, hypertension, hyperlipidemia), and smoking status. Rates of grade 1 (39% QOD vs 33% daily) and grade 2 (0% QOD vs 1% daily) acute dermatitis were not different between groups (p=0.06). Rates of grade 1 (18% QOD vs 24% daily) and grade 2 (1% QOD vs 1% daily) acute fatigue were similar as well (p=0.09). Late hyperpigmentation (14% QOD vs 14% daily, p=0.97), telangiectasia (1% QOD vs 1% daily, p=0.92), mild fibrosis/induration (13% QOD vs 13% daily, p=0.91), lymphedema (0% QOD vs. 1% daily, p=0.31), and unspecified mild radiation changes (5% QOD vs 5% daily, p=0.89) were not significantly different. Late toxicity rarely required additional surgical intervention for painful fibrosis or contracture (1% QOD vs 1% daily, p=0.92). Local control at 2 years was similar between groups (99.6% QOD vs 100% daily, p=0.51).
Conclusion: Overall, 5 fraction partial breast irradiation delivered daily appears to be well tolerated with similar acute and late toxicity to every other day fractionation.