2716 - Safety and Efficacy of Hypofractionated Radiation Therapy in Patients who undergo Post mastectomy Radiation Therapy

O. E. Ojo^1,2, B. Gui^1,2, L. Ottensoser^1,2, K. Ajay³, C. Evans^2,4, L. Tchelebi^1,2, L. Lee^2,5, and G. Wernicke^2,6; ¹Department of Radiation Medicine, Northwell, Lake Success, NY, ²Northwell, Lake Success, NY, ³Northwell, New Hyde Park, NY, ⁴Department of Radiation Medicine, Northwell, New Hyde Park, NY, ⁵Northwell, Department of Radiation Medicine, Lake Success, NY, ⁶Department of Radiation Medicine, Northwell, New York, NY

Purpose/Objective(s): Post-mastectomy radiation therapy (PMRT) is integral in managing breast cancer patients. Several studies have validated the use of hypofractionation in the management of patients following breast conserving surgery, but less data to support hypofractionation are available for patients requiring adjuvant PMRT. In this retrospective study, we evaluated outcomes, toxicity, and cosmetic results in patients treated with hypofractionated PMRT (hfPMRT) at our center. Materials/

Methods: After obtaining IRB approval, we reviewed the patients who underwent mastectomy +/- reconstruction and were treated with adjuvant hfPMRT between 2016-2024. Reconstruction types were recorded. Ipsilateral chest wall recurrence (ICWR) and regional nodal recurrence (NR), overall survival (OS), disease-free survival (DFS) as well as complications and toxicity, and cosmetic outcomes were analyzed. T-test, Chi-square test and Kaplan-Meier analysis were performed, using data management and decision management software.
Results: A total of 58 patients were treated with PMRT to 4240 -5250 cGy in 16-20 fractions to the chest wall and comprehensive regional nodes. Median age 62 years (38 – 90 years). 29 (50%) patients had neoadjuvant chemo and 39 (67%) adjuvant chemo or endocrine therapy. 25 (43%) patients had axillary dissection. Of 26/56 (46%) patients who had reconstruction: 13 (50%) had immediate DIEP reconstruction and 13 (50%) had pre-RT expansion with an expander who went on to get post-RT exchange for a permanent implant, and 2 had post-RT DIEP. With median follow up of 24 months (1 - 96 months), there were 2 ICWR (3%), 2 ipsilateral axillary NR (3%), and 5 distant metastases (9%). The 2-year OS and DFS were 93%and 82%, respectively. Grade 2 acute skin toxicity, Grade 2 late skin toxicity, brachial plexopathy, lymphedema rate cosmesis (shrinkage/induration) were 14%, 2%, 0%, 12%, and 7%, respectively. There were no differences in acute or late toxicities, lymphedema, cosmesis in patients with reconstruction vs. without reconstruction (p=0.45, 0.50, 0.45, 0.31). Among patients with reconstruction, there was no difference in acute, late toxicities, cosmesis or lymphedema for immediate DIEP vs. upfront expander (p=0.48, 0.60, 1.00, 0.04). There were more Grade 2 acute skin toxicity (24% vs. 6%, p=0.049) ALND compared to SLNB.
Conclusion: Adjuvant hfPMRT resulted in low rates of recurrence, toxicity and acceptable cosmetic results. hfPMRT may therefore provide a convenient, safe and effective option. Prospective data is awaited to validate these results.