Novel accelerated partial breast irradiation simultaneous integrated boost technique: Rush experience.

Abstract

e12536 Background: Breast cancer is the most common malignancy among U.S. women. Radiation therapy after lumpectomy reduces recurrence but requires multiple sessions, creating barriers related to time, access, and cost. Newer approaches of shorter fractionation schedules aim to maintain efficacy while minimizing treatment burden and side effects. Accelerated partial breast irradiation (APBI) with simultaneous integrated boost (SIB) delivers higher doses to the tumor bed in fewer treatments, improving convenience without compromising local control. However, guidelines of the American Society for Radiation Oncology (ASTRO) are limited by underrepresentation of patients with higher-risk clinical or pathologic features in major trials. Real-world data are needed to better define APBI candidacy for these groups. Methods: This retrospective cohort study evaluates patients treated with 5-fraction APBI with SIB at Rush University Medical Center between March 2023 and July 2025. Eligible patients are aged ≥18 years with stage I–II invasive ductal carcinoma (IDC) or ductal carcinoma in situ (DCIS) who underwent breast-conserving surgery followed by a 5-fraction regimen. Exclusions are metastatic disease at diagnosis, or incomplete records. Patients are grouped per ASTRO APBI categories (“recommended,” “conditionally recommended,” and “conditionally not recommended”). Collected variables include tumor features, surgical details, systemic therapy, radiation parameters, and acute toxicity. Results: Current evidence shows APBI provides comparable toxicity across diverse patient subgroups while reducing overall treatment time and maintaining local control. SIB delivery appears feasible and safe, with potential benefit for patients with higher-risk features. As of December 2025, our cohort includes 87 patients with a median follow-up of 327 days. Of these, 54 patients had IDC and 33 had DCIS. According to ASTRO criteria, 54 patients were “recommended,” 31 “conditionally recommended,” and 2 “conditionally not recommended.” Two local recurrences occurred, both in the “recommended” category. No significant differences in acute toxicities were observed among risk groups, though longer follow-up is needed. Conclusions: This study provides real-world evidence on outcomes of 5-fraction APBI with SIB, particularly among patients historically underrepresented in clinical trials. Findings will help refine selection criteria, clarify safety in higher-risk groups, and support more individualized and accessible radiation therapy strategies for early-stage breast cancer.