2890 - Accelerated Radiation Therapy (ART) to the Breast and Nodal Stations after Neo-Adjuvant Systemic Therapy and Surgery: A Feasibility Study

Purpose/Objective(s): to evaluate the feasibility of accelerated postoperative radiotherapy in breast cancer patients treated with neoadjuvant chemotherapy and surgery, as measured by the proportion of patients who develop grade II–III dermatitis within 60 days of completing treatment. Secondary Objectives: a) to assess changes in quality of life from baseline to after treatment, b) to determine the incidence of late radiation toxicity such as brachial plexopathy, fibrosis, and telangiectasia, and exploring potential genetic determinants of breast fibrosis. Exploratory Objective: local control, distant recurrence, and overall survival at 2, 5, and 10 years of follow-up, as well as a prospective validation of a molecular signature associated with radiation-induced fibrosis.

Materials/Methods: This prospective phase I–II, non-randomized study evaluated the safety and feasibility of accelerated postoperative radiotherapy delivered in the prone position after neoadjuvant systemic therapy and surgery. Women =18 years with stage I–III breast cancer requiring adjuvant radiotherapy were eligible. Patients were enrolled into two predefined cohorts based on the need for regional nodal irradiation (breast/chest wall alone vs inclusion of level III axillary and supraclavicular nodes). All patients underwent CT simulation in the prone position; supine positioning was used only if normal tissue constraints could not be met. Radiotherapy was delivered to 40.5 Gy in 15 fractions over 3 weeks using 3D-CRT or IMRT. Patients undergoing breast-conserving surgery received a concomitant boost to 48 Gy when indicated. The primary endpoint was grade =2 acute dermatitis within 60 days of treatment completion. Feasibility was defined as limiting grade 3 acute toxicity to <10%. All patients were analyzed on an intent-to-treat basis. Each cohort included 37 patients, providing 80% power (two-sided a=0.05) to detect an increase from a baseline 25% rate of grade =2 dermatitis. If 15 or more patients developed grade =2 dermatitis, the 25% rate would be considered exceeded. Secondary endpoints included prospectively assessed quality of life (BCTOS and SF-36) and late grade =2 toxicity, including fibrosis, telangiectasia, and brachial plexopathy. Exploratory endpoints included local and distant recurrence, recurrence-free survival, and overall survival, estimated using Kaplan–Meier methods.Between 2016 and 2023, 88 patients were enrolled. Five patients withdrew consent before completing protocol therapy. All other patients completed treatment and continue in protocol-defined follow-up. Final analysis is ongoing and will be presented.

Results: TBD

Conclusion: TBD