ESTRO 2024 - Abstract Book

S586

Clinical - Breast

ESTRO 2024

1958

Mini-Oral

A phase II trial of hypofractionated adjuvant radiotherapy and simultaneous integrated boost(DEBoRa)

Alessia Di Donato 1 , Edy Ippolito 1,2 , Elisabetta Molfese 1 , Martina Benincasa 1 , Rita Alaimo 1 , Daniela Autieri 1 , Alessia Carnevale 1 , Paolo Matteucci 1 , Antonella Grasso 3 , Paolo Orsaria 3 , Michele Fiore 1,2 , Vittorio Altomare 3,4 , Sara Ramella 1,2 1 Fondazione Policlinico Universitario Campus Bio-Medico, Radiation Oncology, Roma, Italy. 2 Università Campus Biomedico, Radiation Oncology, Roma, Italy. 3 Fondazione Policlinico Universitario Campus Bio-Medico, Breast Unit, Roma, Italy. 4 Università Campus Biomedico, Breast Unit, Roma, Italy

Purpose/Objective:

DEBORA trial was a phase II trial enrolling early stage breast cancer patients <50 years of age with at least one additional risk factor treated with breast conserving therapy and radiotherapy with high dose simultaneous integrated boost (total dose to tumor bed 52.5/3.5 Gy per fraction). Primary endpoint is the 4 year rate of fibrosis. Here we report the interim analysis on the first 50 patients enrolled with regard to acute toxicity. Also late toxicity was reported for patients with at least one year of follow-up.

Material/Methods:

Patients with histologically proven breast cancer who underwent conservative surgery with at least 3 inserted clips on tumor bed and at least one of the following histopathologic additional risk for local recurrence: T >2 cm, N1 disease; unfavourable biology, lymphovascular invasion; close margins (≤4 mm) were considered eligible for the trial. Patients were treated with hypofractionated RT to whole breast to a total dose of 40.05 Gy in 15 fractions (2.67 Gy/die) and a simoultaneous integrated tumor bed dose of 52.5 Gy (3.5 gy/die). VMAT planning was used. Acute Toxicity and Breast fibrosis were evaluated by means of Common Terminology Criteria for Adverse Events (CTCAE) v. 5 scale at baseline and each year during follow-up.

Results:

Between May 2020 and July 2023, 50 consecutive patients, all with an age lower or equal to 50 years old ( median= 48, range= 32-50) were enrolled. Additional risk factor in the patients population were as follows: 13 patients (26.0%) presenting with tumor > 2 cm; 11 (22.0%) patients presenting with N+ disease; 13 patients (26.0%) presenting with unfavourable biology (11, 22% luminal B tumors, 2, 4.0% triple negative tumors). The remaining patients had surgical margin < 4 mm (40.0%). Median follow-up time was 21 months (range: 4-42 months). 36 (72%) patients had a follow-up longer than one year. All the patients completed treatment to the prescribed dose. All patients were evaluable for acute toxicity, 36 (72%) for one year late toxicity. No patients experienced grade >2 acute and subacute toxicity. Table 1 and 2 summarize results on toxicity.

Table 1. Summary of acute and subacute effect (3 months), absolute and relative numbers classified by CTCAE v 5.0