ESTRO 2023 - Abstract Book

S1019

Digital Posters

ESTRO 2023

PO-1275 Ultra-hypofractionated breast radiotherapy & simultaneous integrated boost for early breast cancer

A. Montero 1 , C. Cañadillas 1 , R. Ciervide 1 , M. Garcia-Aranda 1 , B. Alvarez 1 , A. Prado 2 , X. Chen-Zhao 1 , J. Valero 1 , M. Lopez 1 , R. Alonso 1 , O. Hernando 1 , E. Sanchez 3 , J. Garcia 2 , K. Rossi 1 , M. Izquierdo 1 , P. Fernandez-Leton 2 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Medical Physics, Madrid, Spain; 3 HM Hospitales , Radiation Oncology, Madrid, Spain Purpose or Objective Whole-breast irradiation (WBI) after breast conserving surgery (BCS) is indicated to improve loco-regional control and survival. Former studies showed that addition of tumor bed boost in all age groups significantly improved local control with no apparent impact on overall survival but with an increased risk of worse cosmetic outcome. Shortened regimens in 3 weeks are considered the standard but recent studies have shown the non-inferiority of 5 fractions in one-week in both locoregional control and toxicity profile. We present our preliminary results of tolerance of ultra hypofractionated (UHF) in one week WBI schedule with simultaneous integrated boost (SIB) in early breast cancer. Materials and Methods From March-2020 to March-2022, 383 patients with a median age of 56 years (range 30-99) were treated according to our institution UHF radiotherapy schedule after BCS. Clinical staging (AJCC): Tis 77p (20%), T1a 26p (7%), T1b 87p (22%), T1c 163p (43%), T2 29p (8%). All patients were pN0 Radiotherapy comprises WBI at 26Gy@5.2Gy/day with a SIB to all patients up to a total dose of 29Gy@5.8Gy/day in 272p (71%), 30Gy@6Gy/day in 100p (26%) and 31Gy@6.2Gy/day in 11p (3%) depending upon margin status. WBI+SIB was delivered by conformal 3-D technique in 366p (96%), VMAT in 16p (4%). Four patients (1%) underwent radiation treatment with deep inspiration breath hold (DIBH). Treatment beam arrangement for SIB comprised of coplanar 2 beams in 2p (0.5%), 3 beams in 142p (37%), 4 beams in 194p (51%), 5 beams in 25p (7%), 9 beams in 1p (0.2%) and 2 arcs in 11p (3%). Median PTV breast volume (mPTVbreast) 725cm3 (114-2409cm3); median PTV boost volume (mPTVboost) 28 cm3 (4.6-198cm3). Dose constraints are detailed in table 1 Systemic therapy: 355p (93%) received hormone therapy and 43p (11%) systemic or targeted chemotherapy. Acute and late toxicities were evaluated according to RTOG/EORTC criteria. Pearson’s Chi square test was used to compare characteristics among different subgroups and statistical significance was considered when reaching a p value <0.05.