ESTRO 2025 - Abstract Book

S478

Clinical - Breast

ESTRO 2025

1304

Digital Poster Combined IOERT boost and moderate hypofractionated vs conventional Whole-Breast Irradiation: a long term safety and cosmetic outcome analysis Grazia Lazzari 1 , Antonietta Montagna 1 , Barbara D'Andrea 1 , Ilaria Benevento 1 , Vito Metallo 1 , Giovanni Castaldo 1 , Luciana Rago 1 , Raffaele Tucciariello 2 , Antonella Bianculli 2 1 Radiation Oncology Unit, IRCCS-CROB, Rionero in Vulture, Italy. 2 Physic Unit, IRCCS-CROB, Rionero in Vulture, Italy Purpose/Objective: To evaluate retrospectively a long term safety and cosmetic outcome of intraoperative electron boost (IOERT) with hypofractionated (H-WBI) vs conventional (C-WBI) whole breast irradiation in early breast (BC) patients in our experience. Material/Methods: Patients (pts) with pT1-2 N0-1 BC received 10 Gy-12 Gy IOERT boost (90% reference dose) during conservative surgery followed by 3D/IMRT-WBI. Several schedules of moderately hypofractionated or conventional radiotherapy (RT) were applied with 3D or IMRT techniques . Late toxicity according to the common toxicity criteria for skin adverse effects (CTCAE 5.0) on the tumor bed and the overall cosmetic results by the Harvard scale were analyzed. Cox proportional hazards regression was used to define the cumulative incidence of late toxicity and cosmetic outcome among the hypofractionated schedules and conventional RT WBI. Pearson’s covariance for multivariate analysis was appplied to assess significant prognosticators for late toxicity according fractionation (p <0.005). Results: Between 2012 and 2021 90 consecutive pts received 10 Gy-12 Gy IOERT boost during conservative surgery followed by 3D /IMRT-WBI. Mean age was 57 year (40-70 yrs). After 28-day mean interval (25-30), WBI was delivered. Moderately hypofractionated RT as 2.67 Gy/15/ 40.05 Gy in 25 pts , 2.66 Gy/ 16/ 42.5 Gy, and 3.2 Gy/13/41.6 was allowed to 45 pts; conventional RT 2 Gy/25/50 Gy was delivered to 45 pts.WBRT with 3D or IMRT was delivered in both group. Median follow-up was 9.8 years. The ten year cumulative incidence of G2-G3 late toxicity (pain, fibrosis, skin oedema, telangectasia, ulceration and fat necrosis) in the tumor bed was 22%-13% in the C-WBI and 33%-22% (in the H-WBI (p= 0.023; p= 0.038 respectively ). Cosmesis scored as excellent/good was in 80 % for H-WBI and 87 % for C-WBI (p= 0.67). At multivariate analysis in the H-WBI group hot spot > 105% of the PD in the boost area (p= 0.03), irradiated breast volume < 1000 cc ( p= 0.024), collimator size > 4 cm (p=0.045), dose 12 Gy ( p= 0.002), electron energy > 8 MeV(p= 0.034) , fraction size > 3 Gy ( p= 0.001) , 3D technique ( p= 0.0021) were significant prognosticators for late toxicity.

Conclusion: IORT boost and moderately H-WBI achieved a long term acceptable late toxicity in the tumor bed and no differences in cosmetic outcome. However patient selection and dosimetric analysis are mandatory in IOERT boost with H-WBI.

Keywords: boost, IOERT, toxicity