ESTRO 2024 - Abstract Book

S610

Clinical - Breast

ESTRO 2024

2088

Digital Poster

Fat necrosis after One-week Partial Breast Irradidation VS Standard of Care: a case-control study.

Riccardo Ray Colciago 1 , Eliana La Rocca 2 , Carlotta Giandini 1 , Giulia Bianchi 3 , Ilaria Maugeri 4 , Catherine Depretto 5 , Silvia Meroni 6 , Anna Cavallo 6 , Emanuele Pignoli 6 , Laura Lozza 1 , Tiziana Rancati 7 , Maria Carmen De Santis 1 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Department of Radiation Oncology, Milan, Italy. 2 Azienda Ospedaliero Universitaria Integrata, Department of Radiation Oncology, Verona, Italy. 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Oncology Department,, Milan, Italy. 4 Fondazione IRCCS Istituto Nazionale dei Tumori, Breast Unit, Milan, Italy. 5 Fondazione IRCCS Istituto Nazionale dei Tumori, Breast Imaging Unit, Radiology Department, Milan, Italy. 6 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics Unit, Milan, Italy. 7 Fondazione IRCCS Istituto Nazionale dei Tumori, Data Science Unit, Milan, Italy

Purpose/Objective:

One-week external beam partial breast irradiation (PBI) showed high fat necrosis rates shown in the literature [1]. This study aimed to compare the incidence of fat necrosis after PBI vs hypofractionated whole breast irradiation (WBI) in patients with early-stage breast cancer.

Material/Methods:

From our institutional registry, we selected 975 early-stage BC patients who underwent breast conservative surgery and adjuvant radiotherapy between 2009 and 2022. Radiation therapy consisted of Partial Breast Irradiation of 30 Gy in 5 daily fractions (delivered in one week, consecutively) to the tumor bed, delivered with Volumetric Modulated Arc Therapy (VMAT) technique (Group A) or WBI (42.4Gy in 16 fractions) (Group B) delivered with 3D conformal radiotherapy. Tumor bed boost and chemotherapy were exclusion criteria.

We matched, with a case-control approach, patients by age, pathological tumor stage (T-stage) and diabetes diagnosis.

Data on fat necrosis were retrospectively retrieved from yearly mammograms and breast ultrasound reports.

Primary endpoint was the incidence of radiologically detected fat necrosis. We used a chi-squared test to assess the association of crude rates of fat necrosis with irradiation technique. We also performed a univariate Cox proportional-hazards regression analysis to assess the association between irradiation technique and actuarial fat necrosis rates.

Results:

From the case-control match, Group A and Group B consisted of 88 pts each, treated with PBI and WBI, respectively.