ESTRO 2023 - Abstract Book

S167

Saturday 13 May

ESTRO 2023

In the FAST-Forward trial, acute toxicity outcomes for patients receiving 26 Gy/5-fractions (F) were mild [1]. However, a slightly higher dose of 27 Gy/5F resulted in worse cosmetic and toxicity outcomes up to 5 years after treatment compared to the 26 Gy/5F group [1,2]. As dose distributions in the Netherlands may differ slightly from dose distributions of the FAST Forward trial due to different planning schemes, the aim of this study was to assess clinician-reported acute toxicity in patients with early stage breast cancer treated with 1-week or 3-week adjuvant whole-breast (WBI) or partial-breast (PBI) irradiation without indication for regional nodal irradiation after breast-conserving surgery in the Netherlands. Materials and Methods This study was conducted within the prospective observational UMBRELLA cohort, including patients treated with 26 Gy/5F/1-week or 40 Gy/15F/3-weeks. From October 2021 onwards, the 26 Gy/5F/1-week scheme was clinically implemented as standard of care for selected adjuvant WBI or PBI without indication for regional nodal irradiation after breast-conserving surgery. A subgroup of patients aged ≥ 50 years who were treated with 40 Gy/15F between February 2020 and October 2021, was selected for comparison based on the inclusion criteria for the 26 Gy/5F scheme. Acute toxicity was graded using CTCAE criteria v5.0 before, during and up to four weeks after radiotherapy. Primary endpoint was defined as the proportion of patients with grade ≥ 1 toxicity for breast pain, dermatitis, lymphedema of the breast or fatigue at any time from the start of radiotherapy up to 4 weeks after completion. Results In total, 150 patients were treated with 26 Gy/5F (80% WBI, 20% PBI) and 120 patients with 40 Gy/15F (82.5% WBI, 17.5% PBI). Prior to radiotherapy, breast pain grade 1 was observed in 13% of the 26 Gy/5F patients, dermatitis grade ≥ 1 in 0%, breast edema grade 1 in 5% and fatigue grade ≥ 1 in 15% (Table 1). In the 40 Gy/15F group, 21% experienced breast pain grade ≥ 1, 0% dermatitis grade ≥ 1, 3% breast edema grade 1, and 23% fatigue grade 1. Taking into account the worst CTCAE grade in the 26 Gy/5F group during and up to four weeks after completion of radiotherapy, breast pain grade 1 was experienced by 31% of all patients, dermatitis grade ≥ 1 by 62%, breast edema grade 1 by 17%, and fatigue grade ≥ 1 by 46%. In the 40 Gy/15F group, breast pain grade ≥ 1 was observed in 33% of the patients, dermatitis grade ≥ 1 in 71%, breast edema grade ≥ 1 in 19%, and fatigue grade ≥ 1 in 50%. Conclusion Mild to moderate acute toxicity in the 26 Gy/5F group during and up to four weeks after completion of radiotherapy was comparable to the 40 Gy/15F group. The current results will be complemented with clinician-reported outcomes of 200 patients treated with 26 Gy/5F in Maastro and patient-reported acute toxicity and quality of life up to three months after radiotherapy using the EORTC QLQ-C30/BR23 questionnaires of both UMC Utrecht and Maastro patients.

PD-0232 Skin Dose Predictors of Early-Late Reactions after Whole Breast RT in a Single-Center Large-Cohort A. Cicchetti 1,2 , A. Fodor 3 , P. Mangili 2 , M. Mori 2 , A. Chiara 4 , C. Deantoni 3 , M. Pasetti 3 , G. Palazzo 2 , M.G. Ubeira-Gabellin 5 , T. Rancati 6 , A. Del Vecchio 2 , N.G. Di Muzio 3,3 , C. Fiorino 2 1 Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Prostate Cancer Program, Milan, Italy; 2 San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 3 San Raffaele Scientific Institute, Radiotherapy, Milan, Italy; 4 San Raffaele Scientific Institute, Radiotherapy, milan, Italy; 5 San Raffaele Scientific Institute, Medical, Physics, Italy; 6 Fondazione IRCCS Istituto Nazionale dei Tumori di Miano, Prostate Cancer Program, Milan, Italy Purpose or Objective To assess skin dosimetry predictors of local oedema and hyperpigmentation (EH) in breast cancer patients treated with whole breast moderately hypo-fractionated radiotherapy.