ESTRO 2025 - Abstract Book

S510

Clinical - Breast

ESTRO 2025

CTCAE version 4.03 were assessed weekly during treatment and then 2-3 weeks, 6 weeks and 12 weeks post treatment.

Results: Twenty-four patients were accrued with 6 treated in each DL. The majority of patients had cT1/2 tumours (n = 23), 1 had a cT3 tumour, 4 had nodal involvement (N1 = 4) and 3 patients had M1 disease. The acute toxicity stopping rule was not met at any DL. No patient experienced grade 3 toxicity in any domain and no patients experienced grade 2 desquamation. Five patients experienced grade 1 (dry) desquamation within 12 weeks of treatment (36 Gy, n = 1; 40 Gy, n = 1; 48 Gy, n = 3). One patient (36Gy DL) experienced grade 2 erythema. There were no patients with grade 2 toxicity in any of the other domains. Conclusion: This dose escalation study using SABR as primary therapy for intact breast cancers showed very low acute toxicity despite delivering ablative doses (up to BED = 105Gy 10 ). Based on the toxicity reported here and assuming that dose-escalation provides better local control, this study suggests that the highest DL used, 48Gy in 4 fractions, is a suitable option for future clinical trials exploring primary radiotherapy for breast cancer. Long term outcomes, including QoL questionnaires and VAS pain scale will be reported once the data is mature, which will be essential to confirm these preliminary safety results. Digital Poster Continuous positive airway pressure for heart subvolumes sparing in left-sided breast cancer radiotherapy: A novel efficient alternative to DIBH? Zeineb Naimi 1 , Amal Riahi 1 , Azza Slim 2 , Raouia Ben Amor 1 , Awatef Hamdoun 1 , Ghada Bouguerra 1 , Rihab Haddad 1 , Lotfi Kochbati 1 1 Radiation Oncology Department, Abderrahmen Mami Hospital, Ariana, Tunisia. 2 Pneumology Department, Abderrahmen Mami Hospital, Ariana, Tunisia Purpose/Objective: This study aimed to assess the dosimetric impact of using continuous positive airway pressure (CPAP) in left sided breast cancer radiotherapy in terms of lung and heart substructures sparing. Material/Methods: Patients with left-sided breast cancer referred for adjuvant radiotherapy, between January and April 2024, were prospectively enrolled in this study. Patients were trained to breath with CPAP device using a facial mask, for 30 minutes under a maximum tolerable pressure ranging between 10 and 15 cmH2O. For each patient, two simulation CTs were performed: with free breathing (FB) and with CPAP. Treatment plans were generated for both simulation CTs using a 3D conformal technique, aiming at respecting target volume coverage objectives and OAR doses constraints. The prescription dose was 40.05Gy/15 fractions +/- an additional boost of 10 Gy to the tumor bed. Dose volume histograms for the ipsilateral lung, heart, left ventricle (LV) and left anterior descending artery (LAD) were statistically compared between both plans, using the t student test. Keywords: SABR, Clinical Trial, dose escalation 2130