S270
Clinical - Breast
ESTRO 2026
Centro Bio-RT, Brescia, Italy. 6 Medical Physics, Centro Bio-RT, Brescia, Italy
developed grade 2 radiation-induced pneumonitis. 45 patients have a follow-up of 1 year or more. In that group, we still observed hyperpigmentation in 40% and breast pain in 20% of the cases, with 0.4% requiring analgesics. Fibrosis, mainly grade 1, was noticed in 37.8%. Other side-effects include telangiectasia in 6.7%, breast edema in 0.4% and breast shrinkage in 0.7%. Physician-reported cosmetic outcomes were excellent or good in 97.9% of cases. No recurrences were observed. Conclusion: Ultra-hypofractionated WBI in 5 daily fractions with an SIB to the tumor bed appears feasible and well- tolerated. We observed low rates of acute adverse events and excellent cosmetic results. Further studies and longer follow-up are required to assess late toxicity profile, as well as oncological outcomes. References: EBCTC Group, "Effect of radiotherapy after breast- conserving surgery on 10-year recurrence and 15-year breast cancer death" Lancet 2011Murray Brunt et al. "Hypofractionated breast radiotherapy for 1 week versus 3 weeks (FAST-Forward)" The Lancet 2020Collette et al. “Predictors of the risk of fibrosis at 10 years after breast conserving therapy for early breast cancer” European Journal of Cancer 2008Vicini et al. “NRG RTOG 1005: A Phase III Trial of Hypo Fractionated Whole Breast Irradiation with Concurrent Boost vs. Conventional Whole Breast Irradiation” IJROBP 2022Montero et al. “Acute skin toxicity of ultra- hypofractionated whole breast radiotherapy with SIB for early breast cancer” Clinical and Translational Radiation Oncology 2023 Keywords: hypofractionation, simultaneous integrated boost Adaptive Accelerated Partial Breast Irradiation with a 1.5 T MR-linac using daily Adapt-to-shape workflow and Comprehensive Motion Management. Andrea E Guerini 1,2 , Lanfranco Chirico 1,3 , Sara Pedretti 1 , Mirsada Katica 2 , Stefania Nici 4 , Ludovica Pegurri 1 , Stefano Riga 4 , Giorgio Facheris 1 , Gianluca Cossali 1 , Marta Maddalo 1 , Loredana Costa 1 , Eneida Mataj 2 , Martina C Daniotti 4 , Martina Peretti 4 , Paolo Borghetti 1 , Marco L Bonù 1 , Luca Triggiani 2 , Cristian Toraci 4 , Stefano M Magrini 2,5 , Luigi Spiazzi 4,6 , Michela Buglione di Monale 2,5 1 Radiation Oncology, ASST Spedali Civili, Brescia, Italy. 2 Radiation Oncology, Università degli Studi di Brescia, Brescia, Italy. 3 Radiation Oncology, Università degli Studi di Milano, Milano, Italy. 4 Medical Physics, ASST Spedali Civili, Brescia, Italy. 5 Radiation Oncology, Digital Poster 2241
Purpose/Objective: reduction of treatment volumes and number of fractions in APBI increase the impact of inter and intra- fraction anatomical variations on optimal dose delivery. MRI-guided radiotherapy (MrgRT) using the Elekta Unity 1.5 T MR-linac,enables better soft-tissue visualization and adaptive planning. The new Comprehensive Motion Management (CMM) system also allows for intra-fraction motion control. In this preliminary analysis, we assessed the clinical feasibility and toxicity profile of a full adaptive MrgRT
workflow for APBI. Material/Methods:
we prospectively analyzed data of patients treated with APBI from May 2025 to October 2025 using Unity system. All patients were treated according to "Florence" APBI protocol (30 Gy in 5 fractions) using an adapt-to-shape (ATS) workflow, in which the T2- weighted MRI acquired on-board is deformably registered with the reference MRI, target and OARs contours are edited on the basis of the anatomy of the day and treatment plan re-optimized.During delivery, CMM continuously monitored the target with cine-MRI, with beam gating in case of displacement > 5mm; mean and 95th percentile PTV displacements were calculated in x (latero-lateral), y (cranio-caudal) and z (antero-posterior) axes. Duty-cycle was calculated as beam-on time/total delivery time. Toxicities were graded according to CTCAE v5.0 criteria. Results: data from 14 consecutive patients were analyzed. All underwent conservative surgery and had pT1-2 R0 pN0, grade 1-2, cerb-B2 negative non-special type breast carcinoma, with 91-100% ER expression and ki67<30% (mean expression 14%). Disease side was right for 64% patients and left for 36%. All the fractions were delivered within 40 minutes. PTV coverage was adequate and dosimetric costraints for the main OARs were consistently respected in all the fractions, with only minor violations of controlateral breast dose. Acute toxicity was mild and equivalent to previous series of patients treated with conventional linacs, with only G1 completely reversible events in 57% of patients (as described in Table 1).
No radiation-indiced toxicity was reported 3 months
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