ESTRO 2025 - Abstract Book

S558

Clinical - Breast

ESTRO 2025

3047

Digital Poster Early data from PRISCILLA prospective trial: partial breast irradiation for low and intermediated grade ductal carcinoma in situ (NCT05663294) Ruggero Spoto 1 , Antonio Marco Marzo 1 , Icro Meattini 2,3 , Agnese Prisco 4 , Maria Carmen De Santis 5 , Matteo Augugliaro 6 , Maria Cristina Leonardi 7 , Luca Visani 8 , Luca Dominici 1 , Isabella Palumbo 9 , Davide Franceschini 1 , Alfio Di Grazia 10 , Anna Bertolini 11,12 , Luca Nicosia 13 , Barbara Campanella 14 , Alessandro Parisi 15 , Andrea Girlando 16 , Marco Trovò 4 , Cyhthia Aristei 9 , Lorenzo Livi 2 , Marta Scorsetti 1,11 1 Radiotherapy and Radiosurgery Department, IRCCS Humanitas Research Hospital, Rozzano, Italy. 2 Department of Experimental and Clinical Biomedical Sciences “M. Serio”, University of Florence, Florence, Italy. 3 Radiation Oncology, Breast Unit, Azienda Ospedaliero-Universitaria Careggi,, Florence, Italy. 4 Department of Radiation Oncology, University Hospital of Udine, ASUFC, Udine, Italy. 5 Radiation Oncology, Fondazione IRCCS Istituto Nazionale Tumori di Milano, Milano, Italy. 6 Radiotherapy Unit, Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, Italy. 7 Department of Radiotherapy, European Institute of Oncology IRCCS, Milan, Italy. 8 Radiation Oncology, Azienda Ospedaliero Universitaria Careggi, Florence, Italy. 9 Radiation Oncology Section, Department of Medicine and Surgery, University of Perugia and Perugia General Hospital, Perugia, Italy. 10 Radioterapia Humanitas, Humanitas Istituto Clinico Catanese, Catania, Italy. 11 Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Italy. 12 Department of Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Rozzano, Italy. 13 Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria Hospital, Negrar di Valpolicella, Italy. 14 Department of Medicine and Surgery and Translational Medicine, Sapienza University of Rome, Rome, Italy. 15 Radiotherapy Unit, Istituto Oncologico Veneto - IRCCS, Padova, Italy. 16 Department of Radiation Oncology, Humanitas Istituto Clinico Catanese, Catania, Italy Purpose/Objective: Postoperative radiation therapy effectively reduces recurrence risk in ductal carcinoma in situ (DCIS) 1 . To investigate potential treatmentoptimisation for low- and intermediate-risk DCIS, accelerated partial breast irradiation (APBI) warrants evaluation 2-4 . This phase II prospective multicentre trial assesses the efficacy of APBI, reporting early results on acute toxicity. Material/Methods: Patients with pathologically confirmed DCIS were recruited from 11 centres across Italy. Inclusion criteria were low risk DCIS (nuclear grade 1–2, lesions ≤3 cm, resection margins ≥2 mm) and intermediate-risk DCIS (nuclear grade 3, lesions ≤1 cm, resection margins ≥2 mm). Following quadrantectomy, APBI targeted the surgical bed. Patients were assessed at treatment completion and at 1- and 3-month post-treatment. Toxicity was graded using CTCAE v5.0 scale. Results: Between January 2023 and June 2024, 150 patients were enrolled. All underwent quadrantectomy, with APBI delivered within 4 months post-surgery. DCIS histological grades at surgery were: G1 (21 patients), G2 (102 patients), G3 (23 patients), and unknown grade (4 patients). The median tumourdiameter was 0.8 cm (SD ±1.09 cm). Surgical bed clips for localization were present in 66% of cases. Radiation therapy schedule was 30Gy in 5 fractions to all but one patient. The median V95% PTV coverage was 97.5% (SD ±2.1%), and the mean heart dose was 0.8Gy (SD ±0.5Gy). Acute toxicity data were available for 130 patients. No grade 3 or 4 toxicities were observed. Most toxicities were grade 1, with a single case of grade 2 radiation dermatitis reported (Table 1). At treatment completion, radiation dermatitis occurred in 26.9% of patients, followed by breast oedema (9.6%). Acute toxicity declined over time as expected.

Conclusion: APBI demonstrates a favourable acute toxicity profile in DCIS patients, supporting its safety as a treatment