ESTRO 2023 - Abstract Book

S169

Saturday 13 May

ESTRO 2023

4 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics Unit, Milan, Italy; 5 Fondazione IRCCS Istituto Nazionale dei Tumori, Prostate Cancer Program, Milan, Italy; 6 Ospedale San Gerardo, Radiation Oncology, Monza, Italy; 7 Fondazione IRCCS Istituto Nazionale dei Tumori , Radiotherapy, Milan, Italy Purpose or Objective According to ASTRO and ESTRO guidelines, external beam Partial Breast Irradiation (PBI) is a valid option for early-stage Breast Cancer patients. Nevertheless, there is still a lack of consensus about the best treatment schedule. In this study, we aimed to collect data from patients who underwent PBI in one week. Materials and Methods We retrospectively analyzed survival and toxicity data of female patients treated in our institution from 2013 to 2022. Inclusion criteria were age ≥ 50 years, conservative breast surgery for non-lobular, G < 3, and luminal-like breast cancer with a maximum diameter of 20 mm without lymph nodal invasion. Gross Tumor Volume (GTV) was defined as the breast tissue between surgical clips; Clinical Target Volume (CTV) was an isometric expansion of 15 mm from the GTV, cropped into the homolateral breast; Planned Target Volume (PTV) was CTV + 5 mm of isometric expansion. The treatment schedule was 30 Gy delivered with VMAT in 5 daily fractions, prescribed at 95% of the dose to the PTV. ConeBeam Computed Tomography was used for IGRT. The primary endpoint was Local Control (LC). Disease Free Survival (DFS), Overall Survival (OS) and safety were secondary outcomes. Toxicities and cosmesis were analyzed sec. RTOG and Harvard scales, respectively. Results Three hundred eighty-one patients with a median age of 69 (33 – 91) years were included in the study. Characteristics are summarized in Table1. One hundred ninety-two (50.4%) of the cases were left breast; 360 (94.5%) were invasive ductal carcinomas, 10 (2.6%) were lobular invasive carcinomas, 10 (2.6%) were other histologies, and 1 (0.3%) was ductal in situ carcinoma; 368 (96.6%) were G1 or 2, and 4 (1.0%) were G3. Median dimension of the lesions was 8 mm (<1 – 30); 292 (76.6%), 86 (22.6%) and 3 (0.8%) were Luminal A, B and HER2-positive, respectively. After a median follow-up of 28 (6 – 104) months, 7 (2.0%) experienced local recurrence, of which two were “In field”. Among local relapses, 6 (85.7%) were not prescribed hormonal therapy, 1 (14.3%) did not complete radiation therapy, and 1 (14.3%) had an underpowered covering of the PTV (= 94.3%). Three-year LC, DFS and OS were 97.5% (95% C.I. 96.2% – 98.8%), and 96.9% (95% C.I. 95.7% – 98.1%) respectively. No ≥ G3 acute nor late toxicities were reported. There were 8 (2.1%) cases of G2 acute fibrosis, and 10 (2.9%) patients experienced G2 late toxicities. Five (1.5%) patients reported late cardiac major events, but 4 (80%) of them were treated on the right breast. Three (0.9%) late pulmonary toxicities were detected. Good or Excellent cosmetic evaluation sec. Harvard Scale was assessed in 252 (96.9%) cases by the physician VS 241 (89.2%) cases by the patients.

Conclusion Our dose prescription is the most sustainable choice for patients and hospitals. This study demonstrated that “One-week” PBI is also effective and safe. PD-0234 Single-fraction stereotactic radiotherapy for Partial Breast Irradiation using the Gammapod system M. Trovo 1 , C. Reverberi 1 , A. Prisco 1 , L. Seriau 2 , S. Bertozzi 2 , M. Bonotto 3 , M. Mansutti 3 , M. Orsaria 4 , E. Pegolo 4 , M. Guarnieri 5 , D. Marfisi 5 , V. Gagliardi 5 , E. Moretti 5 , P. Scalchi 5 , C. Zuiani 6 , C. Cedolini 2 1 Azienda Sanitaria Universitaria Udine, Radiation Oncology, Udine, Italy; 2 Azienda Sanitaria Universitaria Udine, Breast Surgery, Udine, Italy; 3 Azienda Sanitaria Universitaria Udine, Medical Oncology, Udine, Italy; 4 Azienda Sanitaria