ESTRO 2023 - Abstract Book

S1003

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ESTRO 2023

clinicaltrials.gov (NCT04679454) and was approved by institutional Ethical Committee (identification number 1308). Inclusion and exclusion criteria are summarized in Table 1. Results From 8/11/2021 to 9/9/2022 a total of 9 patients matching the inclusion criteria were enrolled and treated within the phase I study. Median age was 63.3 years (range 52.5–75.6). At a medium follow up of 6 months (range 1–11) no Grade>2 acute toxicity was observed. All patients underwent 3 breast MRI:before ablative RT,immediately before surgery,ex-vivo MRI on the excised tumor. Median time to surgery was 33 days (range 28–36). No post-surgical complications were reported. All patients showed a decrease of the KI-67 labeling index between the pre-RT core biopsy and the surgical specimen. No complete pathological response was achieved. Five out of 9 patients had BCS and received post-operative RT to the whole breast. The whole breast RT treatment planning was modified in 2 patients: in one to underdose a lung infiltrate due to asymptomatic radiological pneumonitis, found at the time of CT simulation scan, and in the other one to underdose the part of a rib in order not to exceed the maximum cumulative dose according to the constraints.

Conclusion Since no Grade>2 toxicity was observed and no dose limiting toxicity was reached, the phase I study comprised the minimum number of 9 patients and the 24 Gy dose step will be used for the treatment in the Phase II study. Data on late toxicity,molecular and pathologic assessment of RT-induced changes to study apoptosis, hypoxia, lymphocitic response and gene expression profile are being collected.

PO-1254 Moderate hypofractionated radiation therapy in inoperable breast cancer

M. Valero 1 , C. De la Pinta 1 , M.E. Centelles 1 , F.L. Mesa 1 , E. Fernández 1 , R. Hernánz 1 , M. Martín 1 , M.T. Muñoz 1 , M. Alarza 1 , J.A. Domínguez 1 , A. De Cózar 1 , M. Camacho 1 , J. Azcona 1 , S. Sancho 1

1 University Hospital Ramón y Cajal, Radiation Oncology, Madrid, Spain

Purpose or Objective Surgery is the gold standard in breast cancer treatment. In inoperable patients we purpose use hypofractionated palliative treatment. The aim of the study was to test if moderate hypofractionated radiation therapy is effective in symptomatic control of this inoperable breast cancer while decreasing toxicity. Materials and Methods Patients with symptomatic breast cancer were treated from September 2005 to March 2022 with moderate hypofractionated scheme. We created a database including the following variables: age, sex, histology, stage, radiotherapy dose, toxicity and progression. We performed a descriptive analysis of toxicities and local control (LC) and we analyzed overall survival (OS), disease-free survival (DFS) using Kaplan-Meier survival analysis. Results 37 patients were included. Median age at diagnosis was 85 (range 41-102). Stage I 22,2%, stage II 30,6%, stage III 2.8%, stage IV 44.4%. All patients received 30 Gy, 21 patients (56.8%) in 5 fractions daily, 16 patients (43.2%) in 6 fractions daily. 11 (29.7%) presented skin toxicity. 10 (27%) had acute skin toxicity, toxicity grades consisted of 4 patients (10.8%) grade 1, 4 (10.8%) grade 2 and 3 (5.4%) grade 3. 3 (8.1%) had chronic toxicity grade 1. Local control was analyzed based on RECIST criteria: 17 patients (45.9%) have stable disease; 11 patients (29,7%) partial response and 9 patients (24.3%) progressed. Local control rate at 1 and 3 years were 66.7% and 4.2%. Progression was located in brain (2); skin (2); lymph node (2); bone (2); liver (2) and carcinomatous lymphangitis (1).

Median time to progression from RT was 11 months. Median OS, DFS and LC were 25, 25 and 10 months.

Conclusion Employing moderate hypofractionated may be considered as an effective technique in palliative setting with local control and low toxicity in these patients.

PO-1255 Toxicity analysis of breast cancer patients treated with VMAT and 3D-CRT

J. Seppälä 1 , K. Vuorinen 2 , N. Miettinen 3 , J. Heikkilä 1 , M. Tengström 1