ESTRO 2023 - Abstract Book

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ESTRO 2023

presentation, but also to patients with T1 and T2 disease with 1-3 nodes positive at the time of axillary node clearance in presence of a high-risk feature e.g. grade 3, triple negative, HER 2 positive cancers to further decrease LR. References (1) Hypofractionated versus conventional fractionated postmastectomy radiotherapy for patients with high-risk breast cancer: a randomised, non-inferiority, open-label, phase 3 trial. Lancet Oncol. 2019; 20: 352-360

PO-1260 SBRT in metastatic breast cancer: in search of better outcomes

M. Rodriguez Pla 1 , G. Líria Fernandez 1 , M. Jordá Girones 2 , R. Garcia Gomez 2 , E. Jordá Sorolla 2 , M. Maroñas Martin 2 , M. Soler Rodriguez 2 , A. Ciafre Lucena 2 , D. Dualde Beltrán 2 , E. Ferrer Albiach 2 1 Hospital Clinico Universitario de Valencia, Radiation Oncology, Valencia , Spain; 2 Hospital Clinico Universitario de Valencia, Radiation Oncology, Valencia, Spain Purpose or Objective Stereotactic body radiotherapy (SBRT) has experienced exponential development in recent years, as its ablative capacity has demonstrated a benefit in certain patients including oligometastatic (OM) patients. The main objective of this study is to describe local control (LC), progression free survival (PFS) and overall survival (OS) in metastatic breast cancer patients treated with 3D-conformal conventional radiation therapy (RT3D) and SBRT. Materials and Methods From 1 January 2020 to 31 December 2021, 53 patients with metastatic breast cancer were treated with RT3D or SBRT technique. Insufficient follow-up (under two months), reirradiations and central nervous system involvement were causes of exclusion. Different immobilization systems were used as well as different regimens depending on the technique: 8-30Gy in 1-10 fractions for RT3D and 24-50Gy in 3-5 fractions for SBRT. We retrospectively reviewed demographics and clinical patient outcomes. Patients treated with RT3D had worse performance status and more metastatic lesions than SBRT patients. Patients were divided in two groups based on RT technique (RT3D vs SBRT) and OS, LC and PFS were analyzed. OS and PFS were assessed with Kaplan-Meier analysis. QUANTEC and UK consensus constraints were applied. Results 53 patients were analyzed. 40 patients were treated with RT3D and only 10 with SBRT. Median age was 58 years (32 – 83). Median follow-up was 10 months (3- 26). LC was achieved in 100% and 78% of the patients in the SBRT and RT3D group respectively. Cumulative probability of PFS was 39% (95% CI 22-55%) and 63% (95% CI 22-87%) at 12 months in RT3D and SBRT group, respectively. In the RT3D group, cumulative probability of overall survival was 78% (95% CI 61-88%) at 6 months and 56% (95% CI 38-71%) at 15 months. In the SBRT group cumulative probability of overall survival at 6 months and at 15 months was 100%. Kaplan-Meier OS and PFS analysis are shown in Figure 1 and 2. Grade ≥ 3 toxicity according to CTCAEv.5 was not observed. Conclusion Patients with oligometastatic or symptomatic metastatic breast cancer are candidates for higher local doses of radiation. SBRT has shown promise in LC, PFS and OS in these patients with an acceptable toxicity. There are currently ongoing phase III studies that will provide stronger evidence. Purpose or Objective Adjuvant radiation therapy for locally advanced breast cancer is part of the standard treatment to reduce local recurrence and death rates. Acute radiodermatitis is one of the most common side effects and bolus is a known predictive factor of it. In clinical practice many centers are hesitating to use bolus with hypofractionation. The purpose of this study is to show the effect of bolus in acute radiodermatitis in breast cancer patients treated with moderately hypofractionated radiation therapy. Materials and Methods In our prospective study we enrolled all T4 breast cancer patients treated with moderately hypofractionated radiation therapy (40Gy/15 fractions) after mastectomy. From 2016 to 2021 a total of 168 patients were irradiated at our Oncology Service. Standard 3D-CRT technique was used and a bolus of 5mm was applied daily. Chemotherapy was administered to all patients. Acute toxicity was evaluated using the RTOG scale. We monitored patients during radiation therapy, at the end of treatment, two weeks, one month, and two months after radiation therapy. Results The median age of the series was 54 years (range 31-83). Histology was invasive ductal carcinoma (90%), invasive lobular carcinoma (6%), and mixt (4%). The rates of acute grade 1, grade 2, and grade 3 radiodermatitis was 28% (n=47), 7% (n=12), and 4% (n=7), respectively. No treatment interruption was recorded. We did not find any significant correlation between chemotherapy regimen, endocrine therapy, nodal irradiation, higher BMI, or any other patient comorbidity, and higher grade of radiodermatitis. PO-1261 Radiodermatitis after bolus use in breast cancer patients treated with moderate hypofractionation E. Kozma 1 , A. Bodeci 1 , E. Gashi 1 , H. Nina 1 1 University Hospital Mother Teresa, Oncology, Tirana, Albania

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