ESTRO 2022 - Abstract Book

S661

Abstract book

ESTRO 2022

Conclusion Public practice, older patients, less intensive treatment, and lower educational level were associated with worse survival outcomes in Brazilian breast cancer patients.

PD-0748 Local control and toxicity after hypofractionated accelerated palliative RT in breast cancer

K. Webb 1 , L. Gothard 2 , K. Mohammed 3 , A. Kirby 1,2 , I. Locke 1 , N. Somaiah 1,2

1 The Royal Marsden NHS Foundation Trust, Breast Unit, Sutton, United Kingdom; 2 The Institute of Cancer Research, Division of Radiotherapy and Imaging, London, United Kingdom; 3 The Royal Marsden NHS Foundation Trust, Research and Development Department, Sutton, United Kingdom Purpose or Objective For patients with locally advanced primary or recurrent breast cancer, radiotherapy (RT) is an effective treatment for loco- regional control. Hypofractionated RT is radiobiologically justified given the low α / β ratio of breast tumours and is convenient for patients due to fewer visits. 30-36Gy in 6Gy once-weekly fractions over 5-6 weeks is a common high-dose palliative regimen in breast cancer. A reduction in overall treatment time may lead to improved loco-regional control by limiting tumour cell repopulation, although it may increase acute toxicity. However, there are no data comparing local control and toxicity between once-weekly fractions and accelerated schedules of twice or more weekly fractions. Materials and Methods In this retrospective, single institution study, all patients receiving 30-36Gy in 6Gy fractions to an unresected breast cancer +/- involved lymph nodes between December 2011 and August 2020 were identified (nodal irradiation did not exceed 30Gy in 5 fractions to respect brachial plexus tolerance). Patients were grouped into once-weekly versus accelerated fractionation schedules. Response rates, local control and toxicity data were analysed. Results 109 patients were identified. Median follow-up duration was 46 months. 47 patients (43%) received once-weekly fractions and 62 patients (57%) received accelerated fractionation schedules (26, 24, and 12 patients received 2, 3 and 5 fractions a week, respectively). The majority of patients in both groups had T3/T4 disease (81% in once-weekly group; 88% in accelerated group) and had progressed on systemic treatments. 87% of patients had an objective (complete or partial) response to RT (81% in once-weekly group; 91% in accelerated group). Median time to local progression was 23.5 months overall (95% CI 17.8-29.2); 23.5 months (95% CI 18.8-28.1) in once-weekly group and 19.0 months (95% CI 7.0-31.1) in accelerated group (p=0.99). Acute toxicity of any grade occurred in 75% of patients (76% in once-weekly group; 74% in accelerated group), and grade 3 toxicity occurred in 7% of patients (7% in once-weekly group; 8% in accelerated group). There was no association between the groups and acute toxicity grade (p=0.779). Although late toxicity was only documented for 48 patients, there was no apparent association between the groups and late toxicity grade (p=0.263), although one grade 4 late toxicity (skin radionecrosis) occurred in a patient who received 5 fractions on consecutive weekdays. Conclusion There was no apparent difference in response rate, time to local progression or acute toxicity between patients who received once-weekly fractions and accelerated fractionation schedules. The accelerated regimens appear to be a safe alternative to the once-weekly regimen, may be preferred by patients and may also minimise interruptions to concurrent systemic therapy.

PD-0749 Systemic treatment and ablative therapies in oligometastatic breast cancer: a single center analysis

G. Glemarec 1 , J.L. Lacaze 2 , B. Cabarrou 3 , R. Aziza 4 , E. Jouve 5 , S. Zerdoud 4 , E. De Maio 2 , C. Massabeau 1 , M. Loo 1 , V. Esteyrie 1 , M. Ung 2 , F. Dalenc 2 , F. Izar 1 , C. Chira 1