ESTRO 2025 - Abstract Book

S635

Clinical - Breast

ESTRO 2025

4597

Digital Poster Boosting the breast surgical bed with FAST-forward scheme: advantages, efficacy and safety. Nerea Ugarte Ruiz de Aguirre, Carolina Ortiz Bautista, Francisco de Paula Titos Sánchez, Carmen Mesa Saenz, Carlos Miguez Sánchez, David Muñoz Carmona Radiation oncology, Hospital Virgen Macarena, Sevilla, Spain Purpose/Objective: Following the publication of the FAST-Forward (FF) trial, this regimen has become part of the standard of care in early breast cancer. It has shown no inferiority in disease control, reducing treatment time by a third without increasing side effects. Despite the change it has brought to clinical practice, there are some patients who can not benefit from this regimen due to the lack of information about safety and efficacy of the use of a boost with FF when risk factors are present. Various studies on accelerated partial breast irradiation have administered higher doses (28-30Gy) with good tolerance and results. Our hypothesis is that the addition of a simultaneous integrated boost (SIB) to the tumor bed does not increase toxicity while achieving better disease control in patients with risk factors. Material/Methods: Retrospective observational single-center study that compares patients treated during 2020 at the Hospital Virgen Macarena with the FF regimen, with or without boost to the breast. Results: A total of 123 patients were included in this analysis, of whom 40 (32.5%) received a Brest boost due to poor prognostic factors. In 95% of the patients, the boost was administered simultaneously and 5% sequentially, with a boost dose ranging from 29 (95%) to 30 Gy (5%). With a median followup of 44.3 months, no patient presented locoregional recurrence. Distant failure was observed in three patients. None of these patients belonged to the boost group. We recorded 10 deaths, of which only 2 were due to breast cancer. When we compare both groups (without versus with boost) there are no big distinctions attending to the adverse effects. Neither in acute locoregional toxicity (42.1% vs. 45%, p=0.92) nor chronic toxicity (9.6% vs. 16.2%, p=0.167). Similar rates of radiodermatitis, breast pain, edema, hyperpigmentation, telangiectasias, pruritus, fibrosis and ulceration at the breast level were observed (p>0.05). We observed an increase of the astenia G1-2 in the boost treatment group (acute: 13.1% vs. 20%, p=0.04, chronic: 0% vs. 2.6%, p=0.037). No toxicity >G 3 was recorded. Regarding cosmesis, there were no significant differences between groups (p > 0.05), with patients presenting not less than good cosmesis. Conclusion: The addition of boost to the FF regimen does not significantly increase overall toxicity , making it a safe procedure. Although the short followup has shown good disease control with no local recurrence. This could mean a benefit by reducing treatment time and thereby improving their quality of life.

Keywords: FAST-Forward boost SIB

References: Murray Brunt A, Haviland JS, Wheatley DA, et al. Hypofractionated breast radiotherapy for 1 week versus 3 weeks (FAST-Forward): 5-year efficacy and late normal tissue effects results from a multicentre, non-inferiority, randomised, phase 3 trial. Lancet. 2020;395(10237):1613-1626. doi:10.1016/S0140-6736(20)30932-6 Goldberg M, Whelan TJ. Accelerated Partial Breast Irradiation (APBI): Where Are We Now?. Curr Breast Cancer Rep. 2020;12(4):275-284. doi:10.1007/s12609-020-00384-x