S215
Clinical - Breast
ESTRO 2026
Conclusion: The combination of RT and capacitive HT proved safe, feasible and well tolerated, with toxicity comparable to RT alone. Following completion of recruitment, HT has been incorporated into routine clinical practice at ICO for selected recurrent breast cancer cases. In this real- world setting, HT-related adverse effects remain mild (grade 1–2 skin burns), confirming that hyperthermia does not increase overall toxicity and represents an effective adjunct to improve local tumor control. References: Datta NR et al. Hyperthermia and radiotherapy in the treatment of breast cancer: a meta-analysis. Int J Hyperthermia. 2016;32(4):479-487.Kaidar-Person O et al. Re-irradiation and hyperthermia in breast cancer. Clin Oncol. 2017;29(8):539-545.De Colle C et al. Re- irradiation combined with hyperthermia in breast cancer: a systematic review. Cancers (Basel). 2022;14(3):563.Kok HP et al. Current state of the art of hyperthermia treatment planning: a review. Int J Hyperthermia. 2021;38(1):1235-1252.Sinha PM, Folefac CA, Overgaard J, Horsman MR. The rationale for combining hypofractionated radiation and hyperthermia. Cancers. 2024 Dec. Keywords: Hyperthermia, breast cancer recurrences Breast Reirradiation Practice Patterns: An International Survey from the Reirradiation Collaborative Group (ReCOG) Linda Hong 1 , Philip Poortmans 2 , Marianne Aznar 3 , Eric D Brooks 4 , Dana Casey 5 , J Isabelle Choi 6 , Stefanie Corradini 7 , Reshma Jagsi 8 , Dana Keilty 9 , Anne Koch 9 , Camilla Kronborg 10 , Marcin Kubeczko 11 , David McClatchy 12 , Marija Popovic 13 , Kilian E Salerno 14 , Simona F Shaitelman 15 , Manju Sharma 16 , Yat Tsang 9 , Charles Mayo 17 , Dorota Gabry ś 18 Digital Poster Highlight 712 1 Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA. 2 Radiation Oncology, Iridium Network and University of Antwerp, Antwerp, Belgium. 3 Radiation Oncology, University of Manchester, Manchester, United Kingdom. 4 Radiation Oncology, Premier Radiation Oncology Associates, Clearwater, USA. 5 Radiation Oncology, UNC School of Medicine, Chapel Hill, USA. 6 Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA. 7 Radiation Oncology, Friedrich-Alexander Universität Erlangen- Nürnberg, Erlangen, Germany. 8 Radiation Oncology, Emory University School of Medicine, Atlanta, USA. 9 Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 10 Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 11 Breast Cancer Unit, Maria Sk ł odowska-Curie National Research Institute of Oncology, Gliwice, Poland. 12 Radiation
Oncology, Massachusetts General Hospital, Boston, USA. 13 Medical Physics, The Ottawa Hospital, Ottawa, Canada. 14 Radiation Oncology Branch, National Cancer Institute, Bethesda, USA. 15 Radiation Oncology, University of Texas MD Anderson Cancer Centerancer Center, Houston, USA. 16 Radiation Oncology, University of California, San Francisco, San Francisco, USA. 17 Radiation Oncology, University of Michigan Medical School, Ann Arbor, USA. 18 Radiation Oncology, Maria Sk ł odowska-Curie National Research Institute of Oncology, Gliwice, Poland Purpose/Objective: Breast, chest-wall, and/or regional nodal reirradiation (reRT) is increasingly considered for locoregional recurrence or new primary breast cancer after prior radiotherapy (RT)(1, 2), yet practice patterns remain heterogeneous. This study reports an international survey by the Reirradiation Collaborative Group (ReCOG) (3) evaluating current clinical reRT practice patterns and existing knowledge gaps in optimal reRT approaches for breast cancer. Material/Methods: Radiation oncologists and medical physicists with expertise in breast RT completed a structured ReCOG survey between 02/2024 and 06/2025. Respondents were queried about patient selection criteria, factors influencing the choice between second breast- conserving therapy and mastectomy, reRT dose and fractionation schedules, preferred reRT dose guidance, planning methods, and key knowledge gaps that would impact clinical reRT decision-making. Results: 37 respondents participated from Europe (n=19), North America (n=14), and other geographies (n=4). The identifiable respondents represented 32 institutions. The most common reasons respondents omit or avoid reRT included high risk of major side effects from prior RT such as fibrosis or lymphedema (40%), short relapse interval (33%), or limited life expectancy (17%). When reRT is given, respondents answered that fibrosis (31%), pain (17%), and arm lymphedema (14%) are the side effects most impacting quality of life. Conventional fractionation (45–60Gy in 1.8–2Gy fractions, 23–30 fractions) was the most frequently selected reRT regimen, followed by moderate hypo-fractionated schedules (40Gy in 15 fractions). Only one respondent reported to use 40- 50Gy in 1.25-1.5Gy fractions BID. For reRT modalities, external-beam photon techniques were the most reported, with VMAT/IMRT preferred in recurrent breast and chest-wall disease, while protons and brachytherapy were used selectively based on availability and target volume. Hyperthermia was used by few (n=7). Most respondents (80%) reported performing plan summation with prior RT data when DICOM RT information was available, but approaches
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