I. J. Choi1,2, C. Hardy Abeloos3, A. Lozano4, M. Kim4, A. Hanlon4, C. E. Vargas5, J. H. Maduro II6, J. A. Bradley7, B. Offersen8, B. G. Haffty9, M. Pankuch10, R. A. Amos11, N. Kim12, Y. Kirova13, and R. W. Mutter14; 1Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 2New York Proton Center, New York, NY, 3Department of Radiation Oncology, NYU Langone, New York, NY, 4Center for Biostatistics and Health Data Science, Department of Statistics, Virginia Tech, Roanoke, VA, 5Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ, 6Department of Radiation Oncology, University of Groningen, University Medical Centre Groningen, Groningen, Netherlands, 7University of Florida Health Proton Therapy Institute, Jacksonville, FL, 8Aarhus University Hospital, Aarhus, Midtjyllan, Denmark, 9Rutgers Cancer Institute of New Jersey, Department of Radiation Oncology, New Brunswick, NJ, 10Northwestern Medicine Proton Center, Warrenville, IL, 11Department of Medical Physics & Biomedical Engineering, University College London, London, United Kingdom, 12Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea, Republic of (South), 13Department of Radiation Oncology, Institut Curie, Paris, France, 14Department of Radiation Oncology, Mayo Clinic, Rochester, MN
Purpose/Objective(s): Proton beam therapy (PBT) technology has advanced and become increasingly available over the past two decades. The extent to which PBT is employed for breast cancer (BC) is not known. This international survey of PBT centers was developed to determine the current state of PBT for BC. We hypothesized that PBT is used in a small but growing proportion of highly-selected patients with primary and recurrent BC at PBT centers. Materials/
Methods: An IRB-approved 29-question survey instrument was developed by the Particle Therapy Co-Operative Group (PTCOG) Breast Subcommittee addressing overall utilization of PBT for BC, technology, patient selection criteria, dose-fractionation regimens, and clinical trial enrollment. We identified all active PBT centers worldwide as of 2/2023 from the PTCOG Facilities in Operation webpage. Surveys were sent via SurveyMonkey in 6/2023, and responses collected from 6/2023-8/2023. Descriptive statistics were used to summarize responses, with comparisons by continent performed using Fisher’s exact tests. Results: Of 79 surveys distributed, 28 recipients submitted responses, corresponding with a 35.4% response rate. Fifteen (53.6%) of respondent centers were from the U.S., 8 (28.6%) from Europe, and 5 (17.9%) from Asia. Eighteen (64.3%) self-classified as academic institutions. 89.3% have pencil beam scanning, and 21.4% have passive scattering technology. 85.7% have CT image guidance capabilities. All but two centers (7.1%) are actively treating BC patients. Regional nodal irradiation (RNI) was the most common indication for PBT in 57.2%; for RNI, 46.2% use a hypofractionated regimen, and 42.3% use standard fractionation. Hypofractionation is the preferred RNI regimen in most European centers (87.5%) vs. 50% in Asia and 21.4% in the U.S. (p=0.003). 80.8% use PBT to deliver reirradiation. The most common patient selection methods were practitioner determination/patient preference (57.1%), comparative plan evaluation (53.6%), institutional guidelines (39.3%), and DVH modeling (32.1%). 82.1% also have photon capabilities; of these, 60.9% treat <10% of all BC patients with PBT, and 30.4% treat 10% to 49% of BC patients with PBT. In 42.3% of centers, =75% of BC patients treated with PBT are enrolled on a research study. The absolute number of BC patients treated with PBT to date was significantly different between the U.S., Europe, and Asia, with more U.S. centers (71.4%) reporting =100 patients treated vs. 37.5% in Europe and none in Asia (p=0.001). Conclusion: The utilization of PBT for BC varies at PBT centers across the globe. Comparative plans and DVH modeling were commonly employed as part of patient selection, and the most common indications were RNI and reirradiation. These survey data serve as a benchmark to establish the current global state of PBT use for breast cancer. Successor surveys will provide insight into the evolution of practice patterns.
