S894
Clinical - Mixed sites & palliation
ESTRO 2026
6 Radiation Oncology, University of Pennsylvania, Philadelphia, USA. 7 Pediatrics, University of Cincinnati College of Medicine, Cincinnati, USA. 8 Radiation Oncology, New York Proton Center, New York, USA Purpose/Objective: FAST-01 established first in-human proton FLASH feasibility for extremity bone metastases with 8 Gy delivered at ≥ 40 Gy/s and a 66.7% site-level pain response at 3 months with only grade 1–2 toxicities. Extending proton FLASH from extremity sites into the lung-adjacent thorax, we assessed the safety and clinical workflow feasibility of single-fraction proton FLASH for symptomatic non-vertebral thoracic osseous metastases in a prospective trial. Material/Methods: FAST-02 (FDA IDE G220086) is a prospective, single- arm study using Varian FLASH-enabled ProBeam and Eclipse treatment planning systems to treat painful rib, scapula, sternum, or clavicle metastases. Co-primary endpoints are CTCAE v5.0 toxicity and pain relief at the treated site(s), with workflow metrics as secondary endpoints. Exclusion criteria included prior grade ≥ 2 radiation pneumonitis. Accrual opened February 2023 and last patient was treated in May 2025. Twelve patients were enrolled and 10 were treated. Compared with rectangular fields from a predefined library and treatment exclusively at gantry angle 0 for FAST-01, FAST-02 implemented patient-specific FLASH transmission plans generated in Eclipse, conformal uniform single-field delivery, and a full range of gantry angles. Results: Patient demographics and clinical characteristics are summarized in Table 1. All 10 treated patients completed FLASH per protocol with no dose delivery malfunctions. Although 2 device issues delaying treatment were reported, neither resulted in patient harm, and prespecified stopping rules were not triggered. Average patient time-on-table was 14.6 minutes, compared to 15.5 minutes for single treatment site patients in FAST-01. At a median follow- up of 189 days (range: 25-930 days), three patients reported transient grade 1 adverse events (erythema, hyperpigmentation) possibly- or definitely-related to treatment. There were no grade ≥ 2 acute or late adverse events at least possibly-related to FLASH (0/10). Pain response was recorded at 3 months follow-up in 8 patients and at 1 month follow-up in 2 patients. An overall pain response rate at the treatment site of 90% was observed (6 complete responses, 3 partial responses, 1 stable disease). Three patients (33%) reported pain flares (2-point increase in pain on 0-10 scale) by day 11 follow-up, which was comparable to rate of pain flares reported
the highest efficacy, with a response rate of 91%, compared with 66% and 25% for BED 39 Gy and 14.4 Gy schedules, respectively (p = 0.015).A significant increase in mean hemoglobin levels was observed, from 6.99 g/dL before radiotherapy to 10.52 g/dL after radiotherapy (p = 0.0001), along with a significant reduction in the mean volume of transfused red blood cells, from 750 mL to 225 mL (p = 0.003).The number of patients requiring transfusion was reduced by half (p = 0.008).Post-treatment evaluation showed three cases of rebleeding, with a mean recurrence interval of 2.5 months, and one death due to hemorrhagic shock after 10 months. Conclusion: Our study confirms the hemostatic efficacy of radiotherapy in the management of gastric cancers, with good treatment tolerance, consistent with findings from the literature [2–3]. References: [1] Lee YH, Lee JW, Jang HS. Palliative external beam radiotherapy for the treatment of tumor bleeding in inoperable advanced gastric cancer. BMC Cancer. 2017;17(1):541. doi:10.1186/s12885-017-3508- x[2] Mitsuhashi N, Ikeda H, Nemoto Y, Kuronuma M, Kamiga M, Hiroshima Y. Hemostatic Effect of Palliative Radiation Therapy in Preventing Blood Transfusions from Bleeding Occurring within Advanced Gastric Cancer. Palliat Med Rep. 2021;2(1):355-364. doi:10.1089/pmr.2021.0041[3] Tanaka O. Hemostatic palliative radiotherapy for gastric cancer: A literature review. Technical Innovations & Patient Support in Radiation Oncology. 2024;31:100266. doi:10.1016/j.tipsro.2024.100266 Keywords: Hemostasis, BED, tolerance Proffered Paper 3314 FAST-02: Second-in-human prospective clinical trial of proton FLASH—early safety and efficacy, workflow feasibility, and advances beyond FAST-01 Emily Daugherty 1,2 , Yongbin Zhang 1 , Zhiyan Xiao 1 , Lori Backus 3 , Julie M. McDonald 3 , Beth Stockman 3 , Jennifer Woo 4 , Claire McCann 4 , Ken Russell 4 , Ricky A. Sharma 4 , Dee Khuntia 4 , James L. McGee 5 , Jeffrey D. Bradley 6 , John Breneman 7 , Charles B. Simone, II 8 , John P. Perentesis 1,7 , Anthony E. Mascia 1,2 1 Cincinnati Children's/UC Proton Center, Cincinnati Children's Hospital, Cincinnati, USA. 2 Radiation Oncology, University of Cincinnati College of Medicine, Cincinnati, USA. 3 Pediatrics, Cincinnati Children's Hospital, Cincinnati, USA. 4 Medical Affairs, Varian, a Siemens Healthineers company, Palo Alto, USA. 5 Radiation Oncology, OSF Healthcare, Peoria, USA.
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