ESTRO 2023 - Abstract Book

S628

Monday 15 May 2023

ESTRO 2023

OC-0762 Single fraction SBRT vs 3D-CRT for painful bone metastases: a single-blind phase 3 RCT (NCT03831243) C. Mercier 1,2 , C. Billiet 1,2 , G. De Kerf 1 , K. Vandecasteele 3,4 , P. Ost 1,4 , I. Joye 1,2 , P. Vermeulen 5,2 , L. Dirix 6 , Y. Lievens 3,4 , D. Verellen 1,2 , P. Dirix 1,2 1 Iridium Netwerk, Radiation Oncology, Antwerp, Belgium; 2 University Antwerp, Integrated Personalised and Precision Oncology Netwerk, Antwerp, Belgium; 3 University Hospital Ghent, Radiation Oncology, Gent, Belgium; 4 Ghent University, Department of Human Structure and Repair, Gent, Belgium; 5 GZA ziekenhuizen, Translational Cancer Research unit, Wilrijk, Belgium; 6 GZA Ziekenhuizen, Medical Oncology, Wilrijk, Belgium Purpose or Objective To test whether high-dose single fraction SBRT of 20 Gy to painful bone metastases is superior to standard 8 Gy 3D-conformal radiotherapy (3D-CRT) in achieving complete pain responses (CR). Materials and Methods In this single-blind, multicentre, randomised phase 3 trial, patients with up to 3 painful bone metastases were randomly assigned (1:1) to either a single SBRT fraction of 20 Gy or a single 3D-CRT treatment with 8 Gy. Inclusion criteria consisted of uncomplicated painful (worst pain score of ≥ 2 on a 0-10 pain scale) bone metastases arising from a solid tumour. The primary endpoint was the proportion of patients with a CR for pain at 1-month after RT, analysed as per intention-to-treat principle. Secondary endpoints included pain flare, re-irradiation need, toxicity (CTCAE version 5.0), quality of life (QoL). The study had 80% power to detect an absolute 25% improvement in 1-month CR rate from 25% to 50% in favour of SBRT. At the time of the current analysis, all patients completed 3 months of follow-up. The trial was registered on ClinicalTrials.gov (NCT03831243) and received funding from Kom Op Tegen Kanker. Results Between April 2019 and October 2022, 126 patients were randomised. Baseline characteristics were well-balanced between both arms (Table 1). In the SBRT group, three patients were unable to undergo SBRT. At one month, 16/63 (25%) patients achieved CR after 3D-CRT vs. 23/63 (37%) after SBRT (p=.25, Table 2). At 3 months, 15/63 (24%) patients achieved CR after 3D-CRT vs. 21/63 (33%) after SBRT (p=.32, Table 2). A per-protocol analysis of patients still evaluable after 3 months (87/126, 69%) showed a significantly higher CR after SBRT (21/39, 54%) compared to 3D-CRT (15/48, 31%, p=.048). Twenty-seven percent vs. 18% of patients experienced a post-radiation pain flare (p=.27). Re-irradiation of the painful lesion was indicated for 11% vs. 2% of patients (p=.06) in the 3D-CRT and SBRT arm, respectively. Grade 2-3 toxicity was observed in 14% and 15% in the 3D-CRT and SBRT arms, respectively, and no Grade ≥ 4 events occurred. QoL outcomes did not differ between the groups.