Purpose: To test whether dose-escalated single fraction (SF) stereotactic body radiotherapy (SBRT) of 20 Gy to painful bone metastases is superior to conventional SF three-dimensional (3D) conformal radiotherapy (RT) to a standard dose of 8 Gy in achieving complete pain response (CR).
Methods: A single-blind, randomized, controlled, phase III trial (ROBOMET) included 126 patients with up to three painful bone metastases, randomly assigned between April 2019 and October 2022 at multiple centers in Belgium. Inclusion criteria were uncomplicated painful bone metastases (worst pain score ≥2 on a 0-10 pain scale) arising from a solid tumor. Treatment consisted of either a single SBRT fraction of 20 Gy or a single conventional RT fraction of 8 Gy. The primary end point was the proportion of patients with a CR 1 month after RT scored according to the International Consensus on Palliative Radiotherapy Endpoints analyzed as per an intention-to-treat principle.
Results: After 1 month, 16 of 63 (25% [95% CI, 15 to 38]) patients treated with conventional RT achieved CR versus 23 of 63 (37% [95% CI, 25 to 50]) treated with SBRT (P = .25). After 3 months, 15 of 63 (24% [95% CI, 14 to 36]) patients achieved CR after conventional RT versus 21 of 63 (33% [95% CI, 22 to 46]) after SBRT (P = .32). Among patients evaluable after 3 months and treated per protocol, the SBRT group had more complete responders (21/39, 54% [95% CI, 37 to 70]) than the conventional RT group (15/48, 31% [95% CI, 19 to 46]; P = .048).
Conclusion: SBRT failed to demonstrate improved CR rates after 1 month.
Trial registration: ClinicalTrials.gov NCT03831243.