 FAST-01 is a prospective, single-center trial designed to assess the workflow feasibility, toxicity, and efficacy of flash therapy for the treatment of painful bone metastases in the extremities using a flash-enabled variant pro-beam proton therapy unit. The primary endpoints include assessing the workflow feasibility and toxicity of flash treatment, while the secondary endpoint is pain response at the treated sites. Initial results are expected to be published in 2022. This article was authored by Emily C. Doherty, Anthony Massia, Yong Zhong, and others.