Siemens Healthineers' Varian business has published results from the FAST-02 clinical trial, finding that proton Flash radiotherapy provided pain relief for adults with thoracic bone metastases while producing no treatment-related serious adverse events.

The study builds on the earlier FAST-01 trial, which established the feasibility and safety of proton Flash therapy for bone metastases in the extremities. FAST-02 expanded the approach to metastatic lesions in the ribs, clavicle, scapula and sternum.

Conducted at the Cincinnati Children's/University of Cincinnati Proton Therapy Center, the trial enrolled 10 adult participants. Each received a single 8 Gy treatment delivered at dose rates exceeding 40 Gy per second. Researchers assessed safety by monitoring treatment-related adverse events and evaluated effectiveness using patient-reported pain scores collected one and three months after treatment.
Varian's ProBeam proton therapy system was modified to deliver the ultrahigh-dose rates required for Flash therapy, and its Eclipse treatment planning system was updated to support treatment planning. The company said the findings will help inform larger, multicenter clinical studies evaluating proton Flash radiotherapy across additional cancer types.

Among the eight participants who completed the three-month assessment, six (75%) reported complete pain relief and two (25%) reported partial pain relief. Of the two participants with one-month pain assessments who had not yet reached the three-month follow-up, one reported stable pain and the other reported a partial pain response.

"The significance of FAST-02 lies in our treatment sites being bone metastases within the thorax, meaning proximity to the lungs, heart and spinal cord," said Emily Daugherty, M.D., associate professor of radiation oncology at the University of Cincinnati Cancer Center. "Assessing critical organ side effects is essential for any future implementation of FLASH in deep-seated tumors. Importantly, the results continue to show that Flash effectively controls pain with minimal side effects, and there were no serious adverse events related to the treatment. Despite participants being treated for thoracic metastases, no cardiac or pulmonary toxicities were observed."

The FAST-01 and FAST-02 studies are the only published in-human clinical trials of proton Flash therapy to date.

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