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BACKGROUND Resection (R) followed by single- or multi-fraction stereotactic radiosurgery (SRT) of brain metastases (BMs) lowers resection bed recurrence compared to R alone. Nevertheless, for larger BMs, 12-month recurrence rates after R+SRT can exceed 20–30%. Aiming to improve outcomes, a permanently implanted collagen tile brachytherapy device (GammaTile, GT Medical Technologies, Tempe, AZ) utilizing Cs-131 seeds embedded within a bioresorbable collagen tile was developed and is described as Surgically Targeted Radiation Therapy (STaRT) to distinguish it from external beam radiotherapy. STaRT allows rapid, intense localized radiation dose delivery directly to the tumor bed with predictable dosimetry immediately at the time of R, which may confer reduced risk for radiation necrosis compared to other therapies. It is hypothesized that R+ STaRT will increase surgical bed recurrence-free survival (SB-RFS), while reducing impact on functional and neurocognitive status compared to R+SRT. METHODS Multicenter, randomized, comparison trial of patients with resectable, previously untreated “index” BMs (≥ 2.5–5cm), and 0–3 other tumors, will be preoperatively randomized 1:1 to undergo R+SRT or R+STaRT to the index lesion; unresected tumors in both groups will receive SRT. Planned sample size is 180 from 14 sites. Enrollment opened 03/31/2021. First subject was enrolled 04/07/2021. Primary endpoint is SB-RFS. Secondary endpoints include overall survival, quality of life, neurocognition, functional status, imaging findings and adverse events. Follow-up will be through 24 months. This will be the first randomized trial comparing R+SRT versus R+STaRT delivered by Cs-131 sources in permanently implanted resorbable collagen tile carriers. Primary and secondary outcome measures captured will elucidate the potential risks and benefits of these two RT delivery methods in the setting of newly diagnosed BMs. We will present trial accrual progress, available data, experience and lessons learned.