S250-FIT Proton Beam Radiation Therapy Device (S250-FIT)

The Mevion S250-FIT is a proton beam radiation therapy system designed to deliver therapeutic proton radiation to patients with localized tumors and other radiation-susceptible conditions. It uses a 230 MeV superconducting synchrocyclotron accelerator with pencil beam scanning modality, and positions patients in a seated or perched upright position rather than supine. The device includes integrated CT imaging, treatment planning software, and a hardwired safety system.

The S250-FIT uses the same 230 MeV superconducting synchrocyclotron accelerator, usable energy range (30–230 MeV), beam delivery modality (pencil beam scanning), dose rate (2 Gy/min), and beam specifications as the predicate S250i. Key differences are: patient positioning (upright vs. supine), imaging (integrated CT vs. 2D X-ray), range shifter material (boron-carbide ceramic vs. polycarbonate), and addition of discrete arc planning and remote motion features. Maximum patient load differs (330 lbs vs. 400 lbs).

IEC 60601-2-64 (ion beam safety), IEC 62667 (ion beam performance), IEC 60601-2-68 and IEC 60601-2-44 (X-ray/CT), IEC 60601-1-3 (radiation protection), IEC 60825-1 (laser safety), IEC 62304 (software development), IEC 62366-1 and IEC 60601-1-6 (human factors), ANSI/AAMI SW96:2023 (cybersecurity), and FDA guidance documents on interoperability and device software.

Both the S250-FIT and predicate S250i are therapeutic proton beam systems with identical indications for use, the same accelerator type and beam performance specifications, and equivalent beam delivery mechanisms. Although the S250-FIT differs in patient positioning (upright rather than supine) and imaging modality (CT rather than 2D X-ray), testing demonstrated that upright positioning does not compromise radiation beam delivery and that treatment plans achieve substantially equivalent dosimetric coverage and clinical acceptability across multiple anatomical sites. The same verification and validation testing protocols used for the S250i were applied to the S250-FIT, confirming that differences in configuration do not raise different safety or effectiveness questions.