2025-2026 MCW Radiation Oncology Annual Report - Flipbook - Page 7
2025-2026 Medical College of Wisconsin, Radia琀椀on Oncology Annual Report
dose-sparing characteris琀椀cs also contribute to reduced treatment-related toxici琀椀es and improved long-term
survivorship outcomes.
At the core of the proton therapy system is a compact cyclotron incorpora琀椀ng an 8.5-tesla superconduc琀椀ng
magnet, mounted directly to a rota琀椀ng gantry with the full gantry assembly weighing approximately 222,000
pounds. The Mevion S250i is a pencil beam scanning proton therapy system, in which a narrow proton beam is
magne琀椀cally steered with high precision. This delivery method is analogous to the opera琀椀on of an older
cathode-ray tube television, where a focused electron beam was rapidly scanned across the screen to form an
image. In a similar manner, electromagne琀椀c scanning magnets steer the proton beam spot-by-spot and layerby-layer, allowing the prescribed dose to be accurately “painted” throughout the target volume.
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