Some of the key features and functionality of the Proteus ONE are highlighted, including 220 degrees of gantry rotation, a robotic patient positioning system, cone-beam imaging, and pencil-beam scanning. With the Proteus ONE, facilities can start on the path to Proton Therapy now, and add additional capability as their case loads warrant. The Proteus ONE from IBA will help make proton therapy much more accessible to cancer facilities and their patients who could benefit from this promising technology.