An operator positioning apparatus for a proton treatment system includes: a proton beam nozzle to emit a proton beam to a targeted region of a patient; a gantry wheel having a front face to support the proton beam nozzle to direct the proton beam to an isocenter of the gantry wheel corresponding to a center of the targeted region, wherein the gantry wheel rotates the proton beam nozzle around the isocenter; an active floor that horizontally translates across the front face of the gantry wheel, the active floor having an opening having a width through which the proton beam nozzle protrudes when the proton beam nozzle is located below the targeted region.