For the purpose of this chapter, the following terms shall have the meaning indicated:
PRIMARY PROTECTIVE BARRIER is a barrier to attenuate the useful beam.
SECONDARY PROTECTIVE BARRIER is a barrier to attenuate stray radiation.
STRAY RADIATION is radiation not serving any useful purpose, which includes leakage and scattered radiation.
USEFUL BEAM is the radiation which passes through the window, aperture, cone or other collimating device of the tube housing.
The operator’s station at the control shall be behind a protective barrier either in a separate room, in a protected booth or behind a shield which will intercept the useful beam and any radiation which has been scattered only once.
Provision shall be made for the operator to observe and communicate with the patient without leaving the shielded position at the control panel. When an observation window is used, it must provide radiation attenuation equal to that required in the surrounding barrier.
All wall, floor and ceiling areas that can be struck by the useful beam, plus a border of 1 foot (305 mm), shall be provided with primary protective barriers.
Equipment operating above 50 kVp shall conform with the following:
- The control station shielding shall either be an integral part of the building or anchored to the building.
- The control station shall be provided with a window having radiation attenuation equal to that required by the adjacent barrier, or a mirror system, or a closed-circuit television viewing screen. The patient area must be visible to the operator without having to leave the protected area during exposure.
Equipment operating above 150 kVp shall conform to the following:
- The treatment room shall be provided with interlocks so that when any door of the treatment room is opened, either the machine will shut off automatically or the radiation level within the room will be reduced to an average of not more than 2 milliroentgens per hour and a maximum of 10 milliroentgens per hour at a distance of one meter in any direction from the target. After such shutoff or reduction in output, it shall be possible to restore the machine to full operation only from the control panel.
- The control station shall be within a protective booth or in an adjacent room.
A minimum of one door shall be provided with an auxiliary means for being opened in case of power failure or mechanical breakdown, where large power-driven doors offer the only access to the room.
A flashing red warning signal light energized only when the useful beam is on shall be located adjacent to the entrance(s) to a therapy room with equipment capable of operating above 500 kVp.