An unrecognized occupancy change in the vicinity of a medical linear accelerator

It seems obvious that if a significant increase in occupancy occurs in the immediate vicinity of any radiation room a reexamination of the adequacy of the shielding should be performed. We discuss a facility where a new building was constructed in close proximity to an existing medical linear accelerator and no consideration was given to the consequences of that construction as it might impact the doses received by occupants of the new structure. For more than 10 years some areas in that building may have received exposures greater than the allowed regulatory limit. The situation reported here should serve as a cautionary tale for those who have the responsibility for providing radiation protection at any site where new construction or increases in occupancy might require a reanalysis of the previously designed radiation shielding.