Radiation shielding implications of computed tomography scatter exposure to the floor.

This article investigates whether CT scanners used primarily for either head or body work have scattered radiation levels that may impact shielding considerations. Several 35 x 43 cm film cassettes were used to cover the floor area around a General Electric Hi-Speed Advantage CT unit. Regions of maximum exposure were identified (visually with sensitometric confirmation). An ion chamber was used to obtain radiation exposure levels for typical head and body protocols. Greater scattered radiation was found behind the gantry for head scanning (20 vs. 16 microGy for a body scan) while greater scatter was observed in front of the scanner for body scans (46 vs. 31 microGy for the head scan). The resulting annual doses to the floor from typical workloads (assuming 32 cases a day) can be as great as 0.63 Gy for head protocols or 1 Gy from body work. Care may be needed to assure adequate shielding for floor areas near CT scanners specializing in either head or body work. Also, while increased throughput with helical scanners is currently x-ray tube heat limited, shielding plans should allow for enhanced heat capacity (and greater throughput) in future generation scanners.