Sci‐AM Fri ‐ 05: Shielding design for a PET‐CT simulator in a radiotherapy department

Abstract

Purpose: To design the shielding for a PET‐CT simulator in a radiation therapy department, and to verify the adequacy of shielding during acceptance testing. Method and Materials: A Discovery ST (GE Healthcare, Milwaukee, USA) PET‐CT scanner replaced a CT‐Simulator in our centre. Existing space was reconfigured to include a patient rest area for FDG uptake and a hot lab. Adjacent areas included a simulator control room, patient waiting rooms, and corridors; floors above and below contained offices and linac bunkers and control rooms. Patients were modeled as point sources; attenuation by concrete walls and lead shielding explicitly included build‐up. Design limits were set to 1 mSv per year for nuclear energy workers (NEWs), and 0.05 mSv per year for non‐NEWs. A linear 1.5‐GBq source of in scattering material was used to verify the adequacy of the shielding. Results: The control room was shielded with 6.35 mm of Pb. Two sheets of lead glass (48% Pb by weight) totaling 14 mm provided sufficient attenuation for a window. The patient uptake area and the scanner room were shielded with 4.7 mm of Pb on walls adjacent to corridors. No shielding was required on the floor and ceiling. Measurement showed that design goals were met. Conclusion: Strategic location of patients, NEWs, and low‐occupancy areas simplified design to these stringent limits. Careful consideration of workloads and occupancy factors are needed to meet the design criteria, particularly when older facilities are being redesigned. Design to such low limits unnecessarily increases construction cost.