Shielding design for a PET imaging suite: a case study.

The introduction of positron emission tomography into the clinical environment presents the medical health physicist with another challenge to his/her shielding acumen. On one hand, elaborate models can be employed, but most of these are beyond the resources possessed by most institutions. On the other hand, one could perform the analysis using simplifying assumptions (e.g., point source geometry, with or without build-up). This kind of approach would likely overestimate the shielding requirements. Such over-design is not ALARA. In fact, over-design could place such tight engineering or cost constraints on a project as to make it untenable. Recently, this designer was faced with the need to design a PET imaging suite with both engineering and time constraints. This paper describes an approach using resources readily available to medical health physicists. By using the dimensions of the bottle manikin (BOMAB) phantom as a guide, a human-form source was developed. Combined with a point-kernel shielding code, the exposure environment was readily modeled and shielding recommendations developed. In addition, to validate the model, results from preoperational instrument surveys and integrating dosimeters are discussed.