Authors (including presenting author) :
Kwan KK(1), LO M(1)
Affiliation :
(1)Medical Physics Unit, Department of Clinical Oncology, Tuen Mun Hospital
Introduction :
Given financial costs and requirements of shielding PET/CT suites can be substantial, accurate assessment of needed barriers and whether it is necessary to extend such radiation shielding all the way to the ceiling become increasingly important as growing number of the suites are expected in HA pipeline.
Objectives :
Dose limit of non-radiation works in locations affected by the suite is limited to 1 mSv/year as for a member of the public. On a weekly basis, this means controlling the dose to the level of 20 µSv. Instantaneous dose rates at any uncontrolled access to the suite have to meet the licensing conditions from Radiation Board.
Methodology :
An iterative method for defining the shielding design is adopted from ISO standards 14152 - Neutron radiation protection shielding, including the steps of:
• Choice of radiation protection level and other design criteria;
• Characterization of radiation sources;
• Identification of constraints to implementation and building;
• Choice of shielding materials and arrangement within the shielding;
• Choice of calculation methods;
• Choice of the final solution;
• Experimental check.
Result & Outcome :
An instantaneous dose-rate plot to visually highlight areas of potentially high radiation exposure adjacent to the suite is stimulated. Excel spreadsheets are also derived to implement calculations of the barrier thickness from radiation transmission values in an analytical expression proposed by Archer et al. fitting the Monte Carlo transmission data stimulated by AAPM Task Group 108. Obvious site specific factors that affect the design are incorporated in the spreadsheets, these include:
• The number of patients imaged.
• The amount of radiotracer administered per patient.
• The length of time that the patient remains in the facility.
• The location of the facility.
Structural layout and logistical arrangements of a PET facility are different from other diagnostic imaging facilities. This is due to the high energy of positron annihilation radiation and the fact that patients are multiple sources of radiation throughout the imaging workflow. Meeting our objectives in radiation protection can be an expensive proposition. Systematic planning plus effective communications of design simulations/computations with the equipment vendor, facility architect, inspector, and among medical physicists/users are necessary to produce a cost-effective design while maintaining radiation safety standards.
