Document Type: Original Paper
Department of Medical Physics, Faculty of Health Science, Sefako Makgatho Health Science University, Pretoria, South Africa
Department of Medical Physics, Faculty of Medicine, Dr George MUkhari Hospital, Pretoria, South Africa.
University of free State Faculty: Health Sciences PO Box Bloemfontein 9300, Republic of South Africa
Introduction: The development of higher energy modalities in nuclear medicine such as positron emission tomography/computed tomography (PET/CT) has led to more complex shielding problems. This is due to several factors such as the radiopharmaceuticals relatively high-administered activity, the high patient throughput and the high energies of 511 kilo electron volt (keV) positron annihilation photons. This study therefore, aims to compare three different methods used to determine the required shield thicknesses of PET/CT facilities.
Methods and Materials: Shielding thicknesses for the hot-labs, uptake rooms and imaging rooms for all three facilities were done. A constraint design goal for this study was chosen as 6 mSv/year for radiation workers and 1 mSv for members of public for all three facilities. Occupancy factors (T) were established. All calculations had a use factor (U) of 1. The facilities workload (W) and thicknesses of all barriers were then calculated for the three facilities.
Results: For the broad beam approximations, the average thicknesses obtained were 9.56 mm of lead, 10.13 cm of concrete and 3.74 cm of iron for the hot-labs and 6.46 mm of lead, 6.70 cm of concrete and 2.44 cm of iron for the uptake rooms. For the Monte Carlo approximations, the average thickness obtained was 9.44 mm of lead, 12.46 cm of concrete and 3.55 cm of iron for the hot-labs and 6.64 mm of lead, 9.34 cm of concrete and 2.54 cm of iron for the uptake rooms.
Conclusion: Narrow beam approximations demonstrated the least shielding thickness required for the materials used in this study, which can lead to under-shielding. Broad beam and Monte Carlo approximations demonstrated higher shielding thickness required, although there were discrepancies between these two approximations for lead, concrete, and iron.