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: Development of higher energy modalities 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 radiopharmaceutical relatively high-administered activity, high patient throughput, and high energies of 511 kilo-electron volt (keV) positron annihilation photons. Therefore, this study aimed to compare three different methods used to determine the required shielding thicknesses of PET/CT facilities.
Material and Methods: The required shielding thicknesses for three facilities were determined by using three different shielding methods, i.e. narrow beam, broad beam and Monte Carlo approximation. The design goal was chosen as 6 mSv/year for radiation workers and 1 mSv/year for the public. In addition, occupancy factors (T) were established, and all calculations had a use factor (U) of 1. The workload (W) of facilities and thicknesses of all barriers were then calculated for the three facilities.
Results: For narrow beam approximation the average required thicknesses obtained were 6.16 mm lead, 5.12 cm concrete and 2.95 cm iron. Broad beam approximation required an average of 7.55 mm lead, 8.01 cm concrete and 2.96 cm iron thicknesses. Monte Carlo approximation required 7.62 mm lead, 10.59 cm concrete and 2.94 cm iron thicknesses.
Conclusion: The narrow beam approximation demonstrated the least shielding thickness required for the materials used in this study, which can lead to under-shielding. The broad beam and Monte Carlo approximations demonstrated higher required shielding thickness although there were discrepancies between these two approximations for lead, concrete, and iron.