Speaker
Description
Introduction: The most PET devices contain scintillation crystals based on lutetium - LSO or LYSO. Lutetium Lu-175 is incorporate with radioactive Lu-176 (abundance 2.6%; T1/2=(3.56±0.07)×1010 years; β- radiation (Emax=596keV), followed by three simultaneous γ-ray emissions (energies: 88, 202 and 307keV)). Taking into account long half-life, lutetium activity could be considered as constant - 52.61±0.36Bq/g.
Objective: The objective is to estimate the amount of radioactive lutetium in Siemens Biograph 40 64 PET-CT device, potential impact on the diagnostic information and to emphasize the importance of remediation, to protect environment.
Methods: Based on the dimensions of the crystal, mass number and the total number of crystals, it was estimated the share of isotope Lu-176 in the overall mass, and the associated radioactivity.
Results: According to the device technical specification, it was determined the detector size and calculated the mass of detector unit - 2,368g. Furthermore, there are 169 crystals per detector block and 144 detector blocks, which leeds to the total detector mass - 57627g, from which the share of Lu-176 is 1150g. Hence, there is ring distributed radioactivity of about 60.5kBq.
Conclusion: Natural radioactivity of lutetium poses no problem in clinical PET imaging (excitation activities ~100MBq, energy threshold 350keV), but could have influence on the QC examinations with low activities, with Ge-68 point source (activity ~5kBq), and potentially at the end of dynamic studies using C-11 or O-15. After replacement of the detector block or termination of device exploitation, the proper disposal is mandatory.
