Dosimetric evaluation for workers operating into a PET department

Positron emission tomography (PET)is considered one of the most relevant diagnostic imaging technique having the peculiar characteristic to provide functional and quantitative information of the organ of interest. During the last five years, great efforts have been done to improve the diagnostic accuracy of this imaging modality through the development of new data acquisition/processing systems and the introduction of new β+ emitting radiopharmaceuticals increasing the interest of clinicians. The turning point in clinical PET development is represented by the introduction and FDA approval of 18 F-FDG as an oncological PET radiotracer. Nowadays, there is increasingly wide PET application for clinical diagnosis, even in centres without a cyclotron unit, thanks to the availability of 18F-FDG produced in licensed sites that are located within a reasonable distance of the imaging units. PET radiopharmaceutical are positron emitters with their characteristic 511 keV annihilation photons detected with coincidence systems. This high energy radiation poses different radiation safety problems in a conventional nuclear medicine department where usually more than 90% of examinations are performed with 90m Tc radionuclide emitting 140 keV photons. Particular attention is required on dealing with radioprotection aspects in PET facility to optimize absorbed dose for workers. A primary assessment of different levels of exposure dose due to both 99m Tc and 18F radionuclides is possible by considering the Γ values which clearly demonstrate the different safety concerns. However, to estimate the final dose absorbed by workers other variables should be considered as the workload, shielding, injected activity, in vivo uptake-clearance of the tracer, time spent by the operator to take care of the administered patient. Aim of this work is to present absorbed dose values, during a 1 year, of four workers, two physicians and two technologists, full time dedicated to the PET centre activities of the Ospedale Maggiore di Milano. In this centre and ECAT EXACT HR+state-of-the art-scanner (SIEMENS/CTI) is installed and 18F-FDG whole-body imaging represents the principal clinical activity (about 96% of patients workload). Some considerations on possible points susceptible of further improvements were also discussed in the mean to optimize the radioprotection programs. (Author)