Preliminary safety evaluation of a cyclotron facility for positron emission tomography imaging

This work describes the design characteristics of a medical imaging centre which uses positron emission tomography, with a cyclotron for fluorine-18 a nd nitrogen-13 production, and which has provided experimental information on operational data recorded by area dosimetry since 1995. Doses to radioph armacy and medical staff have been measured both in normal work and in some handling incidents. Data on radiation levels in the installation have also been obtained and related to design details and shielding. Area dosimetry was carried out using a five-stationary detector network, with a sampling r ate of 2 min(-1), and by thermoluminescent dosimetry (TLD). Staff were also monitored by TLD, using extra chips for finger dosimetry and to duplicate individual whole-body dosimetry in order to measure doses in certain single operations. For normal work, average whole-body doses to radiopharmacy sta ff were between 0.03 and 0.28 mSv/month, wrist doses were between 0.42 and 2.67 mSv/month, and finger doses were between 1.4 and 7.7 mSv/day for the l eft hand and 0.8 and 2.4 mSv/day for the right hand; such variation reflect s the differing expertise of staff and the role played by optimisation. Fin ger doses between 16 and 131 mSv were measured in handling incidents, and f inger doses of 20.2 and 20.7 mSv for the left hand and 22.0 and 22.3 mSv fo r the right hand were measured during handling of a syringe without shieldi ng, containing 3 GBq. For medical staff, contributions to the whole-body do se of 2.0 and 1.9 mu Sv/procedure were measured for injection and placing t he patient on the examination couch, respectively. Dose measurement on the middle finger of the right hand gives an average of 70 mu Sv during the inj ection. The pro visions regarding the shielding design have proved to be ad equate and effective during a 3-year operational period. Operational doses to medical staff are comparatively low, while radiopharmacy staff are the m ost exposed. The finger doses in these professionals may exceed the annual limit, unless operational restrictions in daily pracntice are adopted. On-l ine area dosimetry records based on dose rate probes have proved to be effe ctive both for monitoring radiation levels during the operation and for det ecting changes in the behaviour of th facility in the irradiation process.