Operational Radiation Safety for Pet-Ct, Spect-Ct, and Cyclotron Facilities

Abstract

Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are well- established and indispensable imaging modalities in modern medicine. State-of-the-art computed tomography (CT) scanners have now been integrated into multi-modality PET-CT and SPECT-CT devices, and these devices, particularly PET-CT scanners, are dramatically impacting clinical practice. 18F-fluorodeoxyglucose (FDG), by far the most widely used radiopharmaceutical for clinical PET imaging in general and oncologic PET imaging in particular, is highly accurate in detecting (approximately 90%) and staging many types of tumors, monitoring therapy response, and differentiating benign from malignant lesions. Several factors, including the relatively high administered activities [e.g., 370-740 MBq (10-20 mCi) of FDG], the high patient throughput (up to 30 patients per d), and in particular, the uniquely high energies (for a diagnostic setting) of the 511-keV positron-negatron annihilation photons, make shielding requirements, workflow, and other radiation protection issues important considerations in the design of a PET or PET-CT facility. The Report of Task Group 108 of the American Association of Physicists in Medicine (AAPM) provides a comprehensive summary of shielding design and related considerations, along with illustrative calculations. Whether in the form of a PET-CT or a SPECT-CT device, the introduction of CT scanners into a nuclear medicine setting has created new and complex radiation protection issues concerning the radiation burden and attendant risks accrued by patients undergoing such multi-modality procedures (especially in those instances in which higher-dose, diagnostic-quality CT studies are done as part of the PET-CT or SPECT-CT exam). In addition, because PET is dependent on the availability of short-lived 18F (Tp = 110 min) primarily in the form of FDG, and other short-lived positron emitters such as 11C (20 min), 13N (10 min), and 15O (2 min), cyclotrons for production of medically applied radionuclides and associated radiochemistry facilities are now widespread (well over 100 worldwide) and present their own radiation safety issues. In addition to the radioactive product, sources of exposure include neutrons and radioactive activation products in the various cyclotron components and surrounding shielding. Nonetheless, published studies have shown that the radiation doses to personnel working in cyclotron and associated radiochemistry facilities, as well as in PET or PET-CT and SPECT or SPECT-CT facilities, can be maintained below, and generally well below, the pertinent regulatory limits. This presentation will review the basic radiation safety aspects, including shielding and workflow, of these increasingly important and increasingly numerous facilities. The radiation burden accrued by the patients undergoing PET-CT or SPECT-CT exams will be considered as well.

A Proposed Simple Model for Estimating Occupational Radiation Dose to Staff from Veterinary 18F-FDG Pet Procedures

“…On the other hand, administered activities (dosages) are generally smaller for animal patients because they weigh less on average than human patients (Martinez et al 2012). Additionally, the patient throughput at a veterinary clinic (currently about 25 procedures performed every quarter at CSU) is much less than at a human imaging center (up to 30 patients a day) (Zanzonico et al 2008). Because of the differences between human and animal protocols, there is very little equivalent occupational dose data from human PET imaging.…”

“…Once injected into a patient, 18 F-FDG localizes in tissues proportionately to glycolytic activity (Phelps 2004) and therefore can sensitively detect hypermetabolic tissues including many types of malignant cancer (Zanzonico et al 2008;Workman and Coleman 2006). Although variable, the time allotted for 18 F-FDG uptake in humans is generally È60 min (Boellaard et al 2010).…”

Investigation of Staff Finger Doses During Quality Control of FDG Production

“…While whole-body radiation doses received by staff in nuclear medicine and PET clinics (Zanzonico et al 2008;Covens et al 2007;Sharma et al 2006;Eschner et al 2000;Ostertag et al 1991), cyclotron production facilities (Major 2009;Mishani et al 1999) and finger/extremity measurements within routine dispensing and handling of radiopharmaceuticals (Vanhavere et al 2008;Wrzesień et al 2008;Ginjaume et al 2007;Tandon et al 2007;Pant et al 2006;Saether et al 2005;Martin and Whitby 2003;Dhanse et al 2000) have been previously reported, the published data on finger/ extremity radiation doses received by staff performing routine quality control of 18 FDG is limited. Therefore, the aim of this study was to determine the finger/extremity doses received during this process and determine whether or not staff would need to be designated as classified radiation workers as a result of the work undertaken (Ionizing Radiation Regulations 2000).…”

Potential shielding for a positron emission tomography (PET) suite

“…This particular PET was designed as a conventional bismuth germanium scanner, taking approximately fifty minutes per whole body scan [2] . Since the annual number of nuclear medicine procedures has increased three-fold (from seven million to twenty million) between 1985 and 2005, a reasonable approach was to assume that the facility would remain busy throughout the year [7] . The facility would need to be taken out of service seven weeks each year for maintenance and calibration.…”