Heavy PETting: reducing radiation exposure from intradepartment positron emission tomography scans.

Increasingly, positron emission tomography (PET) scans are being utilized in radiation medicine departments for staging, treatment planning, and follow-up. Positron emission tomography scans use signals emitted from the radioactive tracer [F]-fluoro-2-deoxy-Dglucose (FDG-glucose) that is preferentially taken up by cancer cells. After image processing including fusion with simultaneously obtained computed tomography (CT) scans, the oncologist is able to identify tumors as they “light up.” Positron emission tomography scans are becoming a part of standard oncologic evaluation for many cancers for which their sensitivity and specificity for cancer detection is superior to CT scans. Positron emission tomography is used frequently at the time of simulation because treatment planning can be tailored by targeting areas of metabolically active tumor. Given the sensitivity of PET in cancer detection, it is being used increasingly as part of standard followup to evaluate response to treatment, to detect early recurrent or persistent disease, and to help differentiate radiation necrosis from tumor. With all these useful applications in our cancer patients, the number of PET scans ordered has risen significantly in the last few years. For example, taking just the US Veterans Administration patients treated in our department, the number of PET scans ordered increased from 100 scans in 2008 to 811 in 2012. This presents a new and unique problem in radiation protection. The FDG-glucose is administered intravenously at a typical dose of 5-10 mCi directly before scanning, and it remains in a patient’s circulation for several hours after administration, with a physical half-life of 110 minutes. The biologic half-life is dependent on urinary excretion. Given patient anxiety in cancer detection and the fact that PET scanners are often located in close proximity to the ordering radiation oncologist, physician visits are