Positron emission mammography (PEM) imaging: Radiation exposure to technologist

Objectives PEM allows the identification of smaller breast malignancies compared to whole body positron emission tomography, but requires the technologist to be in close proximity to the patient for positioning, thereby receiving radiation exposure. To evaluate what levels of exposure the technologist might be receiving, three methods were used; computer modeling, lab simulation and technologist dosimetry measurements.

Methods Computer modeling used MicroShield® software with a 10 mCi 18F-FDG patient injection dose, and technologist to patient phantom distances of 2 feet for 8 minutes and 5 feet for 30 minutes. Lab simulation used 3 trapezoidal phantoms, each with 2 mCi 18F-FDG, modeling the FDG reduction with patient voiding prior to scans. Measurements replicated 1 minute for patient preparation at 15 inches, 2 minutes at 15 inches for injection site scan, 13 minutes at 15 inches for breast positioning, and 32 minutes of scanning time for technologist to observe the patient at 10 feet. Technologist dosimetry measurements were obtained at 3 sites with the technologist wearing a digital dosimeter zeroed prior to the start of each PEM scan.

Results The MicroShield program calculated the dose to the technologist to be 1.1 mrem per procedure. The lab simulation produced an estimated dose to the technologist of 1.7 mrem. Clinical measurements found an average dose of 1.3 ± 0.8 mrem per scan.

Conclusions A single 10 mCi 18F-FDG dose is known to result in a 700 mrem radiation exposure to the patient. Using this dose, our studies suggest the technologist receives an average of 1.3 mrem per scan. To exceed the NRC 5,000 mrem limit, a technologist would have to perform over 3,850 scans per year. These data show that the radiation exposure to the technologist is well within NRC limits. Further reduction in radiation is achievable by reducing injected dose, optimizing the workflow, and maximizing the technologist distance to the patient