Abstract

This study measured the typical emitted radiation rate from the urinary bladder of PET patients after their scan and investigated simple methods for reducing the emitted radiation before discharge. 

Methods: The study included 83 patients (63 18F-FDG and 20 18F-NaF patients). Emitted radiation from the patients' urinary bladder was measured with an ionization survey meter at a 1-m distance, presuming the urinary bladder to be the primary source of radiation. The measurements were taken at different time points after PET image acquisition: immediate (prevoid 1), voided (postvoid 1), after waiting 30 min in the uptake room while drinking 500 mL of water (prevoid 2), and voided again (postvoid 2).

 Results: For 18F-FDG patients, the reduction of emitted radiation due to drinking water and voiding alone from prevoid 1 to decay-corrected postvoid 2 was an average of 22.49% ± 7.48% (13.65 ± 3.42 μSv/h to 10.48 ± 2.37 μSv/h, P < 0.001). For 18F-NaF patients, the reduction was an average of 25.80% ± 10.03% (9.83 ± 2.01 μSv/h to 7.23 ± 1.49 μSv/h, P < 0.001). 

Conclusion: In addition to the physical decay of the radiotracers, using the biologic clearance properties resulted in a significant decrease of the emitted radiation in this study. Implementing additional water consumption to facilitate voiding with 30 min of wait time before discharging certain 18F-FDG and 18F-NaF patients who need to be in close contact with others, such as elderly, caregivers, and inpatients, might facilitate lowering their emitted radiation by an average of 22%-25% due to voiding, not counting in the physical decay that should add an additional 17% reduction.

Keywords: ALARA; PET/CT; public safety; radiation exposure.