Radiation dosimetry of ¹⁵O-water based on dynamic large-axial field-of-view positron emission tomography

Previously published effective dose coefficient estimates for ¹⁵O-water are around 1 μSv/MBq, resulting in an effective dose of around 0.4 mSv for a typically injected activity of 400 MBq in clinical cardiac scans. These estimates were based on limited positron emission tomography (PET) information combined with pharmacokinetic models. Large-axial field-of-view (LAFOV) PET allows for dynamic scanning of all relevant organs in a single scan and hence should result in more accurate dosimetry estimates. The aim of the present work was to estimate radiation dosimetry of ¹⁵O-water based on dynamic LAFOV PET.

Ten patients underwent 4 minutes 40 seconds dynamic PET scans after automated bolus injection of 350 ± 27 MBq ¹⁵O-water on a Quadra LAFOV PET scanner (Siemens Healthineers) at Turku PET Centre. All organs with visual uptake over background were segmented and time-activity curves were calculated and uncorrected for decay. Time-integrated activity coefficients (TIACs) were calculated by rectangular integration followed by exponential extrapolation. The remainder of the body TIAC was calculated as the theoretical maximum TIAC minus the sum of all source organs. Organ absorbed doses were calculated using IDAC-DOSE 2.1 and effective dose was estimated according to ICRP 103.

The highest TIACs were found in the lungs, liver, and brain, whereas the highest absorbed dose was found in heart wall, spleen, and kidneys. The sex-averaged effective dose coefficient was 0.62 ± 0.09 (mean ± standard deviation) μSv/MBq.

The effective dose of ¹⁵O-water is considerably lower than previously published values, amounting to an effective dose of approximately 0.25 mSv for a typical cardiac scan.