Abstract
BackgroundOrgan absorbed doses and effective doses can be used to compare radiation exposure among medical imaging procedures, compare alternative imaging options, and guide dose optimization efforts. Individual dose estimates are important for relatively radiosensitive patient populations such as children and for radiosensitive organs such as the eye lens. Software-based dose calculation methods conveniently calculate organ dose using patient-adjusted and examination-specific inputs.MethodsOrgan absorbed doses and effective doses were calculated for 429 pediatric 18F-FDG PET-CT patients. Patient-adjusted and scan-specific information was extracted from the electronic medical record and scanner dose-monitoring software. The VirtualDose and OLINDA/EXM (version 2.0) programs, respectively, were used to calculate the CT and the radiopharmaceutical organ absorbed doses and effective doses. Patients were grouped according to age at the time of the scan as follows: less than 1 year old, 1 to 5 years old, 6 to 10 years old, 11 to 15 years old, and 16 to 17 years old.ResultsThe mean (+/− standard deviation, range) total PET plus CT effective dose was 14.5 (1.9, 11.2–22.3) mSv. The mean (+/− standard deviation, range) PET effective dose was 8.1 (1.2, 5.7–16.5) mSv. The mean (+/− standard deviation, range) CT effective dose was 6.4 (1.8, 2.9–14.7) mSv. The five organs with highest PET dose were: Urinary bladder, heart, liver, lungs, and brain. The five organs with highest CT dose were: Thymus, thyroid, kidneys, eye lens, and gonads.ConclusionsOrgan and effective dose for both the CT and PET components can be estimated with actual patient and scan data using commercial software. Doses calculated using software generally agree with those calculated using dose conversion factors, although some organ doses were found to be appreciably different. Software-based dose calculation methods allow patient-adjusted dose factors. The effort to gather the needed patient data is justified by the resulting value of the characterization of patient-adjusted dosimetry.
Highlights
Organ absorbed doses and effective doses can be used to compare radiation exposure among medical imaging procedures, compare alternative imaging options, and guide dose optimization efforts
The sequential acquisition of positron emission tomography (PET) and computed tomography (CT) images in 2–18-Fluoro-2-deoxy-D-glucose (18F-FDG) PET-CT results in patient radiation dose from both imaging modalities but the risk incurred from this radiation dose is generally thought to be justified by the benefit of the diagnostic information obtained from the scan
All PET-CT examinations were performed with a GE Discovery 690 PET-CT, the CT portion comprised of a GE Lightspeed 16 CT unit
Summary
Organ absorbed doses and effective doses can be used to compare radiation exposure among medical imaging procedures, compare alternative imaging options, and guide dose optimization efforts. The wide range of reported PET-CT effective doses reflects varying conventions and technical parameters of use of CT in PET-CT examination, variations in injected 18F-FDG activity, range of patient age and body sizes as well as varying dosimetry methodologies. With radiation dose from each scan and multiple scans over the course of disease management, optimization of radiation dose in 18F-FDG PET-CT is especially important for children, who have longer life expectancy over which to undergo multiple scans and are generally thought to be more radiosensitive than adults [7]. The limitations of popular approaches to risk quantification are widely recognized In their overview of the debate surrounding the use of the linear nothreshold dose-response model, Zanzonico and Weber acknowledge that the uncertainty in correlation between diagnostic radiation dose and detriment propagates to the process of making clinical decisions for individual patients [15]
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