Abstract
BackgroundRadiation dose metrics vary by the calibration reference phantom used to report doses. By convention, 16-cm diameter cylindrical polymethyl-methacyrlate phantoms are used for head imaging and 32-cm diameter phantoms are used for body imaging in adults. Actual usage patterns in children remain under-documented.ObjectiveThis study uses the University of California San Francisco International CT Dose Registry to describe phantom selection in children by patient age, body region and scanner manufacturer, and the consequent impact on radiation doses.Materials and methodsFor 106,837 pediatric computed tomography (CT) exams collected between Jan. 1, 2015, and Nov. 2, 2020, in children up to 17 years of age from 118 hospitals and imaging facilities, we describe reference phantom use patterns by body region, age and manufacturer, and median and 75th-percentile dose–length product (DLP) and volume CT dose index (CTDIvol) doses when using 16-cm vs. 32-cm phantoms.ResultsThere was relatively consistent phantom selection by body region. Overall, 98.0% of brain and skull examinations referenced 16-cm phantoms, and 95.7% of chest, 94.4% of abdomen and 100% of cervical-spine examinations referenced 32-cm phantoms. Only GE deviated from this practice, reporting chest and abdomen scans using 16-cm phantoms with some frequency in children up to 10 years of age. DLP and CTDIvol values from 16-cm phantom-referenced scans were 2–3 times higher than 32-cm phantom-referenced scans.ConclusionReference phantom selection is highly consistent, with a small but significant number of abdomen and chest scans (~5%) using 16-cm phantoms in younger children, which produces DLP values approximately twice as high as exams referenced to 32-cm phantoms
Highlights
The rapid rise over the last few decades in computed tomography (CT) imaging and consequent population exposure to ionizing radiation, a known carcinogen, have raised concerns about the levels and variability of radiation doses across patients, institutions and countries, as well as the need for dose optimization [1,2,3,4,5,6,7,8]
16-cm diameter cylindrical polymethyl-methacyrlate phantoms are used for head imaging and 32-cm diameter phantoms are used for body imaging in adults
Using data from a large multicenter CT dose registry, this study describes variations in practice and differences in estimated doses that result from the differential use of 16-cm and 32-cm phantoms in young patients
Summary
The rapid rise over the last few decades in computed tomography (CT) imaging and consequent population exposure to ionizing radiation, a known carcinogen, have raised concerns about the levels and variability of radiation doses across patients, institutions and countries, as well as the need for dose optimization [1,2,3,4,5,6,7,8]. Dose optimization tools like diagnostic reference levels use metrics such as the volume CT dose index (CTDIvol), reflecting the average dose (per slice) over the total volume scanned for the selected CT conditions of operation, and Pediatric Radiology the dose–length product (DLP), reflecting the total dose imparted to the patient While these metrics reflect scanner output and not patient absorbed dose, they correlate closely with absorbed doses and help physicians and imaging practices compare their doses to a uniform standard [11]. Materials and methods For 106,837 pediatric computed tomography (CT) exams collected between Jan. 1, 2015, and Nov. 2, 2020, in children up to 17 years of age from 118 hospitals and imaging facilities, we describe reference phantom use patterns by body region, age and manufacturer, and median and 75th-percentile dose–length product (DLP) and volume CT dose index (CTDIvol) doses when using 16-cm vs 32-cm phantoms. Conclusion Reference phantom selection is highly consistent, with a small but significant number of abdomen and chest scans (~5%) using 16‐cm phantoms in younger children, which produces DLP values approximately twice as high as exams referenced to 32‐cm phantoms
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