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Erschienen in:
01.05.2012 | Original Article
KERMA ratios in pediatric CT dosimetry
Erschienen in: Pediatric Radiology | Ausgabe 5/2012
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Background
Patient organ doses may be estimated from CTDI values. More accurate estimates may be obtained by measuring KERMA (Kinetic Energy Released in Matter) in anthropomorphic phantoms and referencing these values to free-in-air X-ray intensity.
Objective
To measure KERMA ratios (RK) in pediatric phantoms at CT.
Materials & methods
CT scans produce an air KERMA K in a phantom and an air KERMA KCT at isocenter. KERMA ratios (RK) are defined as (K/KCT), measured using TLD chips in phantoms representing newborns to 10-year-olds.
Results
RK in the newborn is approximately constant. For the other phantoms, there is a peak RK value in the neck. The median RK values for the GE scanner at 120 kV were 0.92, 0.83, 0.77 and 0.76 for newborns, 1-year-olds, 5-year-olds and 10-year-olds, respectively. Organ RK values were 0.91 ± 0.04, 0.84 ± 0.07, 0.74 ± 0.09 and 0.72 ± 0.10 in newborns, 1-year-olds, 5-year-olds and 10-year-olds, respectively. At 120 kV, a Siemens Sensation 16 scanner had RK values 5% higher than those of the GE LightSpeed Ultra.
Conclusion
KERMA ratios may be combined with air KERMA measurements at the isocenter to estimate organ doses in pediatric CT patients.