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Patient Radiation Doses from Adult and Pediatric CT

¹ Department of Radiology, SUNY Upstate Medical University, 750 E Adams St., Syracuse, NY 13210-2306.
² Present address: Department of Diagnostic Imaging, Rhode Island Hospital, Providence, RI 02903.

OBJECTIVE. The purpose of our study was to determine typical organ doses, and the corresponding effective doses, to adult and pediatric patients undergoing a single CT examination.

MATERIALS AND METHODS. Heads, chests, and abdomens of patients ranging from neonates to oversized adults (120 kg) were modeled as uniform cylinders of water. Monte Carlo dosimetry data were used to obtain average doses in the directly irradiated region. Dosimetry data were used to compute the total energy imparted, which was converted into the corresponding effective dose using patient-size-dependent effective-dose-per-unit-energy-imparted coefficients. Representative patient doses were obtained for scanning protocols that take into account the size of the patient being scanned by typical MDCT scanners.

RESULTS. Relative to CT scanners from the early 1990s, present-day MDCT scanners result in doses that are 1.5 and 1.7 higher per unit mAs in head and body phantoms, respectively. Organ absorbed doses in head CT scans increase from 30 mGy in newborns to 40 mGy in adults. Patients weighing less than 20 kg receive body organ absorbed doses of 7 mGy, which is a factor of 2 less than for normal-sized (70-kg) adults. Adult head CT effective doses are 0.9 mSv, four times less than those for the neonate. Effective doses for neonates undergoing body CT are 2.5 mSv, whereas those for normal-sized adults are 3.5 mSv.

CONCLUSION. Representative organ absorbed doses in CT are substantially lower than threshold doses for the induction of deterministic effects, and effective doses are comparable to annual doses from natural background radiation.

Keywords: MDCT • pediatric CT • physics of radiology • radiation dose

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