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Pediatric Radiology

Erschienen in:

01.04.2008 | Original Article

Computing effective doses to pediatric patients undergoing body CT examinations

verfasst von: Walter Huda, Kent M. Ogden

Erschienen in: Pediatric Radiology | Ausgabe 4/2008

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Abstract

Background

The computation of patient effective doses to children is of particular interest given the relatively high doses received from this imaging modality, as well as the increased utilization of CT in all areas of medicine. Current methods for computing effective doses to children are relatively complex, and it would be useful to develop a simple method of computing pediatric effective doses for clinical purposes that could be used by radiologists and technologists.

Objective

To obtain pediatric effective doses for body CT examinations by the use of adult effective doses obtained from effective dose (E) per unit dose length product (DLP) coefficients, and energy imparted to a child relative to an adult.

Materials and methods

Adult E/DLP coefficients were obtained at 120 kV using the ImPACT CT dosimetry spreadsheet. Patients were modeled as cylinders of water, and values of energy imparted to cylinders of varying radii were generated using Monte Carlo modeling. The amounts of energy imparted to the chest and abdomen of children relative to adults (R_en) were obtained. Pediatric effective doses were obtained using scaling factors that accounted for scan length, mAs, patient weight, and relative energy imparted (R_en).

Results

E/DLP values were about 16 μSv/mGy cm for males and about 19 μSv/mGy cm for females. R_en at 120 kV for newborns was 0.35 for the chest and 0.49 for the abdomen. At constant mAs, the effective dose to 6-month-old patients undergoing chest CT examinations was found to be about 50% higher than that to adults, and for abdominal examinations about 100% higher.

Conclusion

Adult effective doses can be obtained using DLP data and can be scaled to provide corresponding pediatric effective doses from body examinations on the same CT scanner.

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A 70-kg adult patient uniformly irradiated to 1 Gy absorbs 70 J of energy and receives an effective dose of 1 Sv (i.e. 14 mSv/J); a 35-kg patient uniformly irradiated to 1 Gy also receives 1 Sv but only absorbs 35 J (i.e., 28 mSv/J). In general, if the energy deposited is the same, and the patient mass is halved, organ doses and/or effective dose will double.

The E/DLP for an adult chest is 17.2 μSv/mGy cm when measured in a body phantom; DLPs obtained from dose measurements in head phantoms would be approximately double, but the E/DLP conversion factor would be approximately one-half. DLP is a measure of the total radiation incident on the patient, and the choice of phantom size is immaterial. It is only important to be consistent—one cannot quantify DLP using doses obtained with head phantoms and use E/DLP conversion coefficients using doses obtained with body phantoms.

Note that adults would normally be scanned at 120 kV; the DLP at 120 kV would be 347 mGy cm, which corresponds to an adult effective dose of 5.2 mSv.

We have assumed that the E/DLP is independent of the X-ray tube voltage. E/DLP factors have a modest kV dependence, and in cardiac imaging E/DLP conversion factors have been shown to be 10% lower at 80kV compared to 120 kV [34].

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Titel: Computing effective doses to pediatric patients undergoing body CT examinations
verfasst von: Walter Huda
Kent M. Ogden
Publikationsdatum: 01.04.2008
Verlag: Springer-Verlag
Erschienen in: Pediatric Radiology / Ausgabe 4/2008
Print ISSN: 0301-0449
Elektronische ISSN: 1432-1998
DOI: https://doi.org/10.1007/s00247-007-0732-6

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Springer Medizin

Computing effective doses to pediatric patients undergoing body CT examinations

Abstract

Background

Objective

Materials and methods

Results

Conclusion

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Springer Medizin

Abstract

Background

Objective

Materials and methods

Results

Conclusion

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