Radiation dosimetry for electron beam CT.
OBJECTIVE
To measure the radiation dose profile, multiple-scan average dose (MSAD), and computed tomography dose index (CTDI) for electron beam CT and to determine the accuracy of ionization-chamber and manufacturer estimates of patient dose.


METHODS
High-resolution dose profiles along the longitudinal axis were acquired at several positions within the scan plane with use of radiographic film. The full-width-at-half-maximum values, peak radiation dose, CTDI, and MSAD were calculated from the digitized film profiles. CTDI was also measured with an ionization chamber.


RESULTS
The full-width-half-maximum value of the radiation profiles were significantly wider than the nominal scan width for the 6-mm single-section and 8-mm multisection modes. In the single-section mode, the CTDI underestimated the MSAD by 15%-30%. The multisection radiation profile was nonuniform and asymmetric.


CONCLUSIONS
Patient doses in electron beam CT are approximately 125% of the ionization-chamber CTDI measurements in the single-section mode. For the multisection mode, the average patient dose over the scan volume is approximately 70%-85% of the ionization-chamber CTDI measurements.
McCollough
C H
CH
Department of Diagnostic Radiology, Mayo Clinic, Rochester, MN 55905.
Zink
F E
FE
Morin
R L
RL
D006801:Humans; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed