AbstractID: 8143 Title: Evaluation of a MOSFET Patient Dose Verification System for
CT Dosimetry
A Metal Oxide-Silicon Field Effect Transistor, MOSFET, patient dose verification
system is evaluated as to its application to patient CT dosimetry.
The viability of the MOSFET dosimeter for measuring entrance skin exposure in CT
examinations is evaluated with regard to sensitivity, reproducibility, energy dependence,
angular dependence and linearity with exposure and exposure rate. The system is
compared with TLD for accuracy as a tool for the real time evaluation of entrance skin
exposure in CT.
The sensitivity of the detectors was determined to be 11.2 mV per roentgen on the high
sensitivity setting. Reproducibility of each individual detector in CT application was
evaluated by repeated exposures at a fixed technique and was determined to be better
than 10%. Energy dependence was verified to be less than 10% for the CT energy range
from 80 to 140 kVp. The angular dependence was characterized by exposing the
detectors to a diagnostic x-ray beam rotated in 15° intervals perpendicular to the
detector’s axis. The detectors proved to be linear in response with exposure, as measured
with an ionization chamber, over a range from 0.5 to 3 R. The linearity of the system
versus exposure rate was characterized versus TLD on one second CT scans at various
tube currents. Finally, the system accuracy for the measurement of entrance skin
exposure in CT was evaluated by absolute comparison versus TLD on CT phantoms.
This characterization concludes that the MOSFET patient dose verification system is a
capable tool for measuring CT patient entrance skin exposure.