長尺シンチレーションファイバ線量計によるX線CT検査時における積分線量飽和値の測定

抄録

Measurement of the saturated dose integral for x-ray CT examination was done by using a newly developed scintillating fiber dosimeter with a long detection length of 880 mm, by inserting it into a human chest phantom. The saturated dose integral measured for the chest phantom, which was composed of MixDp and cork for the lung, was 2.4 mGy under the x-ray irradiation conditions used in lung cancer screening tests. The dose values measured were about 30% greater than those obtained with conventional CT ion chambers because of the large dose distribution outside the effective length of 100 mm of CT ion chambers. The reason of the large dose distribution outside the beam position of x-ray CT devices was examined with 3 mm-thick lead absorbers inserted into the chest phantom and surrounding the phantom. It was found that the large dose distribution was due to the scattering of x-rays in the phantom and that the contribution of x-ray leakage from CT devices was negligible. When absorbed doses are measured with conventional CT ion chambers, it is recommended that they be multiplied by a factor of 1.3 to obtain saturated dose integrals for x-ray CT devices.