中文摘要：

目的探索多排CT的X射线束平面与电离室中心刻度偏移距离（offset distance,Do）对辐射剂量指数（CTDI100）测量结果的影响规律。方法采用满足IEC标准的头部体模（T6M164）和长杆电离室,测量Philips Brilliance iCT 256在轴扫条件下不同偏移距离时的CTDI100值。结果当偏移距离在1cm时,误差在0%～5%范围内;当偏移距离为3 cm,误差在5%～15%范围内;当偏移距离在5 cm时,误差在25%～75%范围内。结论 CTDI100测量结果对Do值敏感度较高,测量者在测量时应保证线束应与电离室中心刻度无偏离;在半影区内辐射剂量不容忽视,散射线束使得周围4点位的测量值较中心点发散,床对测量结果影响表现为中心点外的4个点位的CTDI100空间对称性降低。

英文摘要：

Objective To explore the influence law of offset distance（Do） between ionization chamber center scale and X-ray beam plane of multi-slices CT to the CTDI100 measurement result.Methods Head body mold（T6M164） and long pole ionization chamber,which meet IEC standards,are used to measure the CTDI100 value of Philips Brilliance iCT 256 on axial scanning condition of different offset distance.Results when Do is 1cm,relevant deviation（Dr） is 0%～5%,when Do is 3cm,Dr is 5%～15%,and when Do is 5cm,Dr is 25%～75%.Conclusion The measurement result of CTDI100 has greater sensitivity for Do,which means the operator should make sure no deviation exist between X-ray beam and ionization chamber center,besides,more attention should be paid to radiation dose in penumbra area.Scattering beam causes the measurement of CTDI100 at 4 points around more discrete,effect of bed to measurement result shows that symmetry of CTDI100 at 4 points outside the center reduces.