摘要
目的 研究不同乳腺剂量仪在单一能量X射线时的角响应性能,以及不同能量X射线时乳腺剂量仪角响应的变化趋势,对乳腺数字体层合成摄影（DBT）中受检者乳腺平均剂量的评价进行探讨.方法 分别用4种低能标准射线质对4种不同类型乳腺剂量仪进行照射,照射角度从0°至90°变化.每个角度重复曝光3次,记录4种剂量仪的测量值并计算该角度相对于垂直入射时的角响应值.结果 4种剂量仪的剂量响应均在射线垂直人射探测器表面时最大,随着射线入射角度的增大,其剂量响应逐渐降低.射线入射角为10°时,剂量仪A、B、C和D的角响应分别为0.99、0.99、0.96和0.96;入射角为25°时,分别为0.96、1.00、0.78和0.52.电离室剂量仪角响应曲线下降较为平缓,半导体探测器剂量仪的角响应曲线在角度较大明显下降,当射线入射角度大于45°时已检测不出剂量信号.对于电离室剂量仪,在角度不变时,射线能量较低时通常角响应值也较低.结论 在进行DBT系统中剂量测量时,现有的方法会低估乳房表面接受的实际剂量,进而低估了受检者的乳腺平均剂量.为使因球管旋转角度带来的误差降至最低,应该针对不同DBT设备对不同类型乳腺剂量仪进行相应角响应校正.
Objective To study the angular dependence of four different mammographic dosimeters to monoenergetic X-ray beams and observe the variation tendency in angular dependence to different energy X-rays and to discuss the evaluation of average glandular dose（AGD）in digital breast tomosynthesis（DBT）system.Methods One ionization chamber and three semiconductor dosimeters were exposed by four kinds of beam quality.The signal of each dosimeter was tested over an angular range of 0° to 90°.The dosimeters were exposed for three times at each selected angular position.The measurement at each angle was normalized to the appropriate measurement at perpendicular incidence.Results The responses from all the dosimeters had a maximum at 0° and decreased with increasing angles.When the radiation incidence angle was 10°,the angular dependence were 0.99,0.99,0.96 and 0.96 for dosimeters A,B,C and D,respectively.And the angular dependence decreased to 0.96,1.00,0.78 and 0.52 when the incidence angle was up to 25°.For semiconductor dosimeters,no signal was recorded when incidence angle was beyond 45°.For ionization chamber,the magnitude of the angular dependence generally decreased with increasing energy.Conclusions All of the dosimeters will underestimate the dose if used in DBT.In order to minimize the error due to the rotation angle of X-ray tube,correction factor of mammography dosimeter should be used for the measurement of AGD in DBT systems.
出处
《中华放射医学与防护杂志》
CAS
CSCD
北大核心
2013年第5期540-543,共4页
Chinese Journal of Radiological Medicine and Protection
关键词
乳腺数字体层合成摄影
乳腺剂量仪
角响应
校正因子
乳腺平均剂量
Digital breast tomosynthesis
Mammographic dosimeters
Angular dependence
Correction factor
Average glandular dose
