Development of a portable type open-window-ionization chamberin mammography

为了在乳腺X射线摄影中进行基于正确剂量测量值的精度管理，在乳腺X射线摄影设备的低能X射线剂量测量中，研制了响应特性不变的便携式开窗电离室。为了将其视为不同于常规自由电离室的便携式类型，考虑了集电极的形状和布置。采用能谱与乳腺X线筛查设备相同的剂量标准装置，对电离室实验模型进行了能量依赖性和绝对测量评价。剂量率依赖性的线性良好~15 mGys-1。在管电压23 ~ 110 kV的X射线能量范围内，探测器的响应变化小于3%。暗电流为10-14~-15A，并验证了长期稳定的测量值。采用新概念开发的便携式开窗电离室可在医疗设施中安装的乳腺X射线摄影设备中进行准确度管理所需的剂量评估的情况下实现高精度和稳定的测量。

In order to perform accuracy management based on the measurement value of the correct dose in mammography, in dose measurement of the low energy X-rays from mammography equipment , the portable type open-window-ionizationchamber which the characteristic of response does not vary was developed. In order to consider it as a portable type unlike the conventional free -ionization chamber, the shape of a collector electrode and arrangement were considered. The energy dependence and the evaluation of absolutely measurement of experimental model of an ionization-chamber were performed using the dose standard place with the same energy spectrum as the equipment used in mammography screening of X-rays. The linearity of dose rate dependence was good to ～15 mGys-1. In the energy range of the X-rays from tube voltage 23 kV to 110 kV, change of the response of a detector was less than 3 %. Moreover, dark current is 10-14～-15A, and it checked that the stable measurement value was obtained for a long time. The portable type open-window-ionization-chamber developed by a new concept can implement highly accurate and stabilized measurement in case of dose evaluation required for the accuracy management in the mammography equipment currently installed in medical facilities.