A novel wearable dosimeter system that can analyze the incident direction of X-rays for medical dosimetry – Improvements to the detector arrangements and analysis algorithm –

When performing real-time dosimetry using an active-type dosimeter during clinical fluoroscopic procedures, angular dependence of dosimeter response should be taken into account. Our research group addressed this issue and proposed a triple-type dosimeter that can determine the incident angle of scattered X-rays. The triple-type detector consists of three active dosimeters. The two side dosimeters have slope filters to enhance the angular dependence and are intentionally tilted. The central dosimeter faces forward. The incident angle of X-rays (θin) is estimated using the signal differences between the central dosimeter and the left and/or right dosimeters. Then, the absolute dose is determined by correcting the angular dependence of the central dosimeter based on the estimated θin. In order to verify the concept of the triple-type dosimeter, we conducted a proof-of-concept experiment using clinical X-ray fluoroscopic equipment. Scattered X-rays were generated by irradiating an elliptical cylindrical water phantom. The response of the triple-type dosimeter was evaluated by rotating it to vary the incident angle of scattered X-rays generated by the water phantom. The proposed dosimetry system could estimate the θin over an angular range of ±80° (with uncertainty of 1.35°), which is 30° wider than the previous version, and successfully determined the absolute doses after correction for the angular dependence of the dosimeter. Although the active-type dosimeter had a systematic uncertainty related to the angular dependence of ±15.2 %, our system succeeded in reducing the systematic uncertainty to ±3.2 %.