錦戸, 文彦  ,  高田, 英治  ,  盛武, 敬  ,  山谷, 泰賀

Introduction: Interventional radiology (IVR) is a medical subspecialty of radiology to realize image-guided surgical procedures using imaging modalities, such as X-ray fluoroscopy. However, skin injuries by prolonged X-ray exposure during such procedures have been reported[1]. Therefore, monitoring of skin dose is desired in clinical sites for reduction of excessive X-ray exposure. We are developing a real-time dose distribution monitoring system for the IVR in which only radiolucent materials are in the field-of-view so as not to interfere with the IVR procedure. Organic photodiodes (OPDs) are mainly composed of organic materials, which have good transparency for X-rays. As a result, the detector using OPDs combined with a plastic scintillator connected to a thin flexible cable is expected to have transparency to X-rays. These characteristics are suitable as X-ray detectors for IVR dose monitoring. We develop a new detector based on the plastic scintillator and OPD connected to the thin flexible cable for the real-time monitoring of skin dose distribution in IVR. X-ray dosimeter using OPD: The device structure of OPD is plastic scintillator (BC-408, 10 mm × 10 mm × 1 mm)/ IZO (100nm)/ PEDOT: PSS (30 nm) / PCBM: P3HT (200 nm) / Al (70 nm). The size of a sensing area is 6 mm × 4 mm on the plastic scintillator. Figure 1 shows photograph of the plastic scintillator and the OPD. A readout flexible board was made of 25 μm thick polyimide board and 12 μm thick copper wire. There are three readout electrodes to connect to the OPD electrode as shown in fig. 2. In order to keep the transparency, these electrodes and the OPD are contacted with carbon paste. Therefore, it is expected that many X-ray detectors can be mounted on the patient head to obtain dose distribustion. Experiment: We evaluated the X-ray detectors as a dosimeter for the IVR with a micro CT (R_mCT2, RIGAKU). The micro CT can obtain images in the projection mode, and change the tube current and change the X-ray tube position. We conducted an irradiation experiment using one readout board shown in fig.2 with the micro CT. Current from the sensing area was measured and recorded with a picoammeter (8240; ADCMT Corp.) and a windows-PC in 1 s recording interval. The OPD device was located at the center of the field of view. The X-rays were irradiated from the upside of the X-ray detector. Results: Figure 3 shows the averaged induced current in the OPD during 20 s as a function of the X-ray tube currents of 20, 40, 80, 120, 160 and 200 μA. Clear correlation between the X-ray tube current and induced current was observed. The current of the detector 2 was lower than others because connection between the OPD and the flexible calbe was not sufficent at that time. In addition, the induced current was proportional to effective X-ray energy and sufficient transparency was obtained. Conclusion: We tested the new prototype X-ray detector using a plastic scintillator and OPD. As a result, we obtained sufficient performance for X-ray irradiation in real-time with a 1 s interval.
MMND-ITRO Conference 2016参加・口頭発表

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