| Most electronic portal imaging devices (EPIDs) developed so far use a Cu plate/phosphor screen to absorb x rays. The approach permits the use of a thin screen (∼2 mm thick) to obtain a high spatial resolution, however this results in a low quantum efficiency (QE) for high energy megavoltage (MV) x rays. In addition, the high atomic number (Z) phosphor results in an over-response of the detector to low energy x rays, corrupting the accuracy of dosimetric verification. My goal is to develop a high QE MV x-ray detector using a thick low-Z material. The approach converts x-ray energy into radiation-induced light (Cherenkov radiation) in a thick (∼ 10--30 cm) matrix of optical fibres aligned with the incident x rays, to dramatically improve the QE while maintaining a high resolution. This work demonstrates that the predominant light generation in optical fibres under high energy irradiation is indeed Cherenkov radiation. |
