Abstract
Most electronic portal imaging devices (EPIDs) developed so far use a Cu plate/phosphor screen to absorb x rays. This approach uses a thin screen (∼ 2 mm) to obtain a high spatial resolution, however this results in a low quantum efficiency (QE) for megavoltage (MV) x rays (typically 2–4%). The phosphor screen also contains high atomic number (high‐Z) materials, resulting in an over‐response of the detector to low energy x rays in dosimetric verification. Our overall goal is to develop a new high QE MV x‐ray detector made of a low‐Z material for both geometric and dosimetric verification in radiotherapy. The approach is based on converting x‐ray energy into Cherenkov radiation in optical fibers. The design uses a thick (∼ 10–30 cm) matrix of optical fibres (to dramatically improve the QE) aligned with the incident x rays. This work investigates the characteristics of radiation‐induced light in optical fibers and demonstrates that the predominant light source in optical fibers under high energy irradiation is indeed Cherenkov radiation. Thus, the feasibility of using Cherenkov radiation as the primary light source in the proposed Cherenkov detector is validated. This work was supported by the National Sciences and Engineering Research Council of Canada (NSERC).
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