MO‐E‐L100J‐03: Development of a Novel Electronic Portal Imaging Device Based On Cherenkov Radiation

Abstract

Purpose: Most electronic portal imaging devices (EPIDs) developed so far use a Cu plate/phosphor screen to absorb x rays. The main problem with this approach is that the Cu plate/phosphor screen must be thin (∼ 2 mm) in order to obtain a high spatial resolution, resulting in a low quantum efficiency (QE) for megavoltage (MV) x rays (typically 2–4%). In addition, the phosphor screen contains high atomic number (high‐Z) materials, resulting in an over‐response of the detector to low energy x rays in dosimetric verification. Our goal is to develop a new high QE MV x‐ray detector made of a low‐Z material for both geometrical and dosimetric verification in radiotherapy. Method and Materials: Our approach uses radiation‐induced light (Cherenkov radiation) in optical fibers that are made of low‐Z materials. With our approach, a thick (∼ 10–30 cm) fiber‐optic taper consisting of a matrix of optical fibers aligned with the incident x rays is used to replace the thin Cu plate/phosphor screen to dramatically increase the QE. The feasibility of this approach has been investigated using a single optical fiber embedded in a solid material. The spatial resolution expressed by the modulation transfer function (MTF) and the signal‐to‐noise ratio of the proposed detector at low doses (∼ one Linac pulse) have been measured. Results: It is predicted that, using this approach, a detective quantum efficiency (DQE) of an order of magnitude higher at zero frequency can be obtained while maintaining a reasonable MTF, as compared to current EPIDs. Conclusion: This work demonstrated the feasibility of using Cherenkov radiation for portal imaging applications [Work supported by the Individual Discovery Grant Program awarded by National Sciences and Engineering Research Council of Canada (NSERC)].