Development of a reconstruction methodology for the X-Ray spectrum of a medical LinAc positioning flat panel

This work analyzes the possibility of using the kV flat panel detector of a medical radiotherapy LinAc for consistency verification of X-ray beam generation in order to perform a quality assurance (QA) protocol. For directly measuring the energy spectrum of X-ray tubes is highly complicated due to the pile up effect produced by the high fluence of photons emitted, we have considered the possibility of using the flat panel detector covered with a PMMA wedge to obtain a gradient dose curve corresponding to specific working conditions of this LinAc X-ray tube. The relation between the gray level curve registered by the flat panel image and the primary X-ray spectrum emitted is defined by a first order Fredholm integral equation. Normally this function can be approximated by a response matrix, which can be obtained by means of Monte Carlo simulations. Obtaining the measured gray level curve and the response matrix, the primary X-ray spectrum can be unfolded via mathematical algorithms. With this approach, we propose a novel method that uses the kV flat panel detector available on LinAc for X-ray generator test. This spectrum reconstruction methodology reduces the inefficiencies and irregularity associated with using third-party QA detectors while allowing an automated procedure.