ABSTRACT
Until the early 1990s, film dominated the imaging procedures in radiation oncology treatment environments. Working with film was a cumbersome and time-consuming process not suitable for much of today's imaging procedures in radiation therapy. Most radiation therapy machines utilize a linear accelerator (LINAC) to generate the high-energy X-ray beam. When passing through the patient, the photons get absorbed. Due to the energy dependence of the X-ray cross section in a body, the low-energy part of the beam spectrum gets absorbed more heavily than the high-energy photons. The X-ray image is formed by individual photons that basically carry binary information. The incident high-energy photon is converted into an electron-hole pair in the photoconduction layer. A high voltage is applied between the top electrode and the pixel electrode in order to generate an electric field in the photoconductor. The photoconducting material used in many direct conversion detectors is amorphous Selenium.
