A study of the use of flat‐panel imagers for radiotherapy verification (in English)

Abstract

This thesis investigates the feasibility of the application of flat‐panel imagers (FPIs) based on amorphous silicon to radiotherapy verification. Intensity modulated radiotherapy imposes new demands on verification procedures. A contrast resolution of 1% may be required from portal imaging systems to resolve the target structure and the organs at risk (OAR). Furthermore a spatial resolution of 1 mm is desired. The imaging characteristics, spatial resolution, efficiency, and noise characteristics of the FPI for megavoltage imaging were investigated regarding these demands. Possible improvements from scatter rejection by a modified detector design were investigated by simulating the spectral response of the converter plates of these detectors to photons of different energies and the response to scattered photons. Since low contrast objects like the target structure and the OAR can be detected in radiographic transmission images only for some rare cases, tomographical imaging was tested for position verification. This was also done using an FPI and the megavoltage (MV) source of the treatment accelerator. A different approach to position verification is the integration of kilovoltage (kV) computed tomography (CT) into a clinical linear accelerator. Although this approach has higher demands on the hardware side, it will deliver higher contrast images at a lower dose. A comparison of MVCT and kVCT and an outlook to new possibilities using integrated CT therefore completes this thesis.