Quality Assurance of Onboard Megavoltage Computed Tomography Imaging and Target Localization Systems for On- and Off-Line Image-Guided Radiotherapy

We reviewed the quality assurance procedures that have been used to test fan- and cone-beam megavoltage-based in-room imaging systems. Phantom-based tests have been used to establish the geometric accuracy and precision of megavoltage-based systems. However, the clinical implementation of any system is accompanied by challenges that are best tested in a clinical setting using clinical images. To objectively judge and monitor image quality, a set of standard tests and phantoms can be used. The image noise and spatial and contrast resolution have been assessed using standard computed tomography phantoms. The dose to the patient resulting from the imaging procedure can be determined using calculations or measurements. The off-line use of patient images is of interest for the evaluation of dosimetric changes throughout the treatment course. The accuracy of the dosimetric calculations based on the megavoltage images has been tested for the fan- and cone-beam systems. Some of the described tests are typically performed before the clinical implementation of the imaging system; others are suited to monitor the system's performances.