A comparison of kilovoltage and megavoltage cone beam CT in radiotherapy

Abstract

AbstractAs more and more patients are planned in 3D, the need to verify their position and treatment in 3D also becomes apparent. Megavoltage (MV) and kilovoltage (KV) cone beam computed tomography (CBCT) provide 3D verification of patient position. However, the soft tissue contrast and thus the accuracy of delineation is superior with KV CT imaging. CBCT in conjunction with energy fluence maps from electronic portal imaging devices (EPIDs) could theoretically be used to verify the dose delivered. In this instance, a cross calibration between the KV CBCT and the EPID would be required which would not be necessary with MV CBCT. Adaptive planning with CBCT poses similar challenges for both KV and MV CBCT. Although KV CBCT can produce images with Hounsfield units (HUs) comparable with conventional CT in homogenous phantoms there are large discrepancies in inhomogeneous mediums. If the cupping artefact is corrected for in MV CBCT, the HU values can compare well with KV CBCT for homogenous media. However, advances need to be made to achieve a lower patient dose with MV CBCT. At present, the lower dose required for KV CBCT allows for more frequent imaging and better image quality.