| Megavoltage computed tomography (MVCT) and megavoltage cone beam computed tomography can be used for visualizing anatomical structures prior to radiation therapy treatments to assist in patient setup and target localization. These systems provide images using the same beam used for patient treatment, however their image contrast is limited by the low detective quantum efficiency (DQE) of the detectors currently available. By using higher DQE thick, segmented cadmium tungstate detectors we can improve the system contrast. This in turn would permit enhanced soft tissue visualization, allowing MVCT to be more useful.;This thesis describes the evaluation of a prototype MVCT system that uses thick, segmented detectors. The system was found to be able to easily visualize a 15 mm diameter 1.5% contrast target with 2 cGy of radiation dose delivered. This system could become the basis for improved commercial MVCT systems. |
