Cone-Beam Computed Tomography for Image-Guided Radiation Therapy of Prostate Cancer

Imaging plays a vital role in radiation therapy and with recent advances in technology considerable emphasis has been placed on cone-beam CT (CBCT). Attaching a kV x-ray source and flat panel detector directly to the linear accelerator gantry has enabled progress in target localization techniques, which can include daily CBCT set-up scans for some treatments. However, with an increasing number of CT scans there is also an increasing concern for patient exposure. An intensity-weighted region-of-interest (IWROI) technique, which has the potential to greatly reduce CBCT dose, in conjunction with the chord-based backprojectionfiltration (BPF) reconstruction algorithm has been developed and its feasibility in clinical use is demonstrated in this paper. A nonuniform filter is placed in the x-ray beam to create regions of two different beam intensities. In this manner, regions outside the target area can be given a reduced dose but still visualized with a lower contrast-to-noise-ratio (CNR). Image artifacts due to transverse data truncation, which would have occurred in conventional reconstruction algorithms, are avoided and image noise levels of the low and high-intensity regions are well controlled by use of the chord-based BPF reconstruction algorithm. The proposed IWROI technique can play an important role in image-guided radiation therapy (IGRT).