title: A performance comparison of flat-panel imager-based MV and kV cone-beam CT.
abstract: The use of cone-beam computed tomography (CBCT) has been proposed for guiding the delivery of radiation therapy, and investigators have examined the use of both kilovoltage (kV) and megavoltage (MV) x-ray beams in the development of such CBCT systems. In this paper, the inherent contrast and signal-to-noise ratio (SNR) performance for a variety of existing and hypothetical detectors for CBCT are investigated analytically as a function of imaging dose and object size. Theoretical predictions are compared to the results of experimental investigations employing largearea flat-panel imagers (FPIs) at kV and MV energies. Measurements were performed on two different FPI-based CBCT systems: a bench-top prototype incorporating an FPI and kV x-ray source (100 kVp x rays), and a system incorporating an FPI mounted on the gantry of a medical linear accelerator (6 MV x rays). The SNR in volume reconstructions was measured as a function of dose and found to agree reasonably with theoretical predictions. These results confirm the theoretically predicted advantages of employing kV energy x rays in imaging soft-tissue structures found in the human body. While MV CBCT may provide a valuable means of correcting 3D setup errors and may offer an advantage in terms of simplicity of mechanical integration with a linear accelerator (e.g., implementation in place of a portal imager), kV CBCT offers significant performance advantages in terms of image contrast and SNR per unit dose for visualization of soft-tissue structures. The relatively poor SNR performance at MV energies is primarily a result of the low x-ray quantum efficiencies (approximately a few percent or less) that are currently achieved with FPIs at high energies. Furthermore, kV CBCT with an FPI offers the potential of combined volumetric and radiographic/fluoroscopic imaging using the same device.
authors.affiliation: Deutsches Krebsforschungszentrum, Abteilung Medizinische Physik, Heidelberg, Germany.
authors.forename: B A
authors.initials: BA
authors.lastname: Groh
authors.forename: J H
authors.initials: JH
authors.lastname: Siewerdsen
authors.forename: D G
authors.initials: DG
authors.lastname: Drake
authors.forename: J W
authors.initials: JW
authors.lastname: Wong
authors.forename: D A
authors.initials: DA
authors.lastname: Jaffray
mesh_terms: D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011874:Radiometry; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*; D014965:X-Rays