title: Low-dose megavoltage cone-beam computed tomography for lung tumors using a high-efficiency image receptor.
abstract: We report on the capabilities of a low-dose megavoltage cone-beam computed tomography (MV CBCT) system. The high-efficiency image receptor consists of a photodiode array coupled to a scintillator composed of individual CsI crystals. The CBCT system uses the 6 MV beam from a linear accelerator. A synchronization circuit allows us to limit the exposure to one beam pulse [0.028 monitor units (MU)] per projection image. 150-500 images (4.2-13.9 MU total) are collected during a one-minute scan and reconstructed using a filtered backprojection algorithm. Anthropomorphic and contrast phantoms are imaged and the contrast-to-noise ratio of the reconstruction is studied as a function of the number of projections and the error in the projection angles. The detector dose response is linear (R2 value 0.9989). A 2% electron density difference is discernible using 460 projection images and a total exposure of 13 MU (corresponding to a maximum absorbed dose of about 12 cGy in a patient). We present first patient images acquired with this system. Tumors in lung are clearly visible and skeletal anatomy is observed in sufficient detail to allow reproducible registration with the planning kV CT images. The MV CBCT system is shown to be capable of obtaining good quality three-dimensional reconstructions at relatively low dose and to be clinically usable for improving the accuracy of radiotherapy patient positioning.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Jussi
authors.initials: J
authors.lastname: Sillanpaa
authors.forename: Jenghwa
authors.initials: J
authors.lastname: Chang
authors.forename: Gikas
authors.initials: G
authors.lastname: Mageras
authors.forename: Ellen
authors.initials: E
authors.lastname: Yorke
authors.forename: Fernando
authors.initials: F
authors.lastname: De Arruda
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Rosenzweig
authors.forename: Peter
authors.initials: P
authors.lastname: Munro
authors.forename: Edward
authors.initials: E
authors.lastname: Seppi
authors.forename: John
authors.initials: J
authors.lastname: Pavkovich
authors.forename: Howard
authors.initials: H
authors.lastname: Amols
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D036542:Tomography, Spiral Computed / Q000295:instrumentation* / Q000379:methods; D014159:Transducers