title: A moving blocker-based strategy for simultaneous megavoltage and kilovoltage scatter correction in cone-beam computed tomography image acquired during volumetric modulated arc therapy.
abstract: OBJECTIVE
  To evaluate a moving blocker-based approach in estimating and correcting megavoltage (MV) and kilovoltage (kV) scatter contamination in kV cone-beam computed tomography (CBCT) acquired during volumetric modulated arc therapy (VMAT).
  
  
  METHODS
  During the concurrent CBCT/VMAT acquisition, a physical attenuator (i.e., "blocker") consisting of equally spaced lead strips was mounted and moved constantly between the CBCT source and patient. Both kV and MV scatter signals were estimated from the blocked region of the imaging panel, and interpolated into the unblocked region. A scatter corrected CBCT was then reconstructed from the unblocked projections after scatter subtraction using an iterative image reconstruction algorithm based on constraint optimization. Experimental studies were performed on a Catphan® phantom and an anthropomorphic pelvis phantom to demonstrate the feasibility of using a moving blocker for kV-MV scatter correction.
  
  
  RESULTS
  Scatter induced cupping artifacts were substantially reduced in the moving blocker corrected CBCT images. Quantitatively, the root mean square error of Hounsfield units (HU) in seven density inserts of the Catphan phantom was reduced from 395 to 40.
  
  
  CONCLUSIONS
  The proposed moving blocker strategy greatly improves the image quality of CBCT acquired with concurrent VMAT by reducing the kV-MV scatter induced HU inaccuracy and cupping artifacts.
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, United States.
authors.forename: Luo
authors.initials: L
authors.lastname: Ouyang
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, United States.
authors.forename: Huichen Pam
authors.initials: HP
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, United States. Electronic address: jing.wang@UTsouthwestern.edu.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D010388:Pelvis / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
keywords: CBCT; Hounsfield unit accuracy; Megavoltage scatter correction; Moving blocker; VMAT