title: Integration of optical imaging with a small animal irradiator.
abstract: OBJECTIVE
  The authors describe the integration of optical imaging with a targeted small animal irradiator device, focusing on design, instrumentation, 2D to 3D image registration, 2D targeting, and the accuracy of recovering and mapping the optical signal to a 3D surface generated from the cone-beam computed tomography (CBCT) imaging. The integration of optical imaging will improve targeting of the radiation treatment and offer longitudinal tracking of tumor response of small animal models treated using the system.
  
  
  METHODS
  The existing image-guided small animal irradiator consists of a variable kilovolt (peak) x-ray tube mounted opposite an aSi flat panel detector, both mounted on a c-arm gantry. The tube is used for both CBCT imaging and targeted irradiation. The optical component employs a CCD camera perpendicular to the x-ray treatment/imaging axis with a computer controlled filter for spectral decomposition. Multiple optical images can be acquired at any angle as the gantry rotates. The optical to CBCT registration, which uses a standard pinhole camera model, was modeled and tested using phantoms with markers visible in both optical and CBCT images. Optically guided 2D targeting in the anterior/posterior direction was tested on an anthropomorphic mouse phantom with embedded light sources. The accuracy of the mapping of optical signal to the CBCT surface was tested using the same mouse phantom. A surface mesh of the phantom was generated based on the CBCT image and optical intensities projected onto the surface. The measured surface intensity was compared to calculated surface for a point source at the actual source position. The point-source position was also optimized to provide the closest match between measured and calculated intensities, and the distance between the optimized and actual source positions was then calculated. This process was repeated for multiple wavelengths and sources.
  
  
  RESULTS
  The optical to CBCT registration error was 0.8 mm. Two-dimensional targeting of a light source in the mouse phantom based on optical imaging along the anterior/posterior direction was accurate to 0.55 mm. The mean square residual error in the normalized measured projected surface intensities versus the calculated normalized intensities ranged between 0.0016 and 0.006. Optimizing the position reduced this error from 0.00016 to 0.0004 with distances ranging between 0.7 and 1 mm between the actual and calculated position source positions.
  
  
  CONCLUSIONS
  The integration of optical imaging on an existing small animal irradiation platform has been accomplished. A targeting accuracy of 1 mm can be achieved in rigid, homogeneous phantoms. The combination of optical imaging with a CBCT image-guided small animal irradiator offers the potential to deliver functionally targeted dose distributions, as well as monitor spatial and temporal functional changes that occur with radiation therapy.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada and Techna Institute, University Health Network, 124-100 College Street, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Weersink
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada.
authors.forename: Steve
authors.initials: S
authors.lastname: Ansell
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada.
authors.forename: An
authors.initials: A
authors.lastname: Wang
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada.
authors.forename: Graham
authors.initials: G
authors.lastname: Wilson
authors.affiliation: Techna Institute, University Health Network, 124-100 College Street, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Duoaud
authors.initials: D
authors.lastname: Shah
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5S 1A1, Canada.
authors.forename: Patricia E
authors.initials: PE
authors.lastname: Lindsay
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada; Techna Institute, University Health Network, 124-100 College Street, Toronto, Ontario M5G 1P5, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5S 1A1, Canada; Ontario Cancer Institute, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada; and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5S 1A1, Canada.
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
mesh_terms: D000465:Algorithms; D000818:Animals; D002138:Calibration; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D021621:Imaging, Three-Dimensional / Q000379:methods; D051379:Mice; D008954:Models, Biological; D009374:Neoplasms, Experimental / Q000473:pathology; D061848:Optical Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D055618:Radiation Equipment and Supplies; D014965:X-Rays