Panoramic Imaging Of Gamma Knife Perfexion: From Geometric Validation Of Source Configuration To Source Calibration

Young-Bin Cho1, Monique Van Prooijen2, Nazanin Nayebi1, David Jaffray1, Mohammad Islam1

1Princess Margaret Hospital, Toronto, Canada 2Toronto, Canada

Keywords: physics, calibration, gamma knife, Imaging, dosimetry

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     To calibrate the dose rate of the Gamma Knife® (GK) PerfexionTM (PFX) at the time of source-collimator configuration verification using a panoramic imaging (PI) technique.
     A panoramic view of Cobalt sources was acquired by exposing a radio-chromic film wrapped around the surface of a cylindrical phantom. The centre of the phantom was mounted at the isocentre with its axis aligned along the longitudinal axis of the unit. Three sets of film were exposed to 100Gy at the isocentre for each collimator (4 mm, 8 mm, and 16 mm) at GK PFX. The sizes and shapes of the Cobalt source images were measured and compared with calculation for verification of the source-collimator configuration. The planning system was used to correlate the non-isocentric dose on film with the dose rate of the unit at the isocentre. The dose rate at the isocentre with 16 mm collimators was measured using the standard method with a PR-05P ion chamber and the manufacturer’s spherical dosimetry phantom. The dose rate with 8 mm and 4 mm collimators were determined using the published output factors.
     PI allowed clear identification of each source, verifying their integrity and selected collimator sizes. The dose rate of the unit using PI dosimetry agreed with the standard method within 2.4% (standard deviation of 2.0%), 3.4% (SD of 1.5%) and 1.0% (SD of 5.1%) for 4 mm, 8 mm, and 16 mm collimators respectively.
     The PI technique can be used as a secondary check of the dose rate calibration as well as for the verification of source-collimator configuration.
     It can be used as a comprehensive commissioning and routine quality assurance tool for the Gamma Knife systems.


Project Roles:

Y. Cho (), M. Van Prooijen (), N. Nayebi (), D. Jaffray (), M. Islam ()