A quality assurance procedure to evaluate cone-beam CT image center congruence with the radiation isocenter of a linear accelerator

This paper introduces a new quality assurance (QA) method for checking if the center of the images produced by a cone-beam CT (CBCT) scanner aligns with the radiation isocenter of a linear accelerator. Unlike older methods, this one doesn't require precise positioning of a ball bearing (BB) phantom using room lasers or light field crosshairs. The method uses a Winston-Lutz test to find the radiation isocenter relative to a stationary BB phantom, minimizing setup uncertainties and improving accuracy.

• 1
  The CBCT image center exhibits excellent short-term positional reproducibility, with less than 0.1 mm of wobble in each direction during consecutive acquisitions.
• 2
  Over a seven-month period, the CBCT image center deviated from the radiation isocenter by 0.40 ± 0.12 mm (x), 0.43 ± 0.04 mm (y), and 0.34 ± 0.14 mm (z).
• 3
  A clinical case study revealed a 0.8 mm discrepancy between the CBCT image center and the MV EPID image center in the anterior-posterior direction.