: The Gamma Knife is a stereotactic radiation surgery machine which focuses about 200 cobalt-60 gamma-ray beams on a therapeutic target.  Its accuracy control and management of irradiation are at present performed using X-ray films. This method is, however, insufficient to provide sufficient accuracies in space distributions of the beams as well as dose distributions.  Furthermore, computed radiography systems widely used in modern clinical settings add to the difficulty in evaluating accuracy management of radiation therapy machines.

     We investigated whether using imaging plate (IP) is a practical approach to accuracy management of the Gamma Knife.

      

     We positioned an IP parallel to the front face of its collimator helmet and irradiated it by gamma-ray beams from about 200 cobalt-60 sources for 0.1 minute. We could observe each beam clearly on the IP. We repeated the procedure at different axial positions (3mm – 15mm) of IP from the front face of the collimator. Images obtained by this method enabled us to evaluate beam profiles from the cobalt sources from the Gamma Knife.

     This indicated a possibility of evaluating 50% isodose region at the center of the irradiation field.  From these measurements we demonstrated the feasibility of an accurate evaluation of isodose distribution at the center of the irradiation field.

     This is a retrospective study.

     In conclusion, this study showed that we could establish a simple, convenient and practical method to check the center of irradiation filed.

     Also, we established a useful method for the accuracy management of the Gamma Knife by using the imaging plate.