A feasibility study using a stereo-optical camera system to verify Gamma Knife treatment specifications

The Gamma Knife, Model B, treatment unit has no independent record and verify system, but requires human intervention to double-check critical treatment settings prior to irradiation of a patient. One may double-check approximately 50 settings for an average treatment. Human errors made when adjusting and verifying the Leksell stereotactic frame settings and/or failure to select the correct collimator helmet could result in a misadministration. As a safeguard, a stereo-optic camera system was employed to independently measure most of the critical Gamma Knife settings prior to irradiation. Those that are monitored and recorded by the system include: Leksell stereotactic frame x,y, and z coordinates, γ angle, and the treatment collimator aperture. The irradiation time setting could not be monitored prior to irradiation and remains to be double-checked by the operator. The treatment verification hardware consists of a computer workstation that is connected to a stereo-optic camera system, which consists of a wand having light emitting diodes (LEDs) embedded in the handle. The positions of the LEDs are recorded by the camera system to locate the pointed tip of the wand. Prior to irradiation, the camera system is directed toward the head of the patient in treatment position. The wand tip is touched to a set of known locations on the Leksell frame and the collimator helmet. The position of the stereotactic frame relative to the collimator helmet can then be determined and its treatment settings calculated. Our results show agreement within 1mm in any axis.