Abstract: A method and apparatus for verifying radiation beam alignment in an image guided stereotactic radiosurgery (SRS) delivery system such as the Cyberknife™. This invention achieves precise verification of radiation beam alignment with a radiation beam detection apparatus mounted on a gimbal assembly. The radiation beam detection apparatus houses an alignment fixture of varying geometric shape, such as a metallic ball or can be an array of radio-opaque markers positioned symmetrically at the gimbal assembly's common rotation center. The radiation detection apparatus comprises a radiation detector such as film and an alignment mirror, which are parallel to each other on opposite sides of the alignment fixture. The radiation detector is used to capture a radiographic image of the alignment fixture and the circular radiation field. The resulting image is analyzed to determine the eccentricity of the radiation field and whether adjustment of node positions is required to eliminate any eccentricity.

Abstract: A method and apparatus for quality assurance of beam geometry of robotic radiosurgery systems. The apparatus comprises two or more radio-opaque markers set at a fixed distance from each other and contained in a housing, which is assembled to a collimator fixture for attachment to the collimator interface of the LINAC of a robotic radiosurgery system. A treatment plan is generated to position the LINAC to a series of pre-defined radiation beam orientations, then a simulation of the treatment is carried out, and radiographic images are taken at each LINAC position. The coordinates of the radio-opaque markers obtained from the images are used to determine beam orientation by calculating their directional cosines, the beam off-axis error and the deviation of the radiation source to iso-center distance (SAD). The imaging system is independently calibrated and the quantitative beam geometric information is used to adjust beam geometry for quality assurance.

Abstract: A method for routine monitoring and quality assurance of field asymmetry of high energy circular radiation beam producing equipment. The quality assurance process of field symmetry for devices such as stereotactic radiosurgery (SRS) systems is simplified by directly measuring the integration of the half-beam profile. The method of the invention provides that the field symmetry is obtained by positioning the tip of an ion chamber, with a collecting length approximately half the diameter of the beam, at the central axis of the beam, and rotating the ion chamber at varying angular positions, acquiring and comparing readings at desired angular positions. Each pair of readings from positions 180 degrees opposed from each other, are plugged into the equation, Asymmetry=2(R1?R2)/(R1+R2) to compute asymmetry.