Two‐dimensional dose distribution of a miniature x‐ray device for stereotactic radiosurgery

The Photon Radiosurgery System is a miniature x‐ray device developed for the treatment of small intracranial neoplasms. The x rays are generated at the tip of a 10‐cm‐long, 3‐mm‐diam probe with a nearly isotropic distribution. Results from measurements of the two‐dimensional dose distribution around the x‐ray source are presented using two methods: (1) dose measurement with an ionization chamber and a water phantom system and (2) dose measurement with radiochromic film and a solid water phantom. The shape of the two angular dose distributions in the axial plane agree with each other to within approximately 10% and the dose at 10 mm from the source, orthogonal to the probe axis, was about 20% lower than at the same distance along the axis. The relative dose difference of 20% corresponds to a change in distance from the source of ± 0.3   mm at 10 mm. It is shown that the anisotropy of radiation distribution in the axial plane can be improved to approximately 10% by adjusting the electron beam with a 12% reduction in the overall radiation output.