2-DIMENSIONAL DOSE DISTRIBUTION OF A MINIATURE X-RAY DEVICE FOR STEREOTACTIC RADIOSURGERY

The Photon Radiosurgery System is a miniature x-ray device developed f or the treatment of small intracranial neoplasms. The x rays are gener ated at the tip of a 10-cm-long, 3-mm-diam probe with a nearly isotrop ic 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 s ystem and (2) dose measurement with radiochromic film and a solid wate r phantom. The shape of the two angular dose distributions in the axia l 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 dif ference 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 dist ribution in the axial plane can be improved to approximately 10% by ad justing the electron beam with a 12% reduction in the overall radiatio n output. (C) 1998 American Association of Physicists in Medicine.