Determining locations of intracerebral lesions for proton radiotherapy.

Using an external view of the head, the ability to direct a proton radiotherapy beam at an intracerebral lesion is described, using a biostereometric (BSM) technique. The positions of markers, recognizable on computed tomography (CT) or magnetic resonance (MR) images, at known locations on the skin of a patient's head are related to the site of the lesion seen on the images. The markers' positions are determined by a BSM device, incorporating six video cameras coupled to a computer. A transformation from a coordinate system, defined by the CT or MR images, to another coordinate system, that of the BSM device, allows the proton beam to be directed towards the lesion. Markers used in this work were solid steel spheres for CT and plastic spheres containing oil for MR images.