A FRAMELESS METHOD FOR STEREOTAXIC RADIOTHERAPY

A frameless method for stereotactic multiple are radiotherapy (SMART) is described. Three short gold wires are implanted in the scalp approx imately 100 mm apart. These are localized in a computed tomographic or angiographic study along with the target. Subsequently the gold marke rs are localized on beam films and the target position calculated usin g a computer program ISOLOC. This program provides the couch movements required to move the target to the isocentre and a micropositioner at tached to the couch is used to make the adjustment. Beam films are rep eated until the movements required are less than 1 mm in any direction . It is shown that the simple procedures of implanting the markers sub cutaneously do not provide a stable reference system in about 25% of p atients and the markers are now screwed into the cranium. The precisio n of the method is evaluated by phantom studies and measurements taken during several hundred treatments.