COMPUTER-ASSISTED POSITIONING OF RADIOTHERAPY PATIENTS USING IMPLANTED RADIOPAQUE FIDUCIALS

For certain external beam radiotherapy procedures, precise alignment o f patients with the treatment beam is essential for good treatment out come. A method has been developed for quickly achieving precise Patien t alignment with the aid of stereoscopically located fiducial markers. The alignment algorithm is developed from standard rigid body mechani cs using closed form solutions, obviating the need for iterative fitti ng methods. The technique is implemented with a digitizing tablet and plane film radiographs. The accuracy of alignment with this method in phantom studies is better than 1 mm and 1 deg relative to CT data. The repeatability of positioning is 0.5 mm (standard deviation) and 0.36 deg (standard deviation).