Three-dimensional compensating filters using magnetic resonance images

A technique for making radiation therapy compensators for missing tissue using magnetic resonance imaging (MRI) is presented. Magnetic resonance imaging was chosen for its ability to provide easily visible, accurate patient contours at any treatment angle. Phantom studies, including coronal cuts of a 45-degree phantom, showed that distortion in the magnetic resonance imaging is minimal, but that the image magnification should be checked by placing markers on the patient during the procedure. Water bath studies of 4 MV radiation dose uniformity in a compensated 45-degree phantom exhibited variations of less than 4% from the open beam profile. Errors in constructing and using compensators with this technique are analyzed and simulated.