A radiation therapy apparatus includes a collimator that changes the width of a fan beam of radiation as a treatment volume of the patient crosses the volume exposed by the beam so as to minimize the irradiation of healthy tissue at the front and back of the tumor. The width of the fan beam may also...http://www.google.ca/patents/US5442675?utm_source=gb-gplus-sharePatent US5442675 - Dynamic collimator for radiation therapy
