THE USE OF MEDICAL IMAGES IN PLANNING AND DELIVERY OF RADIATION-THERAPY

The authors provide a survey of how images are used in radiation thera py to improve the precision of radiation therapy plans, and delivery o f radiation treatment. In contrast to diagnostic radiology, where the focus is on interpretation of the images to decide if disease is prese nt, radiation therapy quantifies the extent of the region to be treate d, and relates it to the proposed treatment using a quantitative model ing system called a radiation treatment planning (RTP) system. This ne cessitates several requirements of image display and manipulation in r adiation therapy that are not usually important in diagnosis. The imag es must have uniform spatial fidelity: i.e., the pixel size must be kn own and consistent throughout individual images, and between spatially related sets. The exact spatial relation of images in a set must be k nown. Radiation oncologists draw on images to define target volumes; d osimetrists use RTP systems to superimpose quantitative models of radi ation beams and radiation dose distributions on the images and on the sets of organ and target contours derived from them. While this mainly uses transverse cross-sectional images, projected images are also imp ortant, both those produced by the radiation treatment simulator and t he treatment machines, and so-called ''digital reconstructed radiograp hs,'' computed from spatially related sets of cross-sectional images. These requirements are not typically met by software produced for radi ologists but are addressed by RTP systems. This review briefly summari zes ongoing work on software development in this area at the Universit y of Washington Department of Radiation Oncology.