Radiation Therapy Planning: an Uncommon Application of Lisp

We used Common Lisp to build a complex and powerful interactive graphics simulation system called \Prism", for planning radiation therapy. Special features of Common Lisp that we used to advantage include: lexical closures, the Common Lisp Object System (CLOS), and the Common Lisp binding to the X window system (CLX). We use events, indirect invocation and mediators to achieve modularity. Some of the components of Prism are: a contoured volume editor, computed medical images, a rule based function to generate target volumes, and a radiation dose computation function. To achieve fast oating point computation in the latter, we applied both generic and vendor speci c optimizations. The result is a system that is routinely used in the University of Washington Cancer Center, by people with no programming expertise. Our experience shows that Lisp is practical, powerful and e cient for interactive graphics, complex modeling and intensive oating point computations such as radiation dose modeling. Additional work in progress includes a medical image server and an interface to an on-line anatomy atlas.