Radiation facilities

Radiation facilities at the Norris Cotton Cancer Center include a Cobalt 60 unit, a linear accelerator, and a 45-million-electron-volt betatron (one of only six in the country). Therapy with these units has recently been raised to a fine art through the acquisition of two new auxilliary machines the latest "cat" scanner and a stateof-the-art treatment-planning computer.

Computerized axial tomography ("cat") scanners use computers to build x-ray "slices" of the body into highly accurate, highly individualized pictures, providing noninvasively a direct view of any cross section of the body desired. The new scanner at Norris Cotton is a high-speed machine, explains Peter Spiegel, director of diagnostic radiology at the center: "Because its images are more detailed and because scans can be done in five seconds as opposed to two and a half minutes which is how long-the previous scanner took we can see parts of the body that used to be blurred by respiratory motion. No one can hold his or her breath for two and a half minutes, but nearly everyone even very sick patients and children can hold the breath for five seconds."

It is these increasingly clear and accurate images of individual tumors that have revolutionized radiation therapy brought it from a shot in the dark to a sophisticated therapeutic tool, largely through the marriage of the scanner with the treatment-planning computer. Such a computer, working with images provided by the scanner, allows radiation therapists to test radiation dosages on a video-screen. They can deliver various hypothetical doses to the imaged tumor and find out through the machine's instant replay just where and at what stength the "fallout" of the dose will be. Thus, by rapid experimentation, physicists and dosimetrists can determine the best strength and type of radiation to be trained on a tumor from the best angle to achieve optimal radiation with the least amount of damage to surrounding healthy tissue. (To see what dosimetrist Frank Conine, shown below at the treatment planner, works with, have a look at this month's cover.) "Twenty years ago," says Assistant Professor Alexander Filimonov of the Radiation Therapy Department, "we had to do these computations by hand, in only two dimensions, and it took hours to do a fraction of what we can now do in two minutes or less."