University of Wisconsin-Madison Physical Sciences Lab

Learn More: Tomotherapy

[Tomotherapy Drawing] PSL teamed up with Thomas "Rock" Mackie of the UW-Madison Department of Medical Physics and Human Oncology to develop a prototype tomotherapy device for radiation therapy to treat cancer. Tomotherapy, literally "slice" therapy, is a new form of cancer radiation therapy that combines the precision of a CT (computerized tomography) scan with the potency of radiation treatment to selectively destroy cancerous tumors while minimizing damage to surrounding tissue.

Unlike traditional radiation therapy systems which have beams projecting onto the tumor from a few different directions, tomotherapy rotates the beam source around the patient, thus allowing the beam to enter the patient from many different angles in succession. The advantage is that instead of having, for example, six beams, each with 1/6 the dosage necessary to irradiate the tumor, the tomotherapy beam has only 1/72 the dosage and is projected into the tumor from 72 different positions as it rotates. Thus the tumor is more precisely targeted and the healthy tissue surrounding the tumor is subjected to much lower dosages of radiation.

The intensity of the beam is modulated through the use of a multi-leaf collimator system, thus further improving the precision of the treatment. By moving the radiation-blocking leaves in and out of the beam path with speed and precision, the location and intensity of the radiation entering the patient is accurately controlled. Also aiding in the precision targeting offered by tomotherapy is the inclusion of CT imaging technology within the tomotherapy device itself. This allows technicians to precisely locate the tumor before and during treatment.

The tomotherapy device under development by Mackie and his group is the first to integrate and automate the entire process of radiotherapy from precision location to treatment. Also, unlike other precision radiotherapy devices being tested, the patient is continuously moved through the device while the beam source rotates thus creating a spiral scan pattern. This continuous helical delivery pattern is faster, more accurate and avoids "seams" between scan slices that can occur with some other methods.

PSL was involved in the design and construction of the tomotherapy prototype beginning in July of 1995. The first unit was completed at PSL and shipped in February 2001 to the University of Wisconsin Comprehensive Cancer Center. PSL fabricated some parts of the multi-leaf collimator for an additional 3 units. Here is an mpg video file (1.4MB, 15 seconds play time) of the prototype under test at PSL, and an mpg video file (1.4MB, 15 seconds play time) of the multi-leaf collimator.

Tomotherapy Inc. was established to commercialize this improved radiotherapy approach. Its success is shown by the existence of over 100 installed systems worldwide, continued expansion, and a successful initial stock offering.

Visit the UW Medical Physics website or the Tomotherapy Inc. website.