Proton therapy is considered the most advanced form of radiation therapy available, but, until recently, size and cost have limited the technology's use to only six cancer centers nationwide. That is about to change, as the first compact proton therapy system for use in a clinical setting entered development in June.

The result of defense-related research, the compact system was originally developed by scientists at Lawrence Livermore National Laboratory. The project was jointly funded by the laboratory and UC Davis Cancer Center, and the technology has been licensed to TomoTherapy Inc.

TomoTherapy will fund development of the first clinical prototype, which will be tested on patients at UC Davis Cancer Center. If clinical testing is successful, TomoTherapy will bring the machines to market. The compact system will be designed to fit into any major cancer center and will cost a fifth as much as a full-scale machine.

"We have taken proton therapy and achieved major advances toward what we were told was impossible – to scale it down to a size and price that will bring it in reach of every major cancer center," said Ralph deVere White, director of the UC Davis Cancer Center and associate dean for cancer programs.

Conventional radiation therapy kills cancer cells using high-energy X-rays that deliver energy to all the tissues they travel through, from the point they enter the body until they leave it. Doctors therefore must limit the dose delivered to the tumor in order to minimize damage to surrounding healthy tissue. In contrast, proton beams deposit almost all of their energy on their target, with a low amount of radiation deposited in surrounding tissues. This enables doctors to hit tumors with higher, potentially more effective radiation doses.