by Charlie Osolin
Next-generation radiation therapy at a cancer clinic near you. That's the goal of an ambitious partnership between
Lawrence Livermore National Laboratory (LLNL) and the UC Davis Cancer Center — one of more than two dozen joint research projects involving the two institutions that promise breakthroughs in the detection, treatment and prevention of cancer.
LLNL and UC Davis have committed more than $3 million to develop a compact, relatively inexpensive proton-beam therapy system that can effectively zap tumors with powerful, focused radiation, while causing minimum collateral damage to nearby healthy tissue and organs.
An outgrowth of LLNL's weapons research, the technology is being developed by an LLNL team led by George Caporaso of LLNL's Physics and Advanced Technologies Directorate. LLNL is currently seeking commercial partners to help construct a compact proton-beam therapy system that could be clinically tested at the UC Davis Cancer Center.
Proton-beam therapy, available in hospitals only since 1990, is expected to become the "next big thing" in radiation treatment for many localized cancers, including those of the head and neck, eye and orbit, prostate, abdomen and lung.
Traditional x-ray and gamma ray therapy can damage the tissue the radiation passes through on the way to a target, limiting the amount that can be delivered to a deep-seated tumor. Protons, however, because of their positive charge and high mass, retain most of their energy until they reach the cancer site. Using sophisticated software algorithms, radiation oncologists can control the penetration depth and shape of the protons in three dimensions, fitting the radiation dose precisely to the shape of the tumor. This allows them to focus more potent doses on the cancer cells without endangering surrounding healthy cells.
Conventional proton therapy systems, however, are large — occupying as much space as a basketball court — and cost as much as $150 to $200 million to build, Caporaso said. "They have to be surrounded by concrete walls to protect against the radiation they generate," he added.
Because of their size and cost, there are only a few proton therapy centers in the United States and only about 20 in the world. Several more are under construction or being planned, but availability of the treatment will remain limited for some time.
On the other hand, if the huge accelerators could be made compact enough to fit in a single room — a significant technical challenge — and built for less than one-tenth the cost, the therapy could be offered in radiation oncology clinics across the country.
That's where the LLNL-UC Davis Cancer Center partnership comes in.
One of the first projects the two institutions launched after they agreed to collaborate in 2000, the compact proton accelerator would use an LLNL-developed technology called the dielectric wall accelerator (DWA), which enables protons to be accelerated to the required energies — as much as 100 million electron volts per meter — without using bending magnets or other techniques that take up space and generate unwanted radiation.
The dielectric wall uses a high-voltage-gradient insulator to handle high electricfield stresses, enabling a proton therapy accelerator to successfully operate without being short-circuited.
Today's hospital proton radiotherapy machines generate from 70 million volts for eye tumors to 250 million volts for tumors deep in the body. A dielectric wall only 2.5 meters long could withstand the 250 million volts required to treat deep-seated tumors. The LLNL researchers have successfully tested a small (3-millimeter-long) dielectric wall sample that withstood an electric field of 100 million volts per meter.
Caporaso said the idea of using the DWA technology for cancer treatment "really started moving when Dennis Matthews (director of LLNL's Center for Biotechnology, Biophysical Sciences, and Bioengineering) approached me with the vision that if you could make (a proton accelerator) really, really small, it might be able to go into existing x-ray therapy clinics in place of conventional x-ray machines.
"We had been developing the accelerator for a long time for radiography and other defense applications, but Dennis helped us put together an LDRD (Laboratory-Directed Research and Development) proposal that was approved for funding," Caporaso said. He noted that Ralph DeVere White, director of the UC Davis Cancer Center, "has been a rock-solid, enthusiastic supporter" of the project. "His support has been key to our progress so far."
The project's initial funding, which ended last September, enabled the team to push the system's components to 50 percent of their performance targets. Additional funds from LLNL and UC Davis will "allow us to work toward a subscale (20-centimeter-long) prototype — a kind of a proof of principle device," Caporaso said. "We think we can build enough of the accelerator to demonstrate the operating principles and characteristics within the next 18 months.
"There are a lot of technical challenges remaining," he said. "We'll see if we can push the components to 100 percent over the next year, but we can't test the remaining issues until we build the prototype.
"So it remains to be seen if we can pull it off," Caporaso said. "There are no guarantees, but progress has been good so far and we're optimistic."
