Half of all cancer patients in the United States require radiation to combat their tumors. A form of radiation that uses protons, rather than X rays, to zap tumors causes fewer side effects to healthy tissue and may prove more effective.

Although these benefits of proton therapy have been known since the 1960s, it has yet to come into wide use. A key drawback: cost. Only a handful of hospitals can afford the equipment required to create high-energy proton beams.

Now a startup based in Littleton, MA, Still River Systems, is working with MIT physicists to develop a smaller, less expensive proton accelerator in the hopes of making the therapy more widely available. It expects the machine, which relies on advances in magnet technology to energize protons enough so they are therapeutic, to be in hospital trials in 2008.

During traditional radiation therapy, a clinician aims X-ray beams at a patient’s tumor. The X rays damage DNA and other molecules in the cancer cells–and in healthy cells–in the beam’s path. Proton beams can be focused far more sharply. “You can more precisely shape the [proton] dose to the shape and thickness of the tumor,” says Timothy Antaya, a technical supervisor at MIT’s Plasma Science and Fusion Center, who is working with Still River Systems. As a result, less surrounding healthy tissue is damaged during proton therapy.

But giving protons high enough energy to penetrate through the body to a tumor usually requires a large, expensive accelerator that must be housed in a different room than the patient. In order to penetrate 20 centimeters of water (the gold standard for these treatments), accelerators must rev up protons to 250 million electron volts. The equipment needed to generate such high-energy proton beams costs $100-200 million. Furthermore, in staffing, Antaya says, “For protons you need something like a small nuclear physics laboratory.”

Antaya says the machine from Still River Systems will be small enough to fit into the same room as the patient. “We’re taking advantage of advanced magnet technology,” he says. The company is using an accelerator known as a synchrocyclotron. Antaya says the new machines will be an order of magnitude smaller and an order of magnitude less expensive than current ones. And he says one of the group’s goals is to give the system a simple interface so that it doesn’t require a large, highly-trained staff.

Currently, only four hospitals in the United State have proton beam facilities, in Massachusetts, Indiana, California, and Texas (ones in Florida and Pennsylvania are under development). “If protons become more available, a lot of patients could benefit,” says Jay Loeffler, chief of radiation oncology at Massachusetts General Hospital in Boston, which has operated a proton beam since 2001. The hospital currently gives proton therapy to 60 patients a day.

Because proton beam therapy has not been in wide use, it is not clear which patients it could benefit the most. Clinicians know that the biggest benefits come in patients whose cancer has not yet spread beyond its initial site, and that children almost always benefit, says Loeffler. Protons generally work as well as, or better than, X rays, and with fewer side effects, he explains. Ongoing clinical trials will help clarify which patients benefit the most from the therapy. Loeffler says patients whose cancer has been discovered in its early stages are currently chosen for proton treatment.

Loeffler cautions that because Still River Systems has been secretive about its technology, its new approach hasn’t been evaluated by outside experts. Having a proton facility the same size as an X-ray facility is attractive, he says; but for the proton accelerator to be in the same room as the patient it must be proved safe–cyclotrons can give off stray radiation, as well as using tremendous voltage and power.

Antaya says that his group has taken safety into account from the beginning and that the design includes “sophisticated shielding and control of the surrounding environment.” Many hospitals have expressed interest in Still River Systems’ proton therapy, he adds.