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Targeting Cancer

Early clinical trials of the use of heavy-ion radiation as a cancer treatment have shown promise. An experimental facility near Tokyo uses technology originally developed for the study of nuclear physics to blast inoperable cancer tumors with beams of carbon ions.


CHIBA, Japan — The before-and-after CAT scans are dramatic: The first shows a tumor lodged deep in the patient's head, his right eye protruding from the pressure. The second shows a return to normal.

The patient was one of the first to be treated in clinical trials here at the world's only heavy-ion accelerator built specifically for cancer therapy--an enormous high-tech apparatus several basketball courts long that can zap tumors with carefully targeted beams of particles.

Three years after his treatment, the 77-year-old man "is still alive, and there's no problem," said Hirohiko Tsuji, director of radiation medicine at Japan's National Institute of Radiological Sciences, which runs the unique facility in this Tokyo suburb.

Clinical trials on a limited

number of patients with inoperable cancers started in 1994 at the experimental center, called the Heavy-Ion Medical Accelerator in Chiba, or HIMAC.

Testing so far is focused on toxicity studies, not comparative cure rates. Initial results on the first 145 patients indicate the treatment is generally safe at the doses used so far and that it is effective for some types of cancers, Tsuji said.

HIMAC works by stripping off the negatively charged electrons from carbon atoms, accelerating the atoms' positively charged nuclei--the atoms' cores--to 65% of the speed of light, then shooting them into tumors where they so disrupt molecular structures that cancer cells die.

The key advantage of this treatment is that the destructive power of the heavy-ion beam can be delivered almost entirely to the tumor itself, thus avoiding damage to surrounding tissue.

Tumors were destroyed, with no signs of regrowth six months after treatment, in 123 out of the 145 patients treated from June 1994 to August 1996, according to institute statistics. Among the first 43 patients, 29 showed no signs of recurrence 18 months after treatment.

These statistics look only at the specific tumors that were treated, and in some patients the cancers had already spread, so the figures are not cure rates. One of the weak points of heavy-ion therapy is that it is of little use in cases where cancer has already metastasized.

"We do not think it is a miracle bullet," Tsuji stressed. "It has advantages and disadvantages."

The technology builds on work started at the Lawrence Berkeley Laboratory in Berkeley, where from 1977 to 1992, researchers treated about 1,300 patients with an accelerator built in 1954.

The Berkeley machine had produced many ground-breaking discoveries in nuclear physics--and four Nobel prizes--before being turned to cancer research. It was shut down in a 1992 cost-cutting move by the Energy Department, to save about $15 million a year.

The work at Berkeley, which used less sophisticated equipment than that at HIMAC, indicated that heavy-ion cancer therapy held promise for treatment of some kinds of inoperable tumors. The decision to build HIMAC was based partly on the Berkeley results.

After it opened in 1994, HIMAC was the only facility in the world offering heavy-ion therapy. An existing heavy-ion research center in Darmstadt, Germany, is also gearing up to treat cancer patients.

Most U.S. researchers have felt that although the work at Lawrence Berkeley was interesting, the enormous expense of building heavy-ion accelerators to treat cancer couldn't be justified when compared with alternative uses.

Much less expensive--but perhaps less effective--proton accelerators are in use at a few centers in the United States, mainly Loma Linda Medical Center and Massachusetts General Hospital in Boston. These work according to similar principles as HIMAC but use smaller particles--protons--that pack less punch.

Conventional radiation therapy for cancer uses X-rays or gamma rays, which are forms of electromagnetic radiation that have no mass. Their destructive energy cannot be focused as directly as is possible with particle beams. That means X-ray or gamma ray doses powerful enough to kill a tumor may also have severe side effects.

There is little doubt that in terms of physics and biology, heavy ions are better than protons for killing cancer tumors, said Joseph R. Castro, professor of radiation oncology at UC San Francisco's School of Medicine, who headed the studies at Lawrence Berkeley.

"The research question is, 'Is it worth the extra money?' " Castro said. "I think it's premature to make any judgment about how valuable heavy-ion treatment will be. . . . If the Japanese or the Germans were to show over the next five years that this could make a major impact on one or more tumor sites, then I think you would see some consideration of getting this started in the U.S. again."

Despite the potential advantages, a facility such as HIMAC is so expensive that even in Japan it probably would never have been built if its funding had had to come from the nation's medical or cancer research establishment.

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