X-rays Target Brain Tumors, Spare Healthy Tissue

Bjorn Carey

Date: 05 June 2006 Time: 01:03 PM ET

Scientists have developed a method for treating brain and spinal cord tumors in rats that delivers radiation to a cancerous growth while doing little or no damage to surrounding healthy tissues.

Current methods for killing cancerous tumors include bombarding the bad tissues with chemicals (chemotherapy) or radiation (radiation therapy). In some cases doctors decide to perform surgery to physically remove the cancerous growth.

While in some cases effective, these treatments can have serious drawbacks when used in the brain and central nervous system. If the treatment is too aggressive, the patient will likely lose some ability to function. However, if treatment's not aggressive enough, there's a good chance the cancer will return.

Segmented attack

The new technique involves using an X-ray beam, except instead of hitting the tumor with a solid beam, this one is split into several parallel beams less than a millimeter thin.

It's like changing the setting on a hose nozzle from "stream" to "shower."

Using rats with brain and spinal cord tumors, the researchers first showed that the segmented beam could pass through normal tissue without permanently damaging it. After seven months the rats showed no or little damage to the nervous system.

"The normal brain tolerates these beams much better than complete beams because tissue survives between the thin beams," said study co-author Avraham Dilmanian of Brookhaven National Laboratory. "The undamaged cells that are in capillary blood vessels help repair the lost segments."

'X' marks the spot

By aiming two segmented beams angled 90 degrees apart at the tumor, this technique can produce a beam that delivers an intense X-ray dose at the target—like a collision of two cars at an intersection—but not the surrounding tissue.

"When the two arrays reach each other at the target, they went between each other and interlaced," Dilmanian told LiveScience. "Because we chose the spacing between the rays, we produced a complete beam on the target."

Scans of the rats' tissues revealed no damage beyond the target range after exposing the rats to the two-beam approach for six months.

Scientists can't say for sure how this method kills a tumor, though.

Dilmanian offers one possibility: As the tumor grows, it grows its own blood vessels. The X-rays damage these vessels, which cuts off the tumor's food supply and causes it to die.

"What we think is happening is that the tumor's blood vessels don't know how to repair themselves from this damage that normal tissue would recover from," Dilmanian said.

Lacking energy?

The new method is an improvement on an earlier study that used even thinner X-rays. But those ultra-thin beams can only be produced by machines called synchrotrons, devices that few laboratories can afford. By using thicker beams, the new method can be tested by more labs and perhaps someday be used in hospitals for routine treatments.

Questions remain about how effective the process will be, however.

X-rays lose their intensity as they pass through tissue, and the low-energy beams used in the study fall off even more sharply, Dilmanian said. It remains to be seen how effectively these beams will penetrate human tissue.

"It depends on the depth and size of the tumor," Dilmanian said. "It might be difficult to treat deep tumors. We think we can handle brain tumors of medium size in that regard."

Scientists might have to wait for the manufacturers of X-ray tubes—which generate X-ray radiation—to produce tubes capable of producing segmented beams at higher energies than currently available.

The work, funded in part by the National Institutes of Health and the U.S. Department of Energy, is detailed in the June 5 online edition of the journal Proceedings of the National Academy of Sciences.