Infrared light offers promise of laser-sharp cancer therapy

Claiming scalpel-like precision, Canadian scientists have delivered lightning-fast laser pulses of infrared light to obliterate tumors in animals. Whereas conventional radiation therapy delivers cell-killing radiation to all cells throughout a beam’s path, the new approach causes no damage to tissue surrounding a targeted tumor, its creators say.

The spillover damage to healthy bystander cells triggers the nausea and other side effects associated with conventional radiation therapy, explains Nancy Ellerbroek, a clinical radiation oncologist in Manhattan Beach, Calif. So, if the new technology can treat tumors deep inside the body without exposing healthy tissue, “that would be really great,” she says.

The just-patented system under development at the University of Sherbrooke in Canada delivers 1,000 pulses of infrared light per second, each lasting only about 100 quadrillionths of a second, explains laser physicist and study coauthor Daniel Houde. In tiny regions of tissue — typically a volume about 100 micrometers in diameter and up to 10 centimeters long — this blast briefly creates a low-energy electron plasma called a filament, in which molecules are stripped of their outer electrons.

To illustrate the laser’s accuracy, Houde’s team irradiated a clear gel that turns cloudy when exposed to enough radiation to kill human cells. Using laser pulses, the Sherbrooke scientists wrote the S from their university’s logo into the gel. No gel in front of the S turned cloudy, the researchers report online August 27 in the Proceedings of the National Academy of Sciences. When the researchers repeated the experiment with a gamma radiation beam, all gel in the path of the beam turned cloudy, up to and including the targeted region.

Functionally, the laser’s impact on affected tissue is exactly like X-rays, Houde says. Both types of radiation unleash electrons that deposit lethal amounts of energy. Both also induce the production of free radicals, molecular fragments that kill cells.

The laser therapy obliterated tumors induced experimentally in mice. However, those tumors were just under the skin of the animals’ legs. Still unclear, Houde acknowledges, is how deeply filaments can be induced and still maintain their pinpoint accuracy. The goal, he says, “is to begin tests in humans within two years.”

Radiation oncologist Theodore Phillips of the University of California, San Francisco, suspects the laser technique may have limited applicability given the questions about how deeply inside the body it will work. “I suspect perhaps 1 or 2 centimeters at best,” he says. So, for the more common, deeper tumors, he says, this technique would hold little appeal.

The researchers are already at work on a system to beam the laser’s pulses through a fiber-optic cable. Then surgeons could, for example, use the laser like a scalpel during surgery with no need for lead shielding or other types of radiation protection, Houde says.