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  • Two-Photon Therapy Holds Promise as Cancer Treatment

Photonics Spectra
Jan 1997
Kathleen G. Tatterson

OAK RIDGE, Tenn. -- A two-photon laser technique holds the promise of treating deep-tissue cancers such as early-stage breast cancer, say the scientists who developed the technique. Researchers at Oak Ridge National Laboratory employ a mode-locked Ti:sapphire laser to treat breast cancer cells in in vitro tests.
The main advantage of the technique would be in treating early-onset cancers where surgery is not an option, said Oak Ridge chemist Eric Wachter. Although the researchers are initially studying breast cancer applications, they expect that doctors could use the technique for various types of cancer and other diseases.
The technique uses a near-infrared light source instead of ultraviolet or visible, so less energy is required and physicians can pinpoint cancer cells, reducing the harm done to surrounding tissue.
In a minimally invasive treatment known as photodynamic therapy (PDT), light-activated drugs called photosensitizers and nonthermal, monochromatic light selectively
destroy diseased cells. The photosensitizers are distributed throughout the body and concentrate in diseased tissue. Doctors illuminate the area with light, which activates the agent, killing the tissue and stopping the growth of diseased cells.

Less peripheral damage
Previous PDT regimens have been based on linear, high-energy photochemical methods that do not provide a means for achieving pinpoint activation of the pharmaceutical agent and that may have side effects such as development of secondary skin cancers caused by higher-energy light. These regimens also do not offer the penetration depths reportedly possible using the mode-locked Ti:sapphire laser.
The laser used in the new technique emits in the near infrared at 700 to 1000 nm, making it less likely to induce damaging photochemical processes (i.e., burning of skin and tissue) than treatments that use ultraviolet or visible light. Scientists have shown excitation of cancer cells at depths greater than 8 cm. Wachter hopes that animal trials will begin soon, with dose estimation results expected in 6 to 24 months.

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