What Is Photothermal Therapy?

Photothermal therapy (PTT) is an alternative cancer treatment that uses electromagnetic radiation to kill malignant tumors. There are three kinds of PTT: traditional, plasmonic photothermal therapy (PPTT) and photodynamic therapy. Tradition PTT uses radiation, along with dyes capable of absorbing radiation at the site of the tumor. Plasmonic photothermal therapy relies on infrared or near-infrared light and electron clouds. Photodynamic therapy employs free radicals and radiation with photosensitizers, which are drugs that make the skin more permeable to X-rays.

During photothermal therapy, lasers with wavelengths ranging in length from 650 nm to 980 nm are directed at tumors for several minutes, generally not more than six, obliterating them with localized heat. For all forms of PTT for cancer, there is danger that normal tissue surrounding the tumor may absorb heat from radiation and become damaged. Still, cancer patients are attracted to this photomedicine because it does not require invasive surgery. It is often used to treat breast cancer and prostate cancer.

Certain forms of photothermal therapy have distinct benefits and detriments. One detriment associated with PTT is photobleaching, or a lightening of skin over the area where the tumor is buried, caused by the laser beams used to direct radiation. Two drawbacks are linked PPTT. Plasmonic photothermal therapy cannot penetrate enough to treat deeply buried tumors and it requires the use of photosensitivity drugs that remain inside the body for long periods, causing the skin to be easily burned by light. Photodynamic therapy can reportedly treat deep tumors without bleaching the skin and loading the body with photosensitizers.

Some methods of photothermal therapy use nanotechnology to make the electromagnetic radiation more effective. Nanoshells, minuscule particles with metallic coverings, can intensely absorb radiation. Once inserted into the cancer tumors, nanoshells increase the likelihood that the cells will be ablated by radiation. Some studies suggest phototherapy with nanoshells can be up to 90 percent effective in aiding cancer remission.

To ensure radiation is directed to the right locations and to monitor temperatures of treated body tissues, imaging tools are used to see inside the body during therapy with photomedicine. Such tools include ultrasound, which uses sound waves to create internal pictures. Another tool is photoacoustic imaging, which uses both light waves and sound waves to create an image. The latter can help doctors see how hot cancer tumors and surrounding tissue become during photothermal therapy; this cautionary monitoring can prevent destruction of healthy tissue and verify cancer cells have actually died after being irradiated.