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You are here: Cancer information / Diagnosis and treatment / Photodynamic therapy / Principles

Glossary

Principles

Photodynamic therapy (PDT) is based on the finding that certain chemicals kill cells when exposed to a particular type of light. PDT destroys cancer cells by using laser light in combination with a drug called a photosensitizer, which makes cells sensitive to this light.

 

PDT requires light, a photosensitizer and oxygen. It is usually done in 2 stages:

 

The photosensitizer is given.

  • The photosensitizer is absorbed by all body cells, but stays in cancer cells longer than normal cells.
  • Time is allowed for the drug to concentrate in cancer cells, and be removed from most normal cells, except liver and skin cells.

 

The cells are exposed to a low intensity laser light which activates the photosensitizer.

  • The light causes the photosensitizer to undergo a chemical reaction with oxygen [reactive oxygen species (ROS)].
  • ROS only kills cancer cells in tissue that has been exposed to the light – it doesn't harm most normal cells.
  • The length of time that the light is applied, depends on the size and type of area being treated.

 

Different photosensitizers and sources of light may be used depending on the area being treated. The person being treated will be sensitive to light (photosensitive) for 4 to 6 weeks or longer after the treatment.

References

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