WHAT IS PHOTODYNAMIC THERAPY?
Photodynamic therapy (PDT) is a treatment that uses a drug called a photosensitiser or photosensitising agent, and a particular type of light. When photosensitisers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells.1-3
Each photosensitiser is activated by light of a specific wavelength.3,4 This wavelength determines how far the light can travel into the body.3,5 Doctors therefore use specific photosensitisers and wavelengths of light to treat different areas of the body with PDT.
HOW IS PDT USED TO TREAT CANCER?
In the first step of PDT for cancer treatment, a photosensitising agent is injected into the bloodstream. The agent is absorbed by cells all over the body but stays in cancer cells longer than it does in normal cells. Approximately 24 – 72 hours after injection,1 when most of the agent has left the normal cells but remains in the cancer cells, the tumour is exposed to light. The photosensitiser in the tumour absorbs the light and produces an active form of oxygen that destroys nearby cancer cells.1-3 In addition to directly killing cancer cells, PDT appears to shrink or destroy tumours in two other ways.1-4 The photosensitiser can damage blood vessels in the tumour, thereby preventing the cancer from receiving necessary nutrients. In addition, PDT may activate the immune system to attack the tumour cells.
The light used for PDT can come from a laser or other source of light.2,5 Laser light can be directed through fibre-optic cables (thin fibres that transmit light) to deliver light to areas inside the body.2 For example, a fibre-optic cable can be inserted through an endoscope (a thin, lighted tube used to look at tissues inside the body) into the lungs or oesophagus to treat cancer in these organs. Other light sources include light-emitting diodes (LEDs), which may be used for surface tumours such as skin cancer.5
PDT is usually performed as an outpatient procedure.6 It can be repeated, and may be used with other therapies such as surgery, radiation, or chemotherapy.2
- Dolmans DEJGJ, et al. Photodynamic therapy for cancer. Nat Rev Cancer 2003; 3(5): 380-387.
- Wilson BC. Photodynamic therapy for cancer: Principles. Can J Gastroenterol 2002; 16(6): 393-396.
- Vrouenraets MB, et al. Basic principles, applications in oncology and improved selectivity of photodynamic therapy. Anticancer Res 2003; 23: 505-522.
- Dougherty TJ, et al. Photodynamic therapy. J Natl Cancer Inst 1998; 90(12): 889-905.
- Dickson EFG, et al. New directions in photodynamic therapy. Cell Mol Biol 2003; 48(8): 939-954.
- Capella MAM, Capella LS. A light in multidrug resistance: Photodynamic treatment of multidrug-resistant tumors. J Biomed Sci 2003; 10: 361-366.