What is Photodynamic Therapy also called PDT ?
What’s the basic idea?
Called PDT (Photodynamic Therapy), PDT is a two-stage therapeutic treatment. First the IV injection of a drug (photosensitizer), followed by a light illumination of the organ to be treated at a wavelength corresponding to the activation wavelength of the injected drug. For example: 630 nm for Photofrin.
How does it work?
The reason of this illumination, at the place of treatment, is to cause a photochemical reaction which will generate the liberation of toxic substances resulting in the cellular death. It is this association of photosensitizer together with monochromatic light, emitted by a laser, which will allow the specific targeting of tumorous cells and their destruction.
What is the light source?
The light source is a diode laser emitting at a specific “monochromatic” wavelength corresponding to the activation wavelength of injected photosensitizer. The wavelength varies from red to near-IR (630 nm to 800 nm) according to type and family of photosensitizer. The effect of treatment and depth of penetration depends of photosensitizer type. Blue light penetration is limited compared to red of near IR-light.
How to bring laser light to treatment site?
In gastroenterology, pulmonology, urology most of PDT treatments are performed by endoscopic solutions. The laser source is coupled to an optical fibre which will be introduced in patient’s body using the biopsy channel of an endoscope to the site to be treated : oesophagus, lungs, biliary tract, prostate, bladder, etc. In dermatology, the light source will be based on panels of LEDs for a direct illumination of skin.
Which tumours can be treated?
PDT has been used for the palliative or curative treatment of numerous types of diseases.