PHOTODYNAMIC THERAPY
Photodynamic therapy (PDT) was introduced into medicine in the 1980s for the treatment of cancer. It involves 3 key components: a photosensitiser, light, and oxygen in the tissues. Photosensitising drugs are trigged by light of a specific wavelength, which causes the formation of an oxygen radical inside the cancer cells that attacks and destroys them from within. PDT has proven to be an alternative treatment for many cancers.
In brain tumours, tumour recurrence occurs within 2 cm of the resection margins. This means that, although increasing the removal of tumoural tissue increases tumour resection and thus the chances of a cure, or at least long-term survival, it also increases markedly the chances of neurological sequelae of Bell’s palsy, loss of the ability to speak, loss of vision…
On the other hand, if a given substance selectively destroys tumour cells while respecting the normal brain tissue, we can increase the destruction of the tumour without increasing the consequences on healthy brain cells. This is the photosensitising drug’s role. It is administered intravenously 4 days before surgery, for 4 days is the time needed for the drug to selectively accumulate in tumour cells. Unfortunately, however, it also accumulates in the skin, and this means that the patient cannot be exposed to sunlight for 15 days, the time needed by the body to remove the remains of the drug.
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During surgery and after completion of surgical resection, a laser light is shone. This causes the destruction of tumour cells in the surgical cavity and at the resection margin within 9mm from the margin, but the laser does not cut or destroy normal brain tissue.
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Photodynamic therapy in the treatment of brain tumors
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HOW IS PHOTODYNAMIC THERAPY CARRIED OUT?
Photodynamic therapy is completed in two stages:
- First, the photosensitising drug is administered by intravenous injection. All the tissues of the body absorb the drug, but it is absorbed by cancer cells in much greater quantities. During the following days the drug is slowly removed from most of the normal cells but remains in cancer cells, as well as in skin cells for about 90 days after injection.
- The second stage occurs 2 days after injection, during surgery, once the resection is finished. The laser light is directed towards tumorous cells in the surgical cavity and resection borders, activating the photosensitising drug inside cancer cells and so causing their death.
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Stages of PDT
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