Photo-dynamic Therapy

Photo-dynamic therapy uses light, and has been used to treat other forms of cancer, mainly in the head and neck.

Researchers at University College London are assessing the use of photodynamic therapy for prostate cancer.

Photodynamic therapy uses a drug, based on chlorophyll which is injected into the blood stream and makes the whole body sensitive to light. The drug only works when it is activated by special light from a laser. Thin optical fibres are put into the prostate to deliver the laser light. The activated drug then acts to block blood vessels, and cause death of prostate cells (normal cells and cancer cells).

It is hoped that this treatment could offer less side effects than current treatments such as surgery and radiotherapy. It can be done with a 24 hour hospital visit, and, if proves successful, could be repeated if necessary.

What is photodynamic therapy?

Photodynamic therapy (PDT) can be used as a treatment for many diseases, for example prostate cancer. It uses a drug, called a photosensitiser, which is activated by light, usually from a laser. The activated drug can kill the cells around the light fibre, by producing reactive oxygen species. These are powerful forms of oxygen which can either kill cells directly, or attack the blood vessels which supply the cells.

In photochemical terms, the photosensitiser changes energy levels, moving from ground state, which is at low energy, to singlet state which is higher energy, when it is activated by light from the laser. This singlet state photosensitiser can then either lose energy as light (fluorescence), or as heat, or be converted to an intermediate state known as triplet state. In this form it can then undergo one of two types of reaction with oxygen. This produced the high energy oxygen products which cause the photodynamic therapy effect.

Does photodynamic therapy only kill cancer cells?

Photodynamic therapy, like all of the other treatments for prostate cancer can kill normal cells as well as cancer cells. However, it seems that cancer cells are more sensitive to PDT and normal cells can recover or be repaired much better than cancer cells. It is thought that vascular-targeted photodynamic therapy with Tookad works on the blood vessels supplying cancer cells more effectively than on normal blood vessels. This is one of the aspects of the treatment that is being investigated in current studies.

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