Synonyms in a broader sense
Definition – What is photodynamic therapy?
Photodynamic therapy is a procedure that is intended to have a healing or soothing effect on skin tumors and vascularization and consists of light irradiation in combination with chemicals.
The method of photodynamic therapy
The idea behind photodynamic therapy is to damage and destroy degenerated cells by light irradiation. In this process, the patient is injected with a photosensitizing substance (photosensitizer), which is distributed throughout the body and accumulates mainly on the affected tumor or skin cells. If it is a skin tumor that is to be treated, the sensitizing substance can also be applied to the skin.
The accumulating and sensitizing substance acts as a target marker, which is then illuminated by light of different wavelengths (photodynamic therapy). The light also reaches surrounding tissue, but a reaction only takes place in the previously accumulated area. When the light rays meet the photosensitizer, so-called oxygen radicals are formed as a chemical reaction. These radicals damage the diseased tissue and the diseased cells die (photodynamic therapy).
Application areas of photodynamic therapy
Originally, photodynamic therapy was tested and applied in the treatment of skin tumors. The main reason for this was that the light emitted had only a low penetration depth, so that the skin surface and the tumors present there could be reached with complete certainty. In addition to various forms of cancer, the so-called actinic keratoses, warts and basaliomas, Bowen`s Disease, spinaliomas, skin T-cell lymphomas, Kaposi sarcomas, keratoacanthomas, psoriasis vulgaris, human papilloma virus, molluscum contagiosum and acne can be treated with photodynamic therapy.
In dermatology, the sensitizing dye is usually not injected but applied to the skin. MAOP (Methyl 5-Amino 4 Oxopentanoate) is used as a cream. Due to its molecular structure, the substance accumulates particularly in pre-damaged tissue.
The exposure time is 3 hours. Afterwards the corresponding area is irradiated with a red light. A so-called cold red light with a wavelength of 630 nm is used (photodynamic therapy).
When the light radiation hits the tissue, oxygen radicals are produced, which are released into the correspondingly illuminated tissue. Complex biochemical processes finally cause the affected cells to perish. The very specific irradiation spares the surrounding healthy tissue and usually does not cause scarring.
If it is not clear at the beginning of a treatment whether photodynamic treatment can help, a sample biopsy is first taken and examined. The actual photodynamic treatment then starts one week later. At the first session a period of 3-5 hours must be planned.
The photosensitizing cream is applied to the affected area in a thickness of about 0.5 to 1 mm and then sealed with aluminum foil. The procedure can be performed on an outpatient basis and patients can often leave the doctor’s office during this time. One hour before the radiation begins, the patient must take painkillers.
Shortly before the irradiation, a local anaesthetic pain gel is applied to inhibit the acute pain. Afterwards the irradiation begins with cold red light. After the treatment, the irradiated area is coated with anti-inflammatory and cooling creams.
The application should also be done 3-4 times a day in the following days. Cooling bandages can also help to alleviate the locally triggered inflammatory reactions. Photodynamic therapy is also used in the field of anti-aging.
Here, old cells and cells that have been pre-damaged, e.g. by long exposure to sunlight, are to be killed by the radiation. The irradiation time is about 30 minutes. Here, too, the irradiation should be repeated with a 10-day interval (photodynamic therapy).
Another field of application is ophthalmology. At the so-called age-related macular degeneration an attempt of therapy with the photodynamic therapy can also be made. This is a relatively new treatment method of the so-called choroidal neovascularization, a pathological formation of new blood vessels which often results in a macular degeneration.The dye verteprofin is allowed to enter the patient’s vein for 10 minutes.
During this time, the dye accumulates in the vascular endothelia of the diseased choroidal vessels and sensitizes them to light. After enrichment, the cells are sclerosed over a period of 82 seconds with a red non-thermal laser light. Since the dye also enriches other areas, i.e. the surrounding area, the treatment must be carried out in the dark.
During the time after the treatment (photodynamic therapy) there is still dye in the tissue of the eye and the surrounding skin. For this reason the patient must strictly protect himself from light even after the treatment, wear special sunglasses with long sleeves and should not leave the house. This rest period is recommended for about 48 hours.
Ophthalmologic examinations should not take place during this time either. Actinic keratosis usually refers to superficial preliminary stages of skin cancer. These are malignant (malignant) altered cells that can develop into skin cancer within a short time.
Photodynamic therapy can target these cells and thus prevent the development of real skin cancer. Photodynamic therapy is particularly well suited for large-area extensions of actinic keratosis. Since photodynamic therapy only reaches the superficial cell layers, skin cancer that has already established itself in deep skin layers can no longer be prevented with photodynamic therapy.
- How can actinic keratosis be recognized?
- Actinic keratosis – what is the best therapy?
Photodynamic therapy is not only suitable for skin cancer precursors; in recent years, an expanded treatment spectrum has emerged. In the meantime, various forms of basal cell carcinoma (white skin cancer) can also be treated. However, the photodynamic therapy does not reach the deep skin layers, so the treatment is only profitable in the case of a superficial basal cell carcinoma.
For additional information on this topic, our main article is suitable: Basalioma – Information about white skin cancerTo treat macular degeneration in ophthalmology a 2-3 times repetition of the irradiation (photodynamic therapy) has to be planned. In the dermatology two irradiations are carried out at first. Between them there should be 7-10 days.
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