What is photodynamic therapy?
Photodynamic therapy exploits photochemical processes to treat certain diseases. Namely, the chemical reactions triggered by light create substances that are toxic to certain types of cells and help destroy abnormal tissue.
For photodynamic therapy, a so-called photosensitizer is applied to the area to be treated or injected into the tissue and irradiated with light of a specific wavelength. The photosensitizer is a chemical agent that is stimulated by the irradiation to form cell-toxic substances. This reaction is dependent on oxygen, which is already naturally present in the tissue.
Cell damage (by photodynamic therapy is divided into primary cytotoxicity, which mainly damages cells, and secondary cytotoxicity, which affects blood vessels. Since the photosensitizer is predominantly enriched in the diseased tissue, healthy tissue can be largely spared during this therapy.
When does one perform photodynamic therapy?
Photodynamic therapy plays a central role in the treatment of dermatological diseases.
- skin cancer (basal cell carcinoma, squamous cell carcinoma, actinic keratoses, Bowen’s disease, Kaposi’s sarcoma, mycosis fungoides) and metastases of the skin
- Acne (Acne vulgaris)
- Warts (verrucae) caused by human papilloma viruses
Another area is palliative cancer medicine (palliative oncology), where the disease can no longer be cured, but can be alleviated. The effectiveness of photodynamic therapy is limited by the shallow penetration depth of the light. It is used for these types of cancer:
- Bladder cancer
- Early carcinomas of the lung and esophagus
- Bile duct carcinoma
- Breast carcinoma
- Brain tumors
Photodynamic therapy is also becoming established in ophthalmology, for example in “age-related macular degeneration”.
What do you do during a photodynamic therapy?
Before the actual therapy, your doctor will ask about your health history and rule out contraindications such as allergies to the photosensitizer or pregnancy.
Now a photosensitizer, usually in the form of a cream, is applied to the area to be treated (topical application) and should be left on for at least three hours. For this purpose, 5-aminolevulinic acid has become established, which is metabolized to protoporphyrin, especially by tumor cells. If a photosensitizer is to act throughout the body (systemically) and be administered via the blood vessels, the administration of porphyrins and their derivatives is preferred.
For the photosensitizer to be activated, it must be irradiated with the aid of a laser. Only the absorption of light of the correct wavelength leads to the activation of the substance in question. This is also referred to as a higher-energy state, through which the substance is able to transfer energy to oxygen that is already present in the tissue.
This is converted into a more energetic form (singlet oxygen), which can now damage cells and their components through its chemical reactivity, which is why the term oxygen radical is also used.
The primary cell damage (cytotoxicity) takes place at the components and the membrane of the cells. Secondary cytotoxicity, through effects on the blood vessels, leads to an undersupply and finally to the death of the diseased or degenerated cells.
The actual photodynamic therapy lasts only 10 to 30 minutes and is usually repeated at intervals of one week. To ensure that you do not feel any pain during the treatment and afterwards, you will be given either painkilling medication or pain-relieving gels or creams.
What are the risks of photodynamic therapy?
Side effects cannot be ruled out with photodynamic therapy, but they rarely occur:
- Pain during irradiation
- @ Reddening of the skin (erythema)
- Pustules
- superficial skin lesions (erosions)
- dark discolorations (hyperpigmentation) of the skin
- allergies to the photosensitizer
- crust formation due to the rejection of destroyed cell layers
- scarring
- on the eye: deterioration of visual acuity up to blindness
What do I have to pay attention to after a photodynamic therapy?
Since photosensitizers cause high sensitivity to light, you must protect yourself from sunlight as well as other strong light sources and especially laser light for at least one month after treatment.
Your doctor will tell you how long you should stay out of the sun and what creams and soaps you should use to care for the treated areas. If photodynamic therapy was used for the treatment of macular degeneration, it is recommended to wear sunglasses for some time.
