Photodynamic therapy. Operating principle

Photodynamic therapy (PDT) is a modern method of treating many diseases. PDT systems are actively used in oncology, dermatology, cosmetology, dentistry. At the heart of the treatment principle
there is the effect of monochromatic light with photosensitizers – photosensitive substances that activate their action under the influence of incident light photons. Photosensitizers are preliminarily introduced into the treatment zone (for example, a tumor), after which the radiation exposure occurs according to the protocols laid down in the device (exposure time, power, wavelength, etc.). In this case, the variability of both the treatment method and the location of light-emitting masks or surfaces depending on the treatment zone is possible. Photosensitizers can be administered in a variety of ways – for example, intravenously, orally, and applicationally. Photosensitizer molecules accumulate in the active zone (diseased tissues, cancer cells, etc.) and act as chromophores for light. Depending on the type of sensitizer, a special radiation wavelength of the photodynamic installation is selected, which will be absorbed as much as possible by the active substance. The main mechanism of action of molecules of the active substance on tissue is the reactions that occur after the absorption of light particles. As a rule, irradiated particles react actively with oxygen molecules, converting their state from triplet to singlet and, thus, contributing to the formation of a large number of radicals. The formed radicals and singlet oxygen actively act and destroy damaged cells.

Scope of PDT

Photodynamic therapy can be effectively used in the treatment of the following diseases:

1. Various oncological diseases.
2. Dermatitis, psoriasis, acne and other skin diseases.
3. Allergy.
4. Viral diseases (such as herpes, hepatitis B and C).
5. Bronchial asthma, etc.

Contraindications

There are few contraindications to PDT. Therapy is not recommended in the following cases:

1. Mental disorders.
2. Blood diseases.
3. Hypotension.
4. Pathology of the kidneys and liver.
5. Hypersensitivity to the drug or its components.

Benefits of PDT

Photodynamic therapy is a fairly popular procedure and is actively gaining even more popularity due to the following advantages:

1. The lack of direct surgical intervention, which allows this procedure to be performed by the elderly.
2. The absence of systemic complications after the procedure.
3. The possibility of use as part of complex therapy or as an independent method of treatment.
4. Lack of pain.
5. Quick recovery after the procedure.

The disadvantages of PDT

Despite the large list of advantages, photodynamic therapy has several disadvantages:

1. PDT is limited to the area of light penetration, which limits its use.
2. The following side effects are possible – increased sensitivity to light, cough, difficulty swallowing. These side effects pass quickly enough. But for a while it is worth avoiding the appearance of the sun.

PDT stages

Photodynamic therapy includes the following stages:

1. The introduction of photosensitizers into the blood or onto the skin (depending on the location of the tumor or damaged area).
2. Activation of photosensitizers using low-intensity laser radiation (a power level of 1 – 2 W is sufficient). Low radiation intensity suggests the optional use of painkillers.
3. When irradiated, the photosensitizer molecules absorb the laser radiation and start the photochemical process, during which atomic oxygen and high activity radicals are released. Cells in the inflamed area break up into separate fragments and are destroyed. In the same way, blood vessels that deliver blood to the tumor are eliminated.

To achieve a positive effect, usually 1 procedure is enough. Within 1 – 1.5 months, the tumor disintegrates and is replaced by a new connective tissue.

Drugs used in PDT

The PDT photosensitizers that are currently in use have rather stringent requirements:

1. Lack of toxicity.
2. High absorption in certain parts of the spectrum.
3. Ensuring the release of atomic oxygen.

Therefore, photosensitizers are often used, for example, derivatives of chlorin (maximum absorption at a wavelength of 660 nm), phthalocyanine (675 – 698 nm), hematoporphyrin (630 nm).

PDT devices

Due to the significantly increased interest in photodynamic therapy units from both medical institutions and aesthetic clinics, a large number of different PDT devices appear on the market. The main characteristics that you should pay attention to when choosing an apparatus are radiation power, the ability to select different wavelengths (for treating various diseases), exposure time and other software settings in combination with treatment protocols.

According to the type of emitting heads, LED and laser installations are distinguished. Laser medical devices include sets of laser diodes that generate more monochromatic radiation than LEDs with a certain wavelength, therefore their efficiency is higher and less power is required than when using LED masks.