What Is the Photodynamic Therapy(PDT)?

 

Photodynamic therapy (PDT), also known as photosensitivity or photochemistry therapy, its principle is to selectively accumulate the photosensitizer in the target tissue, and then to stimulate the photosensitizer with a specific wavelength of light to produce a photochemical reaction to treat the disease.

In virtue of its many advantages, especially in terms of tumor treatment, it is called the fourth therapy after radiotherapy, chemotherapy and surgical treatment. Mature PDT has achieved great success in the United States, Japan, the United Kingdom, France, Germany, Canada and other countries, and has been widely used in various fields such as postoperative analgesia, vasculology, gynecology, dermatology and many other clinical practices.

Photosensitive therapy must have three conditions: light source, photosensitizer, and target tissue. Common light sources include visible light, ultraviolet light, and lasers. Photosensitizers are substances that can absorb light at a certain wavelength and can be activated by it. Common photosensitizers include coal tar, flavor coumarin, 8-methoxy psoralen, Yelin, photosensitive drugs, and phthalocyanine compounds. Target tissues include the skin, blood, bone marrow, tumors, and other tissues.

The specific operation examples are as follows:

1.Treatment of psoriasis and vitiligo:

First, 20-30mg of 8-methoxy psoralen (8-MOP) was taken orally, and systemic UV irradiation was administered 2h later. In the treatment of localized psoriasis and vitiligo, 0.15%~0.5% of the 8-MOP tincture was applied to the affected skin, and long-wave UV irradiation was performed after 40min. The alternate day was radiated once and 20-30 times was a course.

2.Treatment of PDT for malignant tumors:

①　Do an allergy test on the patient's forearm before giving hemelin medication, if the result is negative, the drug was administered 2.5-5mg/kg as prescribed, and the drug was dissolved in 250ml of normal saline and injected i. v.

②　Generally, laser irradiation was started 48–72h after drug injection, and the light source can be irradiated locally with a high-power 630nm red light laser for 20-30min.

③　Direct irradiation of the body surface locally to treat the body surface malignancy，or use of endoscopy, optical fiber for body cavity irradiation to treat the oral cavity, esophagus, stomach, bladder and other body cavity tumors.

④　Generally, after 24h of treatment, the tumor becomes black and necrotic, forming a black scab after 1 week, and falling off after 2-3 weeks.

⑤　Treatment is performed 1-2 times, and reirradiation should be conducted after one week interval.