Definition and Overview

Photodynamic therapy (PDT) is both a cosmetic procedure and non-invasive surgical treatment for a variety of conditions including certain types of cancer, such as esophageal cancer, non-small-cell lung cancer, and pre-skin cancer lesion. It involves two components: a drug generally called photosensitizing agent and a light.

Also referred to as blue light or photochemotherapy, photodynamic therapy uses various kinds of light such as laser, blue light, and LED to activate the components of the drugs to destroy damaged tissues and abnormal cells.

Compared to other forms of skin and cancer treatments, PDT is much cheaper and safer. In fact, unlike radiotherapy, it can be applied to the same site multiple times without putting the patient at risk. Although there are side effects like sensitivity to light and burning sensation, these typically subside within a few days after the treatment.

PDT is an outpatient procedure and patients are allowed to go back to normal activities following the treatment so long as they avoid direct sun exposure for about a week.

Nevertheless, the therapy has also its own limitations. Although the wavelength of light can greatly vary, it cannot reach the deeper layers of the skin and tissues. Hence, the therapy may not work on cancers that have already penetrated the skin's deepest layers. Further, PDT treatments are localized; hence they are not effective on cancer that has already metastasized (has spread to other organs).

As to the drugs used, so far, there are three that have been approved by the Food and Drug Administration (FDA). These are porfimer sodium, ALA (aminolevulinic acid), and methyl ester. Porfimer sodium is the one recommended for the treatment of cancer that affects the internal organs and it is typically delivered through the veins while the other two are applied to the skin. ALA, meanwhile, works with blue light while methyl ester is activated by red light.

Photodynamic therapy is performed by trained dermatologists, oncologists, and technicians.

Who should undergo and expected results

The FDA has approved the use of PDT for the treatment of esophageal cancer and non-small-cell lung cancer. However, patients who have fistula or enlarged veins do not qualify for this treatment. Clinical trials on PDT are now working on using the technology to treat liver, stomach, cervical, and prostate cancer. By then, the light should be able to travel much deeper.

It is also popularly used in treating actinic keratosis (AK). It is a pre-skin cancer lesion characterized by scaly or crusty overgrowths on the face, scalp, back of the hands, and lips. It is caused by regular, prolonged exposure to the sun, resulting in severe sun damage. Meanwhile, dermatology clinics are utilizing PDT for treating moderate to severe cases of acne as it is proven to be highly effective in minimizing large pores, non-pitted scars due to acne, and early skin damage due to sun exposure.

The treatment is not recommended for people who have porphyria (a hereditary blood disorder caused by porphyrin buildup) and systemic lupus erythematosus (SLE).

The outcomes of the therapy will differ depending on the condition being treated, the type of drug and light used, and the body's overall response to the treatment. Some people may experience dramatic improvement following only one session while others will not find PDT helpful at all. Usually, it takes at least 4 weeks before the expected results are seen.

Those who have compromised immune system such as patients with HIV or AIDS need to work closely with their doctor before undergoing PDT.

How the procedure works

As there are several drugs and light therapies, there are also a couple of methods used when performing photodynamic therapy. If the problem is within or near the skin surface, the agent is usually delivered topically. Otherwise, it will be introduced into the body using an IV, which is usually the case when it is for a cancer treatment. The agent will find its way into the body's cells. While the normal cells will get rid of them, the agent moves closer to the cancer cells. This process may take some time and usually, light is delivered to the cancerous organ after three days following the administration of the drug.

PDT for skin is easy since lesions are often seen. For cancer, the light is normally delivered through a fiber optic cable or an endoscope, a flexible tube that can go all the way to the organ. Since the light works only on cells with the agent, only cancer cells should be destroyed.

If PDT has to be applied to the skin, the skin should first be cleansed and degreased before the drug is applied to the target area and the light administered.

In PDT, only local anesthesia is needed.

Possible risks and complications

Most patients develop sensitivity to light (photosensitivity), as well as burning or tingling sensation, especially on the skin. However, these should diminish over time. Scarring and swelling of nearby tissues may also be observed.

References:

  • Cancer Research UK
  • MacMillan Cancer Support
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