How Is PhotoDynamic Therapy Performed

Photodynamic Therapy (PDT) also known as photoradiation therapy isused to treat numerous skin conditions, most commonly actinic keratoses and superficial nonmelanoma skin cancers. This involves exposure to a photosensitizer followed by light activation and resultant cell death through the formation of singlet oxygen and other free radicals.

Photodynamic therapy has been reported in the early 1900’s and its used by dermatologist to treat actinic keratoses and superficial nonmelanoma skin cancer. Most recently it has also been reported to be effective in the treatment of acne vulgaris, sebaceous hyperplasia, localized scleroderma and many other infections like psoriasis, HPV,  molluscum contagiosum.

How Is PhotoDynamic therapy Performed ?

Patient undergoing PDT is first exposed to a photosensitizers. Photosensitizing agent may be either systemic ( porphimer sodium like photofirn) or topical (5-aminolevulinic acid- ALA). Typically 20%,  ALA solution ( with 40% ethanol) is applied to the area to be treated and left for several hours (14-16 hrs). But new study suggest that shorter incubation time (15-60 minutes) does not decrease the effectiveness of treatment but may help minimize side effects and increase treatment convenience.

After an appropriate incubation time, the patient is exposed to a light source. Many different light source have been used,  such as incoherent sources ( slide projectors, halogen lamps, xenos lamps and fluorescent lamps ), blue light (405 to 420 nm), red light (635 nm), pulse dye lasers (585 nm) and intense pulsed light sources (500-1200 nm). Depth of penetration is propotional to the wavelength of the light source. So, longer wavelength may be more effective in treatment of thicker skin lesion, whereas shorter wavelength may be used for superficial skin lesion.

Recommended times of exposure and light dosing vary considerably, depending on the disease and the light source used. Photodynamic Therapy may be repeated at various interval if needed.

You may have Stinging, burning, itching and localized erythema and edema at the treatment site . Pain and hyperpigmentation of the treated site are less common but can occur especially if treating for acne. Treated lesion often exhibit scaling and crusting followed by healing in 2-6 weeks. Severe reaction such as blistering and ulceration are rare and may signify overexposure to light or increase sensitivity to light.