Ultraviolet Radiation Therapy Overview

Ultraviolet Radiation Therapy (UVR)

• UVR is electromagnetic radiation between visible light and X-rays.
• Wavelengths range from 400 nm to 100 nm.
• UVR is mostly absorbed within the first 1-2 mm of human skin.
• UVR's physiological effects are usually superficial and non-thermal, mainly chemical.
• Used to treat various skin disorders.
• Divided into three ranges: UVA, UVB, and UVC (germicidal).

The Electromagnetic Spectrum

• Shows the range of wavelengths and frequencies of electromagnetic radiation.
• UV is between visible light and X-rays.
• Wavelengths and examples of their corresponding objects: 3 football fields, 10 feet, 3 meters, 3 centimeters, 1 inch, 30x hydrogen atom diameter.

Classification of UVR

Production of Ultra-Violet Radiations

• Natural source is the sun.
• Artificially produced using mercury vapor lamps.
• Lamps consist of a quartz burner tube, evacuated of air, containing traces of argon gas, and mercury under low pressure for current conduction.
• Electrodes at each end of burner tube.
• Applying current vaporizes mercury, and electron passage establishes UVR arc.

Physiological Effects of UVR

• UVR penetrates skin to a maximum depth of 2 mm.
• Effects include skin erythema (redness).
• Causes tanning, epidermal hyperplasia and vitamin D synthesis.
• These effects are believed to be from chemical excitation and photobiological processes.
• Local effects such as redness and general effects such as vitamin D synthesis.

1- Erythema

• The redness of the skin, and the first observable effect of UVR.
• Energy released if UVR is absorbed causes damage to cells and intracellular structures.
• Extent of damage depends on wavelength and amount of UVR absorbed.
• Damage releases histamine-like substances that cause blood vessel dilation (capillaries).
• Severity directly related to wavelength and intensity of the UVR.
• There are four distinguishable degrees of visible erythema

2- Pigmentation (Tanning)

• Develops within two days of irradiation.
• UVR stimulates melanin (pigment) upward migration from deep epidermis to superficial layers.
• Melanin acts as an umbrella over the cell nucleus, reducing penetration of UVR to deeper tissue layers.
• Tanning is considered a protective response by the body.

3- Growth of Epithelial Cells (Epidermal Hyperplasia)

• Thickening of the skin layer (hyperplasia) starting about 72 hours after UVR exposure.
• Result of repairing process from erythema.
• Proliferation of basal cells to replace damaged/destroyed cells.
• Release of prostaglandin precursors increase DNA synthesis, leading to epidermal hyperplasia.
• Skin thickening is three times greater than before UVR exposure.

4- Desquamation (Peeling)

• Casting off of dead cells from skin surface that are destroyed by UVR.
• Extent of peeling proportional to intensity of erythema.
• Mild erythema may result in fine desquamation after repeated UVR exposure.
• Resistance of skin to future UVR exposure decreases after desquamation.

5- Antibiotic Effect

• Primarily UVB enhances destruction of viruses, bacteria, and microscopic organisms on skin's surface.

B- General Effects of UVR

1- Formation (Production) of Vitamin D

• UVR accelerates vitamin D formation in skin by converting provitamin D in skin like 7-dehydrocholesterol to Vitamin D3.
• Active Vitamin D3 enhances calcium and phosphorous absorption in the intestine.
• Facilitates calcium exchange and bone formation, preventing rickets.

2- The Esophylactic Effect

• Increases body's resistance to infection, especially with general UVR.
• Occurs due to Reticulo-endothelial System stimulation.
• Cells in this system ingest bacteria and produce antibodies.

3- Ageing of the skin (Solar Elastosis)

• Prolonged exposure causes premature aging, due to:
  • Damage to collagen by UVA causing loss of elasticity, wrinkles, and pigmentation.
  • Thinning of epidermis.
  • Loss of epidermal ridges and melanocytes.
  • Dryness due to dysfunction of sebaceous and sweat glands.
  • Wrinkles from the lack of dermal connective tissue.

4- Immune Suppressive Effects

• UVR triggers immunosuppressive effects (both local and systemwide).
• Destroys Langerhans cells, stimulating suppressor T cells that prevent antibody production.
• Prolonged exposure can increase risk of skin cancer due to suppression effect.

5- Effects on Eyes

• Acute exposure to UVC and UVB may lead to:
  • Conjunctivitis (inflammation of inner eyelid membrane).
  • Photokeratitis (inflammation of the cornea, possibly with severe pain).

Therapeutic Uses of UVR

• Acne, Psoriasis, Incipient pressure areas, Wound healing, Eczema.

Acne

• Chronic inflammation of sebaceous glands with duct blockage.
• UVR treatments open pores and follicles, improve skin condition, stimulates healthy epidermis growth, and destroys infection.

Psoriasis

• Inflammatory skin disease with red plaques and silvery scales.
• UVR therapies target to inhibit cell division, decrease DNA synthesis, or alter immune response.

Incipient Pressure Area

• Early stage pressure sores prevented from infection and open wounds by UVR stimulation of epithelial cells and destruction of surface bacteria.

Wound Healing

• UVR, especially UVC, promotes healing of infected and non-infected wounds by increasing epithelial cell production (hyperplasia), increasing blood supply, preventing infection, and destroying infected tissues.

Eczema

• Inflammatory skin response, with itching, redness, and scaling.
• UVR improves condition with erythema and antibiotic effect. Sterilization of skin surface is part of the treatment process.

Photo-chemotherapy

• A treatment strategy for skin disorders using a photosensitizing drug (eg. psoralen) with UVA radiation.
• The drug increases skin sensitivity to UVA.
• Used to treat disorders like psoriasis and eczema

Contraindications

• UVR therapy may be contraindicated in certain conditions like acute eczema, lupus erythematosus, photo-allergy, fever, recent x-ray treatments, pulmonary tuberculosis, tumors, cardiovascular diseases, hyperthyroidism, and present skin redness.