9.3.4 Basics of ultraviolet radiation therapy and lasers

• Ultraviolet (UV) radiation therapy: phototherapy
• Photochemotherapy (PUVA)
• Photodynamic therapy: photoradiation therapy
• Extracorporeal photopheresis
• Laser (light amplification by stimulated emission of radiation)

The following physical radiation methods should be reserved for medical specialists routinely dealing with the diseases described below.

UV radiation therapy (phototherapy) consists in the use of UVB/A light in the treatment of skin diseases.

Photochemotherapy consists in the use of UVA light and oral or topical photosensitizer of the psoralen type.

Photodynamic therapy consists in a photochemical reaction, which requires the presence of a photosensitizing molecule, photoactivating wavelengths of light and tissue oxygen.

Extracorporeal photopheresis consists of extracorporeal exposure of patient’s blood immune cells, psoralens and UVA.

Laser therapy consists in the emission of coherent radiations using unique light sources rooted in the process of stimulated emission. Different laser types with different wave lengths emissions.

Radiofrequency consists in an oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range 20 kHz-300 GHz.

Soft and hard X-rays are X-rays with high photon energies (above 5-10 keV, below 0.2-0.1 nm wavelength) defines hard X-rays and while those with lower energy and longer wavelength, soft X-rays. Hard X-rays are widely used to image the inside of objects for their penetrating ability in medical radiography. Soft x-ray irradiation is usually used to treat skin-related diseases (including non-melanoma skin cancer and cutaneous lymphomas).

UVB phototherapy (broadband: 290-320 nm; narrowband: 311-313 nm; excimer laser: 308 nm) refers to the use of artificial UVB radiation without the addition of exogenous photosensitizers. The radiation is absorbed by endogenous chromophors and the subsequent photochemical reactions cause a variety of biologic effects, ultimately leading to the therapeutic effects. The most important chromophore for UVB is DNA photoproducts, in particular pyrimidine dimers. UVB exposure reduces DNA synthesis and induces the expression of the tumor suppressor gene p53, with a subsequent cell cycle arrest or apoptosis of keratinocytes if the damage is too severe to be repaired. In addition, UV radiation exerts immunomodulatory activities.

UVA phototherapy (320-400 nm) is subdivided in UVA1 (340-400 nm) and UVA2 (320-340 nm). UVA2 is similar to UVB in the ability to cause erythema as well as immunomodulation and photocarcinogenesis. UVA1 radiation, because of the longer wavelength, penetrates more deeply into the skin layers, and consequently not only the epidermis, but also dermis and blood vessels.

Photochemotherapy with psoralens (PUVA) combines the use of psoralens (P) and long-wave radiation (UVA). Psoralens can be administered orally or topically in solutions, creams or baths, with subsequent UVA exposure. This combination results in a therapeutic phototoxic and immunomodulating effect.

Extracorporeal photochemotherapy (photopheresis) consists in the induction of an immune response against malignant cells (for example, circulating cutaneous T-cell lymphoma cells), downregulation of Graft vs Host reaction on host immune cells and solid organ transplantation reactions. This acts throughout the induction of the generation of antigen-specific regulatory T-cells.

Photodynamic therapy is a photochemical reaction throughout the use of a photosensitizing molecule, which may be administered systemically as intact macrocycles or topically as pro-photosensitizers, which are metabolized to photoactive molecules (protoporphyrin).

Lasers therapy can be delivered in continuous and pulsed waves. The specificity of each laser is characterized by a destruction of specific target structured of the skin, with limited damage of surrounding tissues, via utilization of a wavelength of light preferentially absorbed by the target.

Non-ablative radiofrequency is a procedure commonly used in skin aging for the treatment of skin laxity and wrinkles from an increase in tissue temperature. The main physiological effect is to induce thermal damage to thus stimulate neocollagenesis in deep layers of the skin and subcutaneous tissues.

Soft and hard X-rays: hard X-rays are widely used to image the inside of objects for their penetrating ability in medical radiography. Soft x-ray irradiation is usually used to treat skin-related diseases (including non-melanoma skin cancer and cutaneous lymphomas).

nbUVB: psoriasis, mycosis fungoides, vitiligo, atopic dermatitis, graft-versus-host-disease (GVHD), pityriasis lichenoides, lymphomatoid papulosis, seborrheic dermatitis.

UVA1: localized scleroderma, chronic sclerodermoid GVHD, urticaria pigmentosa, cutaneous T-cell lymphoma (CTCL).

PUVA: psoriasis, mycosis fungoides, atopic dermatitis, lichen planus, GVHD, miscellaneous dermatoses.

Photopheresis: Sezary syndrome, erythrodermic CTCL, acute and chronic GVHD after allogeneic stem cell transplantation.

Photodynamic therapy: neoplasias, such as actinic keratosis, actinic cheilitis, in situ and invasive squamous cell carcinoma, basal cell carcinoma, mycosis fungoides, Paget’s disease, port-wine stains; acne, porokeratosis, leishmanias, photodamage.

Laser therapy: Vascular lesions:  pulsed eye, variable-pulsed potassium titanyl phosphate (Nd:YAG), long-pulsed alexandrite, long-pulsed diode, long-pulsed Nd:YAG, intense pulsed light; endovascular application throughout diode laser, Nd:YAG, radiofrequency energy source. Pigmented lesions and tattoo removal: Q-switched lasers such as Q-switched Nd:YAG, frequency-doubled, Q-switched ruby, Q-switched alexandrite, Q-switched Nd:YAG; long-pulsed lasers and intense pulsed light such as long-pulsed ruby, diode, Nd:YAG, intense pulsed light source. Laser hair removal with long-pulsed lasers such as ruby, alexandrite, Nd:YAG (moderate efficacy) and diode (high efficacy); with intense pulsed light source (low efficacy). Laser skin resurfacing superficial (non-ablative): vascular lasers such as pulse dye and pulsed potassium-titanyl-phosphate laser; mid dermis with infrared lasers or intense pulsed light; deep dermis (ablative lasers): carbon dioxide lasers (pulsed and scanned-continuous wave) and erbium:YAG laser.

UV light: depending on UVB range, erythema peak with 313nm. Acute: itchy or painful erythema, burns with blistering, increased recurrence of herpes simplex viral infections.

UVA and UVB can induce persisting cell mutations, skin cancer risk. Chronic: xerosis, photoaging, carcinomas (basal-cell carcinoma).

PUVA therapy: long term risk of skin cancer, PUVA freckles, gastrointestinal intolerability for psoralens. Photodynamic therapy and Laser therapy may be painful depending on area and dosing.