What is targeted phototherapy?
Phototherapy consists of the delivery of light or ultraviolet radiation to treat various skin disorders. This field has seen several major advances over the years, the most recent being targeted phototherapy.
Targeted phototherapy, also called concentrated phototherapy, focused phototherapy and microphototherapy, involves delivery of ultraviolet radiation directly focused on, or targeted at, the skin lesion through special delivery mechanisms.
The term 'targeted phototherapy' includes laser and nonlaser technologies.
Advantages of targeted phototherapy over conventional phototherapy
Several advantages have been claimed for targeted phototherapy.
- Exposure of involved areas only and sparing of uninvolved areas, thus minimizing acute side effects such as erythema (sunburn) and long-term risk of skin cancer in unaffected skin.
- Quick delivery of high-doses of energy and short treatment sessions.
- Less frequent and numerous visits to clinic, reducing patient inconvenience.
- Allows treatment of difficult areas such as scalp, nose, genitals, oral mucosa and ears.
- Targeted phototherapy machines occupy less space. Large office space is required to house the bulky machines used in conventional phototherapy.
- Easy administration for children. Children are intimidated by large machines used in conventional phototherapy.
Disadvantages of targeted phototherapy
- Targeted phototherapy units can be more expensive than conventional phototherapy units.
- Targeted phototherapy is not recommended if lesions occur over more than 10% of the body area.
- They are not adequate to treat extensive areas of skin in view of the cost of treatment and time involved in treatment.
Indications for targeted phototherapy
Examples of skin conditions that may be treated by targeted phototherapy include:
- scalp psoriasis
- seborrhoeic dermatitis
- cutaneous T-cell Lymphoma (mycosis fungoides)
- atopic dermatitis
- pityriasis lichenoides
- urticaria pigmentosa
- hand dermatitis
Mechanism of action
Most targeted phototherapy devices (laser or nonlaser type) emit radiation in the UVB range, with peak emission in the narrowband wavelength (around 308-311 nm), while some non-laser machines emit UVA radiation also.
The following mechanisms have been proposed to explain UV's efficacy in the treatment of skin diseases:
- Apoptosis of pathogenically relevant cells including T-cell apoptosis in the treatment of psoriasis, mycosis fungoides and atopic dermatitis, and mast-cell apoptosis in pruritic skin disorders.
- Stimulation of melanocyte-stimulating hormone, increased melanocyte proliferation, and melanogenesis as in vitiligo.
- Decreased release of histamine from both basophils and mast cells in histaminic disorders such as urticaria pigmentosa.
- UVB radiation has several other effects on skin, such as alteration in cytokine production, and local immunosuppression which helps in skin disease treatment.
Devices for targeted phototherapy
Targeted phototherapy depends on devices that can emit non-ionising radiation that can penetrate the affected area of skin. This can be achieved using different laser and non-laser sources.
Excimer lasers operate in the ultraviolet range. Examples include the 193-nm argon-fluoride; 248-nm krypton-fluoride; 351-nm xenon-fluoride; and of particular interest to dermatology, the 308-nm xenon-chloride laser. These lasers utilize a mixture of a noble gas and a halogen as a lasing material.
FDA-approved excimer laser machines have been introduced by companies such as Photomedex (XTRAC®; USA) and Alcon (Wave Light®; USA).
These machines have several disadvantages such as high cost, huge weight and bulk, and difficulties in maintenance. They are available at only at a few specialist centres in the US.
Monochromatic excimer therapy
Sources of monochromatic excimer non-laser targeted phototherapy include Excilite® (DEKA, Florence Italy; 304nm), Pxlite (308nm) and Exciplex (Excimer Therapies; 308 nm). These machines are less bulky, cheaper, and have a comparatively larger treatment surface in contrast to excimer laser.
Non-laser targeted phototherapy
Advances in technology have now permitted targeted delivery of conventional sources of broadband or narrowband UV radiation.
Most of these machines use a conventional high-pressure burner emitting UV light. Fibre-optic cable systems deliver energy directly to the lesion.
An added advantage of some of these machines over the excimer systems is that both UVA (330-380 nm) and UVB (narrowband; 290-330nm) spectra are available.
These machines have multiple delivery programs and automatic calibration for quick delivery of predetermined dosages, so that treatment time is short.
They are considerably smaller in size than the laser machines, with less maintenance problems, and are also cheaper.
Several machines have been marketed in recent years outside USA including Dualight® (Theralight Inc USA; emits both UVA radiation in the range 330-380 nm and UVB in the range 290-330 nm) and Bioskin® (narrowband UVB 280-300nm, available only in Italy). Other targeted phototherapy units available in USA and marketed by Daavlin (Ohio, USA) include Levia® and Lumera®.
Safety of targeted phototherapy
Ultraviolet radiation exposure leads to skin ageing and skin cancer. The risks are lower when limited skin is exposed to it, as is the case with targeted phototherapy.
- UVB may cause acute phototoxicity (like sunburn), with redness and blistering, beginning in the first 4–6 hours after exposure and peaking at 12–24 hours.
- Male genitalia should be shielded during every treatment session as they are particularly sensitive to the development of skin cancers.
Contraindications for targeted phototherapy
Absolute contraindications to any form of phototherapy include:
- Xeroderma pigmentosum
- Systemic lupus erythematosus
- Basal cell naevus / Gorlin syndrome
- Photosensitivity disorders
- History of malignant melanoma
Relative contraindications to phototherapy include:
- Young age
- Risk factors for melanoma, e.g. many moles
- History of nonmelanoma skin cancer
- Photosensitizing medications
- Significant past UV exposure (sun damage)
- History of arsenic exposure, ionizing radiation, cyclosporine, or other immune suppressing medications