Learning Objectives
- What is Non-Ionising Radiation
- Sources of non-laser optical equipment in healthcare (phototherapy and dosimetry)
- The body that advises on Non-Ionising Radiation (NIR) protection
- The hazards of NIR
- UK Regulations
- Examples of Exposure Calculation
NIR is radiation that does not produce ionisation. In healthcare the term is largely used to indicate both electromagnetic radiation and ultrasound (mechanical energy). Usually the wavelengths are greater than 100nm.
Electromagnetic radiation is made by quanta, i.e. photons. Each photon carries a finite energy (E) dependent upon the frequency (v) of the EM wave.
where λ is 100 nm, h = 6.626x10-34 Js (Planck’s constant), C = 3x108 ms-1 (speed of light)
The minimum energy required for ionisation is about 12 eV. Photons need v < 100nm to have such energy.
There are two types of NIR, laser and non-laser radiation:
This is broad band optical radiation, produced by spontaneous incoherent emissions of excited materials (i.e. Gas, Semiconductors junctions).
Phototherapy units exploit UV light (mostly fluorescent tubes) to treat skin diseases such as psoriasis. They work by interacting with the immune system and mechanisms of skin regeneration.
Different wavelengths have different penetrations in the skin and are more suitable for different diseases. The cabins are the most common Phototherapy units, or there are treatment beds for longer treatments. Hand and Foot units are used for partial disease or to top up radiation. The hands and feet are often used to exposure to NIR (from the sun) so need a higher dosage. There is also a comb unit if a disease is present on the scalp of a patient’s head.
Examination lights use both UV and visible lights. They can use a variety of light sources: UV compact fluorescent tubes, halogen and LED lights. The region of emission will depend on the specific source used.
Therapeutic sources that exploit the specific interaction of blue light with either the body or the materials (dentistry). They can used fluorescent, halogen or LED sources.
Other typical non-laser sources include Infra-red used in Gate analysis
Ultraviolet (UV) light is used to treat skin diseases. There are different spectra available. A dermatology consultant will recommend the use of one of them after assessing the patient. The starting treatment dose is chosen on the basis of the patient’s skin type or a test dose or (better) both. Phosphor coating on materials can be selected to obtain different spectral outputs.
Typical phototherapy lamps emit the following spectra:
The longer the wavelength of UV light the further it penetrates into the skin
The light dose for patients exposed to a UV phototherapy source (D), is estimated in terms of radiant energy received for unitary surface and measured in Jm-2 (or often in practice as mJcm-2). The dose (D) can be calculated by the knowledge of a source irradiance (E) and patient exposure time (T).
$ D = ET $
D (Jm-2), E (Wm-2), T (s)
This is a non-profit independent body that disseminates information and advice on potential on potential health risk linked to non ionising radiation (NIR). It has a main commission of 14 scientific experts with 4 standing committees (7 members):
Heff = 30 Jm-2 in 8hr (eye, skin)
HUVA = 104 Jm-2 in 8hr (eye - lens)
(ICNIRP - 2010)
Optical radiation can undergo transmission, reflection, refraction, diffraction, adsorption, scattering. UV photons above the ionisation energy can disrupt atoms and molecules. UV photons below the ionisation energy are strongly absorbed in producing electron transitions.
Exposure to UV can affect either the skin or the eyes. UV radiation produces photochemical damages. The photons absorbed have enough energy to induce modifications into the molecules.
Exposure to intense visible light can cause retinal damage. The hazard is highest at those wavelengths the photoreceptors of the retina are most sensitive to 450-550 nm.
| Wavelength nm | Part of the body | Hazard |
|---|---|---|
| 180 - 400 (UVC, UVB, UVA) | Eye (cornea, conjunctiva, lens), Skin | Photokeratitis, Conjunctivitis, Cataractogenesis, Elastosis, Skin Cancer |
| 315 - 400 (UVA) | Eye (lens) | Caractarctogenesis |
| 300 - 700 (Blue light) | Eye (retina) | Photoretinitis, Retinal burn |
| 780 - 1400 (IRA) | Eye (cornea, lens) | Retinal burn |
| 780 - 3000 (IRB) | Eye (cornea, lens) | Corneal burn, Cataractogenesis |
It shall be the duty of every employee while at work to take responsible care for the health and safety of himself and of other persons who may be affected by his acts or omissions at work.
This refers to the ICNIRP guidelines on exposure: - Wavelength dependency of the hazards - Maximum exposure for specific bands of emissions
The employer must eliminate or reduce any risk related to exposure to optical radiation. Staff exposure to non-coherent optical radiation must be below Exposure Limit Values (ELVs) specified in Annex I of the AORD.
The wavelength dependency of the optical hazard is described by hazard Action Spectra (AS). The ICNIRP adopts 2 spectra for UV, one for blue light damage and one for thermal damage.
$ MET = \frac{b}{E} $
MET is Maximum Exposure Time (s), b is the guideline limit (Jm-2), and E is the Exposure produced by the unit (mWm-2)
Non-laser optical equipment uses what time of radiation and what are the range of emissions?
Broadband radiation wth emissions between 100nm - 3mm
Name four typical non-laser optical sources in healthcare
Phototherapy UV lights, diagnostic lights, blue light units and infrared thermometry
Who is the body that advises on NIR hazards?
ICNIRP
What are the organs exposed to NIR optical radiation?
Skin and Eyes
What is the specific UK regulation on UV?
The Control of Artificial Optical Radiation at Works 2010 is the specific UK regulation