Core of Knowledge in Safe Use of Lasers & IPL’s in healthcare Mr John Saunderson, Consultant Medical Physicist

Why laser core of knowledge?

Core of Knowledge syllabus Understand the characteristics of optical radiation emitted from different types of equipment. Familiar with the intended purpose of the optical radiation equipment. Aware of the meaning of the warning labels associated with optical radiation equipment. The effects of exposure and health hazards, including eye, skin and tissue, which can arise from the use of laser, IPL or other optical radiation equipment. Equipment related hazards, which can arise from the use of laser, IPL or other optical radiation devices, including equipment malfunctions. Management of equipment and the role of personnel, including Controlled Areas and the role of the Laser Protection Adviser and Supervisor. The principles and requirements of equipment quality assurance processes and procedures. Hazards related to individuals through use of optical radiation equipment, including electrical hazards, fire risks and smoke plume effects. Hazards to patients associated with optical radiation treatment procedures and methods of minimising risks. Hazard control procedures, including the use of personal protection. Hazards from reflections or absorption of the optical radiation beam with respect to instruments or surfaces or other equipment. General principles of how to deal with a suspected accidental exposure to optical radiation. Aware of the basic principles of the maximum permissible exposure levels and the precautions required to ensure that exposure of unprotected skin and eyes of those present is less than the maximum permissible levels. Additional precautions that may be necessary when undertaking non-routine activities with the equipment. The safety procedures and policies governing optical radiation equipment use, including the local rules, Controlled Area, emergency action and accident reporting procedures. Understand the role of the Laser Protection Advisor and Laser Protection Supervisor. Be aware of the relevant legislation and standards that pertain to lasers and IPLs. Principles of risk assessment. Be familiar with the basic principles of the administration of safety.

Nature of Laser Radiation

L ight A mplification by the S timulated E mission of R adiation

Electromagnetic Spectrum

nm - red nm - orange nm - yellow nm - green nm - blue nm - indigo nm - violet

Light Sources & Lasers Spontaneous emission –filament lamp –fluorescent lamp –neon lights –most LEDs –fire –fluorescence –IPL (intense pulsed light source) Stimulated emission –laser

Spontaneous emission Atom

Energy (e.g. electrical current through filament, or electrical discharge through a fluorescent tube, or UV light on a fluorescent material)

Excited atom

Spontaneous emission Atom Photon emitted Any direction.

Spontaneous emission

Stimulated emission Atom

Energy (e.g. electrical discharge, flash lamp, electrical current)

Excited atom

Stimulated emission Incoming photon (correct wavelength)

Stimulated emission Two photons emitted IF correct wavelength then  STIMULATED EMISSION Same wavelength and same direction

Incoming photon (wrong wavelength)

Scattered photon

LASER Tube filled with laser medium (e.g. helium-neon gas for HeNe laser)

LASER Energy (e.g. electrical discharge, flash lamp, electrical current)

LASER Population Inversion or “pumping” Energy (e.g. electrical discharge, flash lamp, electrical current)

LASER Spontaneous emission takes place

LASER Some photons will cause stimulated emission

LASER Mirrors at either end reflect those photons travelling along tube

LASER More simulated emission in same direction along the tube

LASER Amplification

One mirror (output coupler) “leaky” allowing laser beam to emerge All photons same wavelength (colour) All photons travelling in same direction Can produced extremely short pulses of high energy

Non-coherent vs laser light source Extended vs point source 40 Watt incandescent bulb ~2% efficient  0.8 W = 800 mW light energy 1 mW laser pointer 800 x less light energy emitted than 40 W bulb

cm Irradiance, E = 800 ÷ (4  x ) E = mW/cm 2 Similar in all directions 1 mW pointer, 0.15cm beam diameter In most direction, E = 0 all distances In beam, E = 1 mW ÷ (  x ) E = 14 mW/cm 2 i.e. 2,300 x more than 40 W bulb Extended vs point source

Compared to 40 W 1 m (assuming 1.5 mm dia beam) 1 mW Laser pointer x 1 m 2W Pascal - 2 W x 1 m 40 W CO 2 laser x 1 m (Note, other effects make this even higher on retina)

Non-coherent vs laser light source Chromatic Aberration Lasers are “monochromatic” (single wavelength) so minimal “chromatic aberration”

Non-coherent vs laser light source Extended vs Point Sources Object / Source Image Lens

Image Object / Source Lens 1

Extended source

Image Object / Source Lens 2

Distance object Image  Object / Source Lens

Distance object Image  Object / Source Parallel rays, non divergence, “collimated” = virtual point source

All parallel beams will focus to about 20 microns (0.02 mm)

e.g. for 1 mW laser pointer E(skin) = 14 mW/cm 2 (from earlier) 1.5 mm beam focussed to 20 microns   (1.5/0.020) 2 =  5,600 power density  E(retina) = 70,000 mW/cm 2 (assuming 10% absorption in eye) So EYE is at much greater hazard than SKIN for wavelengths focussed by cornea & lens Eye is at greater hazard from LASERS than from other light sources (Lasers also more useful for creating a concentrated point source)

Intrabeam, specular reflections, diffuse reflections Intrabeam –directly shone into eye –if focussed by eye, 20  m spot on retina

Intrabeam Viewing If beam larger than pupil only proportion of beam will be focussed on retina If magnifying glass etc used a greater proportion will be focused on retina

Intrabeam Viewing If beam smaller than pupil diameter, magnifying glass make no difference to retina (would to skin)

Specular reflection = mirror-like reflection Potentially same hazard as direct intrabeam viewing

Diffuse Reflection e.g. seeing laser spot on wall Not a point source, –so not focussed to 20  m May still be hazardous

Lenses, mirrors & fibres All produce a divergent laser beam Lens Mirror Optical fibre

Lenses, mirrors & fibres Concave mirrors and convex lenses –focal spot - high irradiance –beam then gets broader –if bigger than pupil then hazard reduces with distance Optical fibre –diverges from exiting fibre –if bigger than pupil then hazard reduces with distance

Video 1

Types of Medical Laser

UV visible > < infrared

Taken from A Non-Binding Guide to the Artificial Optical Radiation Directive 2006/25/EC, Radiation Protection Division, Health Protection Agency

CO 2 laser IRA IRBIRC Nd:YAG laser 

CO 2 laser Nd:YAG laser  Argon laser  VIBGYORVIBGYOR KTP-Nd:YAG - frequency doubling to 532 nm (green)

UV visible > < infrared

Absorption of electromagnetic radiation in the eye (Sliney & Wolbarsht 1980)

__________________________ Continuous beam __ Single pulse __ __ __ __ __ __ __ Interrupted pulses

Laser Safety Classes

Video 2

Laser Device Classes & Hazards Class 1 Class 1M Class 2 Class 2M Class 3R Class 3B Class 4 Applies to device as a whole.

MPE = Maximum permissible exposure

Class 1 –no risk to eyes (including using optical viewing instruments) –no risk to skin –(either low power device or totally encased)

Class 1M –no risk to the naked eye –no risk to skin

Class 2 –no risk to eyes for short term exposure (including using optical viewing instruments) –no risk to skin –(visible, so blink response protects) –(may cause dazzle or flash blindness)

Class 2M –no risk to naked eye for short time exposure –no risk to skin

Class 3R –low risk to eyes –no risk to skin –(risk for intentional intrabeam viewing only) –(may be a dazzle hazard)

Class 3B –medium to high risk to eyes –low risk to skin –(aversion response protects skin, or must be focussed to such a small spot that pin-prick effect only)

Class 4 –high risk to eyes and skin –diffuse reflection may be hazardous –(possible fire hazard)

HEYH Trust CP137 Health & Safety at Work Policy - Lasers - Includes safety of class 3B and class 4 lasers

Safety Principles 1.Engineering e.g. doors, blinds 2.Systems of work e.g. Local Rules, warning signs, etc 3.Personal protective equipment (PPE) e.g. Laser safety eyewear

Risk Assessments

Laser Safety Structure Risk assessment Controlled Area Local Rules Laser Protection Supervisor Laser Protection Adviser Authorised Operators and Assistants

Controlled Area Must contain the risk Need to know nominal ocular hazard distance/zone (NOHD, or NOHZ) –i.e. distance where exposure level < MPE –e.g. Lithotripsy laser - 80 centimetres –e.g. Surgical CO metres Walls, blinds, doors (without gaps), etc. Lock doors unless can justify not Warning signs at every entrance

Local Rules (How to work safely in the Controlled Area) Specific to each laser What are hazards? Controlled area - limit area of hazard - signs Users & Laser Protection Supervisor Safety precautions (e.g. eyewear, blinds) Methods of safe working, etc. Adverse incident procedure, LPA, etc.

Warning Signs IONISING RADIATION (e.g. X-rays) UltravioletRF radiation Hazardous magnetic field LASER

Example

Laser Protection Supervisor

Laser Protection Adviser

Authorised Users

Incidents

MDA “One Liners” - Eye risk? August 2002 (Issue 17) MDA has become aware of the use of inappropriate filters for lasers used in ophthalmic surgery. This can lead to permanent eye damage for the operator.  When connecting a laser to a protective system with filters, ensure that the wavelengths of laser radiation for which the filter offer protection match the output wavelength of the laser. If a fault is suspected with the filters, the procedure should be discontinued and the filters examined by a trained engineer.

Example Laser nm Green, 2 W nm Yellow,  1 W 670 nm Red (aim), < 5 mW Goggles labelled nm OD> nm OD> nm OD>6

Example Laser nm Green, 2 W nm Yellow,  1 W 670 nm Red (aim), < 5 mW Goggles labelled nm OD> nm OD> nm OD>6

MDA “One Liners” - Hind Sight? March 2000 (Issue 8) Two separate incidents reported to MDA involving faulty laser equipment resulted in permanent retinal damage (one to a patient and one to the operator). In both cases, the operator had noticed that the equipment was behaving unusually but carried on with the procedure. Abnormal performance of any equipment should be questioned immediately.

Laser Safety Eyewear

Laser Eyewear Labelling DI 1060 L7 X Z 620 TO 700 nm OD 2 CARBON DIOXIDE, O.D NM DIR L4 D 1064 L7, IR 1064 L8, DIR L7, DIR > L5, DI L5, DI L5 D = continuous wave laser, I = pulsed laser (0.1 ms ms) R = giant pulsed laser (1 ns - 10  s), M = mode-coupled pulse laser (< 1 ns)

Wavelength Number before the L in nanometres “Colour” of beam May be single number (e.g ) or a range (e.g – 2100) Wavelength on laser should fall within range on eyewear

Optical Density Number after the L Strength of filter OD 1 – only 1 / 10 th of laser light transmitted OD2 - 1 / 100 th, OD3 - 1 / 1000 th, etc. Local rules should say strength required. Note – higher ODs may be very dark

Laser Safety Eyewear Must match the laser in use (whether specs or filter) Must be cleaned in accordance with manufacturer’s instructions If damaged, take out of service Consider protection of patient’s eyes

Other Hazards Fire Anaesthetic gas ignition Plumes Electrical hazard

Can be fatal

Electrical Hazard Big capacitor used to drive laser, so dangerous even when unplugged Several fatalities from lasers DON’T OPEN OR DISMANTLE LASER Don’t let anyone else do so unless they are suitably qualified and trained.

Plume Mostly steam, carbon particles, cellular products - average 0.3  m particles May contain formaldehyde, hydrogen cyanide, hydrocarbons, mutagens Human papilloma DNA identified in plume from surgery to remove of papillomas Use smoke extraction with filter (<0.1  m) (not hospital vacuum) Staff and patients should wear well-fitting high filtration face masks where plume hazard identified.

Odds and ends Maintenance Reflections of polished instruments Check fibre. Fibre breaks. Oxygen hazard.

And finally.... Example of laser accident Dr. C. David Decker Nd:YAG, 6mJ, 10 ns pulse Goggles available, but –Tunnel vision –Clouded up –Uncomfortable –So not worn Reflection beam hit eye Pop!

Goldman-Fields Scan of Dr Decker’s damaged eye 4 months after accident Damage under high- intensity illumination (red) Damage under low- intensity illumination (blue) Laser induced blind spots (pink) Optic nerve blind spot (orange)

f i n