Biophysical Basis of Optical Radiation Exposure Limits. Bruce E. Stuck

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1 Biophysical Basis of Optical Radiation Exposure Limits Bruce E. Stuck ICNIRP Member ICNIRP 8 th International Radiation Workshop Cape Town International Conference Center Cape Town, South Africa May 9-11, Bruce E. Stuck

2 Biophysical Basis of Optical Radiation Exposure Limits Summary: ICNIRP Optical Radiation Exposure Limits ICNIRP Radiation Exposure Limit (EL) Guidelines for CIE Optical Radiation Spectral Regions: UVC( nm), UVB ( nm), UVA( nm), Visible ( nm), IRA ( nm), IRB ( mm), IRC (3 mm mm) or 3000 THz 300 GHZ. Latest Optical Radiation Updates: Published in Health Physics Journal in 2013 Rationale Important References Laser and Broadband Available free at the ICNIRP Web Site: under the Publications Tab Statements and ICNIRP Blue Books also available Bruce E. Stuck

3 Wavelength Absorption How effectively light is captured by a target tissue Transmission How effectively light penetrates overlying media to reach the target tissue Slide courtesy of Professor M. Mainster

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5 Laser Emission Characteristics Emission Wavelengths Near ultraviolet to the far infrared Usually highly monochromatic (single wavelength or color) Emission Durations Single pulses as short as 10 femtoseconds (10-14 seconds) Continuous wave (CW) Repetitive pulses - Pulse repetition frequencies (single pulse to 10 8 pps) Beam Divergence Small beam divergence ( milliradian) or not. 0.5 mradian divergence - 50 cm beam diameter at 1 km Retinal Hazard Region: retinal irradiance diameter can be 30 micrometers or slightly less Irradiance Diameters ( Spot Size ) small (25 mm) to large

6 Dose Response Models Wavelength Ophthalmoscopy Temperature-Time Histories Exposure Duration Angiography Arrhenius analysis Radiant Exposure Pathology Peak temperature Irradiance diameter Electrophysiology Mechanism(s) of injury Exposure Site Visual Function Pulse Repetition Imaging (OCT,SLO) Frequency (PRF) Proteomics/Genomics Skin: Erythema - Blister Time of Observation (1 hr, 24 hrs, days, years?)

7 Ocular Effects 9-11 May 2016 Bruce E. Stuck

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9 Factors affecting Laser-Induced Retinal Injury and Laser Dazzle (Glare/Flash)

10 Thank You! Courtesy of Professor Martin Mainster

11 Collimated Laser Beam Focused onto Retina Cornea Aqueous Lens The retinal pigment epithelium (RPE) is a single layer of cells containing highly absorbing melanin granules. Most of the incident radiation is absorbed in a 5 mm layer of granules Vitreous Retina Sensory Retina RPE Choroid Slide courtesy of B.J. Lund and D.J Lund

12 Measuring Retinal Injury Threshold Reference Detector Eye Laser Shutter Wedge Attenuating Filters Mirror NHP eye Surgical level anesthesia Retrobulbar block Marker lesions define grid Dose varied site-to-site 9-11 May 2016 Fundus Camera Evaluate at 1 hr, 24 hrs Fundus Photography Direct Ophthalmoscope Response = Any detectable change Bruce E. Stuck

13 Measuring Retinal Injury Threshold Probit Analysis Log-normal distribution Threshold = ED 50 Dose 50% probability of producing retinal response Reported as irradiance, radiant exposure, or pulse energy (TIE) incident to cornea Also report 95% CL 9-11 May 2016 Bruce E. Stuck

14 Wavelength Dependence of ED 50 Data ns exposure 100 ms exposure Courtesy of B.J. Lund and D.J. Lund. Bruce E. Stuck

15 Burn/Lesion Laser Bioeffects and Dose Confined hemorrhage Vitreous hemorrhage Slide courtesy of D.J. Lund Bruce E. Stuck

16 Retinal Effect vs. Dose D.J. Lund Bruce E. Stuck

17 Laser-Induced Retinal Hemorrhage Thresholds Compared to the Minimum Visible Lesion Thresholds ED 50 - mj l 1Hr 24Hr Hemor Exposure Duration: 3.5 ns TIE - J W A V E L E N G T H - n m 430 nm

18 Corneal Lesions at 1.3 mm

19 Optical Radiation Effects a 1315 nm Bruce E. Stuck 19

20 Corneal Thresholds Dependence on Irradiance Diameter CO2 laser radiation at 10.6 m. Bargeron et al., Health Physics 1989 a c b

21 A. Corneal injury thresholds for short pulses and water absorption B. Corneal lesion 10.6 mm, 100 msec C. Porcine skin - one hour after exposure at 10.6 mm D. Porcine skin - 24 hours after exposure 10.6 mm B Infrared Laser Bioeffects RADIANT EXPOSURE (J/cm 2 ) 1000 C A WAVELENGTH ( m) hour 95%ABSORPTION DEPTH - (mm) D 24 hour

22 10000 Infrared Exposure Guidelines and Corneal and Skin Injury Thresholds (Not corrected for irradiance diameter) 1000 Radiant Exposure (J/cm 2 ) MPE( um) LAIR 1 JHUAPL TASC SRI 0.1 JHUAPL 2 um Gullberg et al - Blink Campbell et al GHz - NHRC 35 GHz - NHRC Skin-erythema Skin - blister/"spoty white" burn 1E-09 1E-08 1E-07 1E Exposure Duration (seconds)

23 Summary ICNIRP optical radiation guidelines are supported by a robust laser bioeffects data base Animal and Cellular Models Computational Models with understanding of light-tissue interaction mechanisms Some comparisons with human injury thresholds Interaction mechanisms Photochemical Photothermal Microcavitation around melanosomes Dose-Response Relationships Wavelength, Exposure Duration, Irradiance Diameter (Spot size), and Repetitive Pulses, Data requirements, issues or gaps - identified for the ICNIRP PG