4/15/20 OBJECTIVES 1. To provide a clinically relevant review of laser physics. 2. To introduce the two main lasers used in Laryngology. 3. To review settings and appropriate laser use. 4. To discuss their application to laryngeal pathology with special attention to dysplastic and early malignant laryngeal disease. CORONA Initiative 2020? Andrew Tkaczuk MD Emory School of Medicine Assistant Professor of Otolaryngology Division of Laryngology DISCLOSURES BOARD RELEVANCE Good references 1. Although I picture commercially available equipment, I have no financial interests Regarding lasers: in any of the companies. ● http:// 2. These are powerful instruments with tremendous clinical potential, but can cause • Much of the facts regarding lasers are www.entdev.uct.ac.za/ great herm to all involved. clinically relevant and are tested. guides/open-access-atlas-of- Regarding early glottic cancer: otolaryngology-head-neck- 3. I do provide my personal application of these devices, which may differ from your operative-surgery attending physicians. • Early glottic cancer tends to have a low in- service and written board yield. ● https://link.springer.com/ • More likely to have questions on path and book/ laser specifics than early glottic cancer 10.1007/978-981-10-5586- management 7 • HIGH oral board and HIGHer life yield and. ● Chapters 60 and 108 in Cummings. IT’S AN ACRONYM LASER HISTORY IN ORL Otologists were among the first to describe utilization of lasers in animal models. Light • Stahle and Hogberg were among the first to investigate the potential use of lasers in Otologic surgery. Used a ruby laser to carry Amplification (by) out inner ear surgery in pigeons. • J Sataloff used the neodynium:glass laser to vaporize isolated Stimulated human footplates. Microlaryngoscopy and laser technology almost developed in tandem. Emission (of) • Kleinsasser introduced microlaryngoscopy in the early 1960’s. • Jako in the US is heralded as among the first to describe the Radiation potential of lasers. 1 4/15/20 LASER HISTORY IN LARYNGOLOGY --LASER--* ANATOMY • In the early 1970s: CO2 laser is introduced to the world of surgery. • Endoscopic use to treat laryngeal papillomatosis and larynx cancer. • "Laser Surgery of the Vocal Cords: An Experimental Study With Carbon Dioxide Lasers on Dogs" (Laryngoscope. Geza Jako 1972;82:2204-2216). • Well, what makes a laser function. --LASER--* ANATOMY • A laser is a resonant cavity with a gain medium powered by an energy source. • Common among all lasers are: an energy source, an excitable medium [gas - COS, liquid - Dye, or solid state – potassium titanyl phosphate] Pumping mechanism – Energy source • Laser emission is dependent on the excitation of electrons (population inversion) where most of the material is excited. On relaxation the released photon can excite other atoms. Total Reflector Partial Reflector 1. The atoms and electrons within the lasing medium are excited by the power source 2. After excitation they return to a lower energy state releasing photons which in turn excite others. Output Beam 3. Photons of identical wavelengths are reflected in the optical chamber and due to reduced reflectivity of one of the mirrors the photons are transmitted 4. The emitted beam is focused by a lens Laser Medium 5. The mirrors continue to provide feed back to maintain the stimulated emission. This produces an intense beam of light. --LASER--* ANATOMY --LASER--* LET THERE BE LIGHT Pumping mechanism – Energy source Total Reflector Partial Reflector Output Beam Laser Medium • Well what makes this light special • As you know visible light is just a part of a larger electromagnetic spectrum. • Some of the lasers that we utilize clinically do not fall within the visible spectrum. • Using visible light as an example, what makes laser light different than the light we see emanating from our light bulbs? • The main properties are collimation, coherence, and monochromaticity. • From the lower diagram you can appreciate that the laser light is parallel (collimated), of a single wavelength (monochromatic), and in the same phase with a constant phase difference and periodicity spatial and temporally (coherent). 2 4/15/20 --LASER--* TISSUE INTERACTIONS Clinically and commercially lasers have effects based on their local tissue or material interactions. 1. Reflection – happens constantly within the laser and can happen with tissues as well, but more likely equipment. (No energy loss or tissue effects) OTOLARYNGOLOGY 2. Absorption – Which is the intended outcome and deposition of the energy at the tissue. (Energy loss) 3. Scatter – Which is incomplete deposition of the energy and represented in diffuse reflection and diffuse transmission in this image. (Energy Loss and deposition in tissue) Non-specific lasers like Nd- Yag have deeper optical depths due to less absorption. 4. Transmission – (No energy loss or tissue effects) • What happens at the tissue level is dependent on several factors, but among the most relevant to the laser itself is the wavelength. • Most tissues are optically opaque media, therefore scattering has to be taken into account. Scatter occurs at interfaces such as cell membranes, cell nuclei, etc. KTP • Absorption by tissue is frequently by chromophores such as melanin, hemoglobin, water. 532nm • This is the absorption spectrum for oxyhemoglobin and water, the major chromophores for the head and neck. • UV wave lengths shorter than 300 nm, the laser radiation is chiefly absorbed by cellular proteins and nucleic acids. --LASER--* VARIABLES • Visible light radiation and near-infrared (NIR) wavelengths (400-1200 nm) are absorbed mainly by Energy = Joules (J) chromophores • In the far-infrared range (>1200 nm) water is the most efficient absorber. Power = Energy/time ! Watts (W) = Joules (J) / second (s) • Scattering too varies with the wavelength. It is greatest at shorter wavelengths and steadily decreases Spot size : Fiber size ! Determined by focal length (focus) : distance from surface with increasing wavelength. This makes sense since a tighter wavelength has more opportunities to run into something. Irradiance or Power Density = Power/Area (Spot size) à W/cm2 • Capitalizing on absorption reduces scatter and reduces the spread of thermal energy. Exposure time : Continuous versus pulse (pulse width; pulses per second) Fluence = Energy/Area à J/cm2 3 4/15/20 KTP LASER CO2 LASER • The CO2 laser is a continuous wattage laser that can be set to a pulse mode as well as “Scanning” modes. • Power is similar set by the surgeon as Wattage, but tissue interaction again is dependent on the Irradiance (Power/area). • A continuous small spot sized focused laser will have a tremendous power density On the KTP laser which is a fiber based laser and classified as a photoangiolytic laser (Irradiance) and will have considerable vaporization. Again of our main settings: • On scanning modes with super pulse you adjust the spot size/shape and the pulse rate • Power is adjusted as Wattage and Irradiance will be determine by the Wattage and the (time off). Fiber size • While scanning, the laser is “painted” or “printed” in many energy bursts of high wattage • Area is based on the size of your fiber that average the wattage set over time. • Time is the the mode settings, most frequently used as pulsed. A pulse Width is the • Bursts allow tissue cooling and relaxation to reduce thermal damage. duration of the pulse and a pulse rate is the frequency. • Typical settings will be around 3 Watts continuous, sometimes less for fine cutting some • Typical settings for pulsed cases will be 26-30 Watts, 15-20 ms pulse widths, and 2-3 times more for thicker/dense tissue. pulses/sec. • 5-10 Watts on scan/SP. WHY PULSE? 1. Avoid resident iatrogenic damage. 2. Reduce energy dispersion by molecular relaxation. 3. Capitalize on the heat sink effect. 1. Chapter 60. Cummings 2. https://www.intechopen.com/books/high-energy-and-short-pulse-lasers/effects-of- different-laser-pulse-regimes-nanosecond-picosecond-and-femtosecond-on-the-ablation- Tatli S, et al. Radiofrequency ablation: technique and clinical applications. Diagn Interv of-ma Radiol 2012;18:508-516. --LASER--* TISSUE INTERACTIONS 4 4/15/20 • Laser tissue interactions depend on the wavelength of the laser light, the power and duration of a single pulse, the repetition rate, and the spot diameter. • These are all laser settings --LASER--* TISSUE INTERACTIONS • In this graph is the laser tissue interaction is depicted as power density of the laser vs the exposure time of the laser. • With lower energy deposition and increased duration there is not any photothermal effects but rather photodynamic effects, which produce reactive oxygen species • Coagulation is frequently • For a thermal effect to occur the light energy must be converted to heat. This is also dependent on wavelength and exposure time. • With longer exposure times heat builds and produces coagulation zones beyond the penetration depth of the wavelength. • Thermal effects may spread beyond the optical penetration depth. The active depth takes this into the account. • This is very dependent by the tissue properties such as heat conduction, capacity, and blood flow. There is the optical penetration depth. Chapter 60. Cummings Chapter 1. Lasers in Otorhinolaryngology --LASER--* TISSUE INTERACTIONS • Similarly to time your distance and more so focal length at that distance will effect the efficacy of your laser. • As can be seen here an unfocused laser (not 1:1) results in lower power density • A focused laser and again spot size all controlled for the same power can dramatically increase the amount of energy deposited. • Spoken in another way lower power and a defocused laser or large area is more likely to coagulate than vaporize as seen in this second graph. Chapter 60. Cummings Chapter 1. Lasers in Otorhinolaryngology • CO2 laser is great as well, but KTP LASER RRP for anterior disease, the vectors can become quite The obvious: Disadvantages/Considerations: difficult. § Fiber based § Less precise beam of light • For degrees of freedom of § Visible spectrum with § Higher depth of penetration difficult angles a hand piece is doubled frequency § Bulky disease beneficial.