Laser in Urology campbell urology .pptx

Laser

1. Laser in Urology Dr Nirmal Prasad Sah

2. L aser an acronym for “ l ight a mplification by s timulated e mission of electromagnetic r adiation.” In the 1980s lasers first became of interest to researchers and clinicians in urology E mployed to treat soft-tissue conditions such as urinary calculi, stricture disease, benign prostatic hyperplasia (BPH), urothelial cell cancer, and genital skin lesions

3. General components: an energy source : electrical current or a different wavelength of light an active medium: solid, liquid, or gas a resonant cavity: mirrors to reflect light, allowing it to have many passes through the medium Pumping : M ost of the atoms or molecules within the active medium brought simultaneously to a higher energy state by an energy source for laser action to occur

4. Specific properties of Laser light M onochromatic and of a single wavelength C oherent (all photons are in phase with one another), C oherent with a uniform spatial relationship between all portions of the electromagnetic wave C ollimated (photons travel parallel to each other), D irectionality with minimal divergence to maintain brightness over long distances H igh concentration of the bright laser light when focused on a small spot

5. Wavelength of Laser light A rgon (488 nm—blue; 514 nm—green) N eodymium: YAG (Nd:YAG; 1064 nm and 1318 nm) Ho:YAG (2100 nm) lasers

6. Pulsed and Continuous Wave Lasers Depending on how the excitation energy is applied and how the laser cavity configured, the output beam of laser light is either pulsed wave or continuous wave. Pulses delivered individually, in groups, or continuously over a wide range of frequencies A laser considered continuous wave if the output emission is greater than 0.25 second.

7. C ontinuous wave laser delivers output i.e continuous and of a constant amplitude allows for a stable, easy-to-control instrument P ulsed wave laser delivers bursts of energy, which works well for stone fragmentation more difficult to control during soft-tissue interactions

8. The power of the laser is equal to the energy over time (P = energy/time or W = Joules per second [J/sec]) , and a high degree of power reached with even a small amount of energy if very short pulses used Several techniques exist that can compress or shorten the pulse Examples: Q-switching and mode locking

9. Q-switching Involves interrupting the light beam in a controlled fashion so that the laser action delayed until maximal population inversion occurred in the active medium . It generates lower pulse repetition rates, higher pulse energy, and longer pulse Mode locking combined with Q-switching C reate ultrashort pulses by fixing the way photons bounce back and forth in the resonant cavity C reate very high power pulses because of their ultrashort duration

10. Delivery Systems F ixed rigid systems : articulating arms Flexible systems : fiberoptic glass fibers Fiberoptic systems are generally inexpensive and versatile; however, fiberoptic materials are unable to transmit all laser wavelengths E xample: C arbon dioxide (CO2) laser, with a wavelength of 10.6 μm , does not pass through quartz or glass fiber optics, and instead a more rigid system composed of an articulating arm with a series of mirrors employed needed

11. Light-Tissue Interaction Laser light absorbed by tissue in a wavelength-dependent fashion S ome of the light, independent of the wavelength, reflected by the boundary layer of the tissue and cause heating and collateral damage in the surrounding tissue The optical properties of the tissue and the surrounding irrigant affect the degree of reflection Because this process is not dependent on the wavelength, reflection often not considered when selecting a wavelength for surgical lasers

12. Scattering: Some scattering of the laser energy may also occur S ome of the intended laser energy is taken out of the surgical field The degree of scattering varies with the wavelength of the laser Typically, lasers with shorter wavelengths have a much greater amount of scatter compared with lasers of longer wavelengths

13. The most important light-tissue interaction: Absorption. When the laser beam enters into a medium in which it is absorbed, the intensity of the laser energy decreases in an exponential fashion consistent with Beer-Lambert law This law states that a logarithmic dependence exists between the transmission of light through a substance, the product of the absorption coefficient of the substance, and the distance the light travels through the material

14. Absorbed laser energy is converted to heat and increases the temperature of the target tissue If enough heat generated, coagulation and subsequently vaporization can occur A chromophore required for absorption to occur Example: melanin, hemoglobin, and water

15. Types of laser: Neodymium:Yttrium-Aluminum-Garnet W avelength of 1064 nm and tissue depth of penetration of about 1 cm. H emostatic and coagulative tissue properties Historically, U sed in urology for the treatment of BPH with visual laser ablation of the prostate (VLAP) and interstitial laser coagulation of the prostate

16. V isual laser ablation of the prostate (VLAP) S ide-firing laser fiber used to direct the laser beam at 60- to 90-degree angles The fiber held off the prostatic tissue, and an area of heat-induced coagulative necrosis produced as the tissue targeted. The coagulated tissue not entirely cleared at the time of surgery, but rather a sloughing process occurs in the weeks after surgery with associated edema Prolonged postoperative catheterization needed in 30% of individuals

17. I nterstitial laser coagulation of the prostate Involves placing laser-diffusing fibers directly into the adenoma of the prostate P erformed either transurethrally or via a perineal approach. Similar to VLAP, the tissue undergoes coagulative necrosis and subsequently atrophies Prolonged periods of catheterization after surgery—often 7 to 21 days —because of the high risk of urinary retention

18. Published retreatment rates of up to 20% at 2 years and 50% at 54 months suggest poor long-term durability ( Daehlin and Frugard , 2007 ; Perlmutter and Muschter , 1998 ). With the advent of newer laser technology and techniques, the use of the Nd:YAG laser for BPH largely been abandoned.

19. Potassium Titanyl Phosphate “ green light ” laser, frequency-doubled Nd:YAG laser. The Nd:YAG laser beam passed through a KTP crystal, results in doubling of the frequency and halves the wavelength to 532 nm S trongly absorbed by hemoglobin and in well-vascularized tissue only 1 to 2 mm of tissue penetration Photoselective vaporization of the prostate (PVP) in which the well-vascularized prostate tissue treated in a noncontact fashion with a side-firing laser fiber The targeted tissue quickly increases in temperature above the boiling point and vaporized leaving behind a rim of coagulated tissue that provides a layer of hemostasis .

20. In contrast to VLAP, the limited depth of tissue penetration results in less tissue edema, and prolonged catheterization usually not required The early KTP laser systems: low-powered 34-W systems and were used in conjunction with a standard Nd:YAG laser A hybrid surgical technique: VLAP with the Nd:YAG laser and then used the KTP laser to perform bladder neck incisions R educe the prolonged catheterization and bothersome postoperative lower urinary tract symptoms after standard VLAP

21. H igher-powered 60-W KTP laser: performed independently of the standard Nd:YAG laser. Development of an 80-W and a 120-W KTP laser More recently, a 180-W GreenLight XPS laser been shown to be more favorable compared with the 120-W laser with regard to reduced operative time, fiber use, and PSA-reduction, suggesting more cost-effective and efficient tissue removal

22. Lithium Triborate 532-nm wavelength laser 120-W lithium triborate (LBO) laser was developed to increase the efficiency of the tissue vaporization compared with the 80-W KTP laser The higher power allows the distance between the fiber tip and the target prostate tissue to be increased to 3.0 mm versus 0.5 mm for the KTP laser The greater distance may help preserve the laser fiber and make it technically easier to use. hemostasis with the higher-powered system appears to be less compared with the 80-W system

23. A steeper learning curve has been reported with the 180-W systems, with up to 120 procedures needed to work through the process and handle the higher power of the system safely and effectively

24. Diode W avelengths of 808 to 980 nm B ehave similarly to Nd:YAG lasers M uch more efficient than the Nd:YAG and requires only a standard wall plug for operation P rovide better hemostasis compared with the LBO laser higher complication rate; postoperative frequency, urgency and epididymitis considered as safe and effective as monopolar TURP at 3-month follow-up

25. advantage of shorter hospitalization and catheter indwelling times and no need for discontinuation of anticoagulant therapy ( Cetinkaya et al., 2015 ) demonstrated that improved symptom scores, maximum flow rate, and postvoid residual urine observed at 24 weeks remained virtually unchanged at 1 and 2 years ( Miyazaki et al., 2017 ).

26. Holmium:YAG 2140-nm pulsed laser S trongly absorbed in water, traveling only about 0.5 mm in the fluid medium, making it ideal for the urologic environment In the prostate, the absorption depth is about 0.4 mm, resulting in a high-energy density that leads to the rapid vaporization of tissue Heat also generated during this process and allows for coagulation of small blood vessels up to a depth of approximately 2 mm.

27. Mechanism: The onset of vaporization occurs in the irrigant adjacent to the tip of the laser fiber With each pulse of the laser, a steam bubble of a few millimeters in diameter created The bubble not visible because it is present for only about 500 μsec —about the same length of time as the laser pulse duration

28. Holmium laser enucleation of the prostate ( HoLEP ) L aser pulses create the steam bubbles, which lead to the separation of the prostatic adenoma from the capsule of the prostate Tissue vaporization occurs and leads to the white fibrous appearance of the tissue The heat generated during the process allows for hemostasis to occur in the adjacent tissue For persistently bleeding vessels, the laser can be “ defocused ” by increasing the distance between the fiber tip and the target bleeding vessel; this results in only the coagulation effect occurring with limited or no vaporization.

29. R elatively easy procedure to learn but did require a high-powered Ho:YAG laser (80 to 100 W) and a side-firing laser fiber T he rate of vaporization was slow, and long procedure times were needed to treat men with large prostates adequately The side-firing fibers would also fail if held too closely to the tissue , likely because of thermal breakdown

30. HoLEP M edian and two lateral lobes are enucleated and pushed into the bladder in a manner mimicking an open prostatectomy T issue morcellator streamlined this process, and although still carries risk of bladder injury, it would appear to be much safer than using a transurethral resection loop P erformed in an almost bloodless field as a result of the coagulation produced by the Ho:YAG wavelength but also as a result of the extensive blunt dissection from the tip of the endoscope, similar to the use of a surgeon’s finger during an open retropubic prostatectomy E ffective for a broad range of prostate sizes and can be performed in men on anticoagulation A doption of HoLEP been slowed by the steep learning

31. H igher-powered Ho:YAG lasers (100-W, 120-W) used for stone lithotripsy allow for higher-frequency settings at lower pulse energies longer laser pulse duration provided effective stone comminution with the advantage of reducing laser fiber tip degradation and stone retropulsion ( Emiliani et al., 2017 ; Wollin et al., 2017 ).

32. Lumenis ( Yokneam , Israel) has developed a new technology for their Lumenis Pulse 120H laser dubbed the “ Moses effect ” The laser pulse imodulated to first separate the water then deliver the remaining energy to the stone, thereby reducing energy loss and improving fragmentation while reducing stone retropulsion. The technology requires use of their special Moses laser fibers. In a preclinical study, the use of the Moses technology resulted in significantly reduced retropulsion (stone movement was reduced by 50 times ) and more efficient laser lithotripsy

33. H olmium laser resection of the prostate ( HoLRP ) This technique involved cutting pieces of the prostate off as it was resected, similar to a TURP T he sizes of the pieces could be larger than typical TURP chips but had to be small enough to be able to irrigate them out of the bladder at the completion of the resection. M ore challenging than holmium laser ablation of the prostate and remained time-consuming in patients with large prostates

34. Thulium:YAG C ontinuous wave laser operating at a wavelength of approximately 2000 nm D iffers from the Ho:YAG laser in that the thulium ions are excited by high-power laser diodes instead of flashlamp excitation as in the Ho:YAG. L ess heat generation and increased power efficiency by a factor of five with the Thu:YAG laser, and no special electrical installation is needed to operate the laser S lightly less depth of tissue penetration. C ontinuous wave output promotes more of a direct cutting action of the laser versus tissue tearing and splattering with the pulsed output of the Ho:YAG

35. As the tissue is cut with the Thu:YAG , a seam of coagulated tissue is created and produces hemostasis. Hybrid techniques involving vaporization and resection ( vaporesection ) were developed and shown to be effective Thulium laser enucleation of the prostate followed and was demonstrated to have results similar to HoLEP In stone lithotripsy, there appears to be very little stone retropulsion with the Thu:YAG laser, even at higher energy settings (8 J)

36. Carbon Dioxide W avelength of 9.4 to 10.6 μm . strongly absorbed by water and used for numerous medical purposes including dermatologic applications. C ontinuous wave laser and highly efficient with a ratio of output power to pump power of 20%. In urology, used to treat skin lesions such as condyloma and penile carcinoma when an organ-preserving strategy employed

37. Laser Lithotripsy Lasers are named after the medium that generates their specific wavelength of light; for example, the laser was developed in 1960 and the first medium used was the ruby Could effectively fragment urinary calculi, this continuous-wave laser simply heats the stone until vaporization occurs, which requires the laser to generate heat greater than the melting point of the stone G enerated excessive heat and was not appropriate for clinical use

38. P ulsed lasers application of pulsed energy results in high-power density at the stone’s surface but little heat dissipation F irst widely available laser lithotrite was the pulsed-dye laser , which employed a coumarin green dye as the liquid laser medium. D rawbacks to coumarin technology: S tones of certain composition (calcium oxalate monohydrate, cystine) not fragment well or even at all T oxic agent and required cumbersome disposal procedures; Required eye protection made visualization of the stone and fiber difficult.

39. H olmium:YAG laser in lithotripsy S olid-state laser Pulse duration of the holmium laser ranges from 250 to 350 microseconds H ighly absorbed by water; because tissues are composed mainly of water, the majority of the holmium laser energy absorbed superficially, which results in superficial cutting or ablation The zone of thermal injury associated with laser ablation ranges from 0.5 to 1.0 mm

40. M echanism of stone fragmentation: The long holmium:YAG pulse duration produces an elongated cavitation bubble that generates only a weak shock wave, in contradistinction to the strong shock wave produced by short-pulse lasers. lithotripsy occurs primarily through a photothermal mechanism that causes stone vaporization Advantages: T ransmit its energy through a flexible fiber, which facilitates intracorporeal lithotripsy throughout the entire collecting system. S afely activated at a distance of 0.5 to 1 mm from the ureteral wall.

41. The ability of the holmium laser to fragment all stones regardless of composition is a clear advantage over the coumarin pulsed-dye laser. S afest, most effective, and most versatile intracorporeal lithotripters P roduction of significantly smaller fragments compared with other lithotrites - reduces the need for extraction of the fragments with basket or grasping devices P roduces a weak shock wave, which reduces the likelihood of retropulsion of the stone or stone fragments R equired eye protection for the holmium laser does not compromise the ureteroscopic view of the stone or the fiber

42. U se of energy levels applied for stone disease (i.e., less than 15 W), the operator’s cornea would be damaged only if it were positioned at a distance of 10 cm or less from the fiber Used to treat patients with benign prostatic hyperplasia, strictures, and urothelial tumors . Disadvantage I nitial high cost of the device and the cost of the laser fibers

43. Technique S traightforward and involves placement of the fiber on the stone surface before the laser is activated. Clear vision essential at all times to ensure the fiber maintains near contact to the stone After initiation of holmium laser lithotripsy, a short pause is often required because of the “ snowstorm effect ” created by the scattering of minute stone fragments, which can be cleared by endoscopic irrigation Caution must be exercised in operating the holmium laser near a guidewire or a basket because the holmium laser capable of cutting through metal

44. laser fiber should extend at least 2 mm beyond the tip of the endoscope t o avoid destroying the lens system or the working channel of the endoscope baskets used to stabilize calculi during laser lithotripsy should be composed of nitinol rather than stainless steel available in a variety of sizes, generally ranging from 200-, 365-, 550-, and 1000- μm diameters as well as end- or side-firing fibers only the 200- and 365-μm fibers are used for flexible intracorporeal lithotripsy, as larger fibers cannot be accommodated in an endoscope’s working channel.

45. Altering the treatment parameters affected the efficiency of fragmentation and risk of retropulsion. For example , low pulse energy (0.2 J) led to smaller fragments and less retropulsion at the cost of fragmentation efficiency L onger laser pulse duration (700 μ s or 1500 μ s) as compared with a traditional pulse duration (300 μ s or 350 μ s) provide effective stone comminution while reducing laser fiber tip degradation and stone retropulsion. To maximize efficiency of Holmium laser lithotripsy, shorter pulse durations with higher pulse energy has been recommended

46. Laser Lithotripsy Approaches Fragmentation and Extraction: S tones were broken into fragments and then retrieved from the kidney with basket devices. U reteral access sheath used to facilitate repeated passages of the ureteroscope as the fragments were extracted C ombination energy settings such as 0.6 to 1.0 J along with rates of 6 to 10 Hz N ot only maximizes laser tip preservation but also minimizes retropulsion or stone movement during lithotripsy Stone composition may direct metabolic intervention to help prevent future stone episodes

47. Dusting: P ulse rates of 50 Hz on 100-watt Holmium lasers R elied on lower pulse energy and higher pulse frequencies to fragment the stone into fine debris that could be left in situ in the kidney and then spontaneously be expelled by the patient. A ssociated with shorter operative times because of omission of active fragment retrieval B asket-associated complications can be reduced

48. G reater scope longevity with this approach L ow-power lasers - 15 or 20 Hz may be upper limit H igher-power lasers ( 100-watt laser)-of 50 Hz or even higher may be achieved The technique of dusting involves moving the laser fiber tangentially from the very edge of the stone and taking care not to break off large fragments from the main stone

49. K eep the laser fiber slightly off of the stone, which “ defocuses ” it and minimizes the mechanical acoustic effect of the laser energy At the beginning of the case, the laser energy typically less than the mass of the stone and the stone does not tend to move very much and stays in place. Once the stone is ablated down to a smaller mass, the laser energy becomes greater than the stone fragment and the stone will start to bounce within the calyx, making it more difficult to shave the stone from the edges When this happens, one can either extract the remaining pieces or place the laser fiber safely in the middle of the calyx and keep discharging the laser as fragments come into contact with the fiber—a technique known as “ popcorning

50. P opcorning P opcorning” uses the photoacoustic and the photothermal mechanisms of laser lithotripsy Longer pulse duration produces greater photothermal functionality Longer pulse duration reduces stone retropulsion and fiber tip degradation , with similar stone fragmentation rates compared with shorter pulse duration 1.0 J and 20 Hz as giving the most efficient fragmentation when using this technique ( Chawla et al., 2008 ).

51. Pulse duration is inversely related to power and can manipulate stone motion depending on the circumstance; this can be helpful in difficult-to-reach anatomy (i.e., lower pole stones) or when numerous fragments exist in a confined area (i.e., minor calyx) The fiber tip is placed several millimeters away from the stones (and mucosa), and shockwaves produced by vapor bubbles collapsing cause stones to bounce like popcorn Fragments may be deemed small enough to pass when they are of 1 to 2 mm The most commonly used technique to measure stone size: a guidewire or laser fiber

52. Erbium:YAG Laser Lithotripsy As a result of the relatively long pulse rate (250 to 350 μsec ), the Ho:YAG laser is considerably less efficient than other shorter pulse lasers. E rbium (Er):YAG lasers have a shorter pulse duration and longer wavelength ( 2940 μm ), they can still produce small fragments, but with improved efficiency over Ho:YAG lithotripsy Er:YAG laser forms a t orpedo-shaped vapor bubble in the interfacing fluid between probe and stone Ho:YAG laser is pear shaped , leading to increased energy loss laterally, producing weak shockwaves with minimal effect on stone fracture.

53. A combination of effective photothermal and photoacoustic lithotripsy of Er:YAG leads to faster fragmentation, with larger subsequent pieces. Soft tissue depth of penetration is 0.79 μm , which is a significant improvement in safety compared with Ho: YAG (0.5 to 1 mm) . A problem with Er:YAG laser technology is that the hydroxy silica quartz fibers used in Ho:YAG machines are not compatible . S apphire fibers used with Er:YAG are too brittle and thick to be used in routine endourologic procedures

54. Thulium fibre in lithotripsy Advantage over holmium: Laser fibers are smaller, which may permit improved endoscope deflection and irrigation flow

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