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LASERS IN UROLOGY

Light Amplification by the Stimulated Emission of Radiation

ANATOMY OF LASERCOMPONENTSResonator Box (Glass/Ceramic tube) having 2 mirrors at opposite end.

Excitable medium [Lasing medium] (Solid, Liquid or Gas)

External energy source (Electronic, chemical, light)

What is stimulated emission?

LIGHT amplification

3 PropertiesMonochromatic (single wavelength, hence allows it to target specific chromophores)

Coherent (in phase, with respect to both time and space)

Collimated (emitted as a narrow, intense beam of light in parallel fashion to achieve its propagation across long distances without light divergence or loss of intensity)

LASER DELIVERY SYSTEM

Physical principles of laser action

ChromophoresChemical groups capable of absorbing light at a particular frequency and thereby imparting colour to a molecule.

Endogenous chromophores are: Melanin, Blood (Hb),water.ChromophoreWavelength absorbed (nm)Melanin700-1000Oxyhemoglobin415, 542, 577WaterAbove 1100-2940; 10600

biophysics of laser-tissue interactions

PARAMETERS OF LASER LIGHTEnergy describes the amount of work accomplished (joules).

Power refers to the rate of energy expenditure, measured in joules per second, or watts (1 J/s = 1 W).

Total energy applied to a given tissue is a function of the power multiplied by the duration of time the tissue is exposed.

Extinction length:

defines the depth of tissue up to which 90% of the incident laser beam is absorbed and converted into heat. Irradiance is a term used to describe the intensity of a laser beam, measured in watts per square centimeter.inversely proportional to the square of the spot size radius.

Spot size (mm): Larger the spot size, less is the scattering and deeper is the penetration of pulse.

The fluence (power density): amount of energy delivered per unit area (J/cm2)more important in determining a laser's effect on tissues than total energy delivered.

Pulse duration: Amount of time for which laser energy is applied

Pulse frequency(Hz): Repetition rate of pulse

Energy depositioncylindrical-shaped volume, which has the height of the laser beams extinction length and the approximate diameter of the laser fiber.

The density of the absorbed energy determines the effect of the laser on tissue.

Fluencedistribution of optical energy per unit volume within water or tissue.

Low fluence: Coagulation necrosis.High fluence: Vaporization effect.

Photothermal effect

Most commonly used effect of LASER in Urology.Energy absorbed and transformed into heat causes vaporization.Eg. Ho:YAG lithotripsy.KTP prostate photovaporisation.

Photomechanical / Acoustic effect

Cavitation bubbles

Plasma formationMechanismPhotothermalPhotomechanicalLasersHolmium, erbium,thulium, diode,Nd:YAG, KTPFREDDY, dye lasersAdvantages-Small fragments-All stone types-Minimal retropulsion-Cheap-No direct contact needed-Effective-Safe for tissuesDisadvantages-Collateral damage-Longer litho times-Requires direct contact-Ineffective for hard stones-Large fragments-More retropulsionPhotochemical effect

Admin. of photosensitive dye preferentially taken up by certain tissues.Admin. light of appropriate wavelength absorbed by dye to cause tissue damage/ablation.

Eg. Photodynamic therapy for superficial TCCTissue-welding effectFocusing light of a particular wavelength to induce collagen cross-linking.

Proteinaceous materials (eg, 50% human albumin, also known as tissue solder) directly to the tissue edges to be weldedor a chromophore that absorbs at the laser's wavelengthTYPES OF LASER

LASER OUTPUT MODEContinuous wave (CW): The output of the laser is continuous and of constant amplitude. The clinical effect is a more controlled interaction with the tissue.

Pulsed wave (PW) : PW delivers forceful bursts of laser energy, which is useful for stone fragmentation.

Lasing Media

SAFETY DURING USEAccidental firesTo minimize these risks,

Oxygen, if present, should be minimized;

Saline-soaked drapes or cloths should be used intraoperatively;

Alcohol-based skin preparations should be strictly avoidedEye protectionAppropriate eyewear is necessary for both patients and operating personnel.

Permanent visual loss can result from even minor direct retinal exposure to laser light.

laser lithotripsyGoal of laser lithotripsy:stone fragmentation with minimal surrounding tissue injury

Laser Used are:Pulse dye laser (PDL)Alexandrite laserFREDDY (Frequency-Doubled Double-Pulse Nd:YAG)Holmium:YAGErbium:YAG PHOTO MECHANICAL PRINCIPLEPulse dye laser (PDL)lasing medium is an organic liquid dye.wavelength emitted depends on the type of dye used, which can be changed or adjusted(Tunable).most common dye used is coumarin: 504 nmPulsed mode: Used for lithotripsy and ablation of vascular lesions.Alexandrite laserchromium-doped mineral [alexandrite (BeAl204)]wavelength range: 380-830 nm (tunable)light is absorbed well by melanin.Use:cutaneous lesions. lithotripsy of pigmented stones.Tissue wielding.

FREDDY (Frequency-Doubled Double-Pulse Nd:YAG)short-pulsed (Q-switched), double-frequency solid-state laser.2 wavelengths at 532 and 1,064 nm.Incorporating a KTP crystal into the resonator of a Nd:YAGUnable to break hard stones (cystine, COM, brushite).

PHOTOVAPORIZATIONHolmium:YAGholmium doped in a YAG crystal.2150 nm.Pulsed mode: energy is absorbed in the first 0.4 mm of substrate.

MechanismIn contrast to short-pulsed duration lasers: long pulse durations of 250 to 350 usec.

optical energy is deposited into water slowly

Weak bubble collapse induced acoustic effect.

Works on photovaporization.Fibre size200-micron: RIRS

365-micron: ureteral stones

550 and 1000 micron: Bladder & renal calculi

Setting200, 365 micron fibres: (end firing) < 1.0 J and 5 to 10 Hz.Start with 0.6 J & 6 Hz.

Large fibres (550,1000 microns): (side firing)Can be maximized to 2.0 J and 15 Hz.

LASERS IN BPENd:YAG laserNeodymium : yttrium-aluminum-garnet1064 nmIt has a long extinction length and penetrates tissue by approximately 4-18 mm, making it suitable for haemostasis and tissue coagulation.

TechniquesVisual laser ablation of the prostate (VLAP)

Contact laser prostatectomy

Interstitial laser prostatectomy (ILP)

Visual laser ablation of the prostate (VLAP)Side firing system Non contact modemirror to reflect or prism to refract the laser at various angles Coagulation with subsequent necrosis.

Contact laser prostatectomy

Sapphire tips are fixed to the fiber end to absorb energy and become very hot, which in turn allows tissue cutting by vaporization.Adv: Than VLAP, allowing immediate removal of tissue. Disadv: less hemostatic, slower, and inefficient for glands > 40 grams.

Interstitial laser prostatectomy (ILP) Transurethral placement of laser fiber directly into the prostate.

Produces a zone of coagulative necrosis some distance from prostatic urethta.

Adv: Less dysuria.

Greenlight/Photoselective vaporization of the prostate (PVP).kalium titanyl phosphate (KTP)

Nd:YAG laser pass through a KTP crystal.

Doubles the frequency halves the emitted wavelength to 532nm.

MechanismPenetration 0.1-0.4mm.Strongly absorbed by hemoglobin. Prostate tissue vaporization so no tissue for HPE. KTP energy poorly absorbed by water/saline. Non-contact vaporization possible.

Setting80 watts to 180 watts for vaporization;

20-30 watts for coagulation

Advantages:Less heating of the delivery fiber. Longer duration use. Laser heat concentrated over a small area with rapid tissue vaporization and minimal coagulation of underlying structures. Effective hemostasis so can be used for larger prostates (>100mL) and higher risk patients on anticoagulants.

Holmium Laser Therapyof the Prostatepulsed, wavelength of 2140 nm, Absorbed strongly by waterdepth of penetration is 0.4 mmPrinciplesPhotovaporization

vaporization without a deep coagulation zone when used with a side-firing fiber, a precise incision and enucleation while maintaining hemostasis when used with an end-firing fiber.

Holmium laser bladderneck incision (HoBNI)suited to small glands with an elevated bladder neck and short prostatic urethra.

Catheter-free outpatient procedure.Holmium laser ablation of the prostate (HoLAP)-199480100-W holmium laser generator 550-m side-firing fibre.2 J and 50 Hz/ 3.2 J and 30 Hz.Without the need for any tissue retrieval instruments.General or regional anesthesia NS as irrigant.

Vaporization of the prostate usually starts at the bladder neck using the side-firing laser fiber to make a BNI at 5 and 7 oclock; then the laser fiber is gently moved over the surface of the obstructed lobe towards the apex of the prostate proximal to the verumontanum.The end-point of the laser procedure is a TURP-like cavity lined by capsular fibers.Vs TURPvaporization techniques are best suited to small or moderate sized prostates.

Disadvantages:Costlier & log operative time in large prostate.No tissue for HPE.

Holmium laser resection of the prostate (HoLRP)similar to TURP. resected pieces were small enough to be retrieved Ellik evacuator.

Disadv: Long duration for large prostate.

Holmium laser enucleation of the prostate (HoLEP)persistent interest as the new gold standard for the surgical management of BPH in prostates of any size, replacing open prostatectomy and TURP.

TechniquesModified 26F continuous flow resectoscope sheath through which 5F or 7F catheters are introduced to hold and stabilize the end-firing laser fiber.Pulsed 80100-W holmium laser unit.550-m end-firing fiber. 2 J and 4050 Hz.NS as irrigant.Morcellator required.

STEP-A: INITIAL INCISION

STEP-B: TRANSVERSE INCISION FOR MEDIAN LOBE ENUCLEATION

STEP-C: UPWARD ENUCLEATION OF BOTH LATERAL LOBE.

STEPS-D & E: DOWNWARD ENUCLEATION OF BOTH LATERAL LOBES.

STEPS-F & G: COMPLETION OF LATERAL LOBE ENUCLEATION.

Thulium lasersRevolix laser110 W diode pumped, continous wave thulium:YAG laser980 nm diode laserGood absorption by hemoglobin AND water.Theoretically good hemostasis AND tissue ablationSmall, portable, easy to maintain, 110V power source

Advantage Vs Ho:YAGcontinuous-wave output. Shorter wavelength, the depth of penetration is decreased to 250 m. wavelength is close to the absorption peak of water and, together with the short penetration depth, this results in a high-energy density.Rapid vaporisation of water and tissue, Instead of the tearing action on tissue caused by the pulsed emission of Ho:YAG, the continuous-wave output of Tm:YAG allows smooth incision and vaporisation of tissue with excellent haemostasis.Disadvantage Vs Ho:YAGCW-output, cant do lithotripsy.TechniquesTm:YAG vaporisation of the prostate (ThuVAP): Destruction

Tm:YAG vaporesection (ThuVARP): Resection into small tissue chips (to be washed out)

Tm:YAG vapoenucleation (ThuVEP): Enucleation in combination with vaporization of the median and lateral lobe

Tm:YAG laser enucleation of the prostate (ThuLEP): Blunt enucleation with laser supportLASERS IN BLADDER TUMORLaser ablationNd:YAG tumor ablation.Principle: Coagulation necrosisAblation of tumors up to 2.5 cm in size. Techniques:60 W power output, noncontact straight firing fibre.20-30 watts for 2 seconds (safe)Indications: Small, low-grade, recurrent tumors.Palliative solution in unfit pt. for radical surgeryLaser excisionHolmium/Thulium lasers

Optimal indication: small tumour located at the trigonum, lateral bladder wall, or bladder neck.

Comparable to TUR. However, at present, there are no larger studies able to provide reliable long-term equivalence. [EAU-14]Photodynamic therapy (PDT)TCC of the bladder, either CIS orrecurrent superficial lesions unaffected by BCGPhotosensitizing agent:porfimer sodium (Photofrin) systemicallyor hexaminolevulinate (HAL) intravesically2-3 days after intravesical 630nm red laser light for 12-20 min.Laser-assisted partial nephrectomyPreliminary results indicate that laser-assisted laparoscopic PN without the need for hilar clamping is feasible.No major complication has been reported in humans.Promising alternative in renal surgery, which is worth further evaluation in clinical trials.

Laser-assisted laparoscopic nerve-sparing radical prostatectomy (LNSRP)Preliminary results indicate that laser-assisted LNSRP is feasible and could possibly enhance neurovascular bundle preservation.

Laser-assisted LNSRP remains experimental.

RENAL TUMOUR LASER INTERSTITIALABLATIONcurrent consensus for small renal tumours supports thermal coagulation as an alternative treatment option.

only in selected cases of patients with co-morbidities that make them unsuitable candidates for partial nephrectomy.There may be role but still experimental.Renal magnetic resonance imaging (MRI)-guided percutaneous laser thermal ablation (LTA) was first introduced by de Jode (1999).inoperable renal tumours Nd:YAG laser delivered percutaneously.water-cooled interstitial fibre. Using MRI, laser placement was guided and treatment monitored in real time. Tissue necrosis within the targeted tissue was confirmed.

Laser in Upper tract tccNd:YAGFor coagulation: 5-10 W for 2 sec.For ablation: 15 W for 2 sec.

Ho:YAGFor ablation: 0.6-1 J at 10 Hz.RETROGRADE LASER ENDOPYELOTOMY FOR PUJOoptimal indicationshort (< 2 cm) UPJO of intrinsic aetiology in the absence of, very large pelvis, high insertion of the ureter, renal split function below 20%, ipsilateral renal calculi.outcome of retrograde laser endopyelotomy compared to open pyeloplasty is slightly inferior.Retrograde laser endopyelotomy could be one of the first-line treatment options. Follow-up should be prolonged for at least 1 year post-operatively. Open or laparoscopic pyeloplasty remain options in cases in which minimally invasive measures fail.laser urethrotomy

Laser usedNd:YAG, KTP, Argon, Ho:YAG Diode laserNo superiority of one type of lasers has been demonstrated.Lack of large multicentre studies comparing the success rate of laser endourethrotomy with conventional OIU.A RCT comparing the effectiveness of Nd:YAG laser with conventional OIU in urethral strictures (0.3-2.4 cm): laser treatment significantly decreased the probability of therapeutic failure and recurrence of stricturesBladder neck contractureHo:YAG- 2 joules at 40 HzLASER IN PENILE CARCINOMAIndications of sparing surery:Primary tumors: stages Tis, Ta, T1 andgrade 1 and grade 2 tumors

CO2, argon, Nd:YAG, and KTP lasers.

M.C: Co2 laser-setting: 5-10 watts. The laser is applied until the tissue turns white, signifying adequate vaporization.