lasers in urology

Lasers in Urology

Dr. Ahmad KharroubyPGY2, Surgery

Laser

Laser is an acronym that stands for light amplification by the stimulated emission of radiation

Laser physics

Einstein used 2 principles of physics as the basis for his discovery: (1) light travels in packets of energy

known as photons (2) most atoms or molecules exist

naturally in a ground or low energy state (E0)

Laser physics

By adding electricity, heat, or light energy to atoms in their ground state, their energy level can be raised

The energy then is released spontaneously in the form of photons or electromagnetic (EM) waves to return to the ground state

The concept of laser

When a photon of light energy of a certain wavelength strikes an excited atom (En), that photon and the photon(s) of light that is released are discharged simultaneously and therefore will be identical in frequency and phase

Anatomy of a laser The populations of atoms or molecules that

become excited are the lasing medium The lasing medium exists between 2 mirrors

for light amplification to occur; one is fully reflective and the other only partially reflective

Once the lasing medium at the core is excited by a pumping mechanism that supplies energy, a population inversion occur

Some photons are emitted spontaneously from the excited atoms or molecules that cause light to travel in all directions within the laser cavity

Difference between LASER & natural light

Coherence (the photons are all in phase)

Collimation (they travel parallel with no divergence)

Monochromaticity (they all have the same wavelength and, therefore, the same color if within the visible light spectrum)

Lasing medium

Different lasing mediums (which can be either solid, liquid, or gas) emit photons in different wavelengths of the EM spectrum

Factors affecting Laser

Other characteristics that affect laser performance are the power output and the mode of emission: Continuous wave Pulsed (more precise control and less

lateral heat conduction to tissues )

The physical properties of a laser

Can be described using 4 key concepts Energy describes the amount of work

accomplished and is measured in joules Power refers to the rate of energy expenditure

and is measured in joules per second, or watts (1 J/s = 1 W\

The fluence, describes the amount of energy delivered per unit area (J/cm2)

Irradiance is a term used to describe the intensity of a laser beam, and it is measured in watts per square centimeter

Pathophysiology

The biophysics of laser-tissue interactions

Factors affecting laser-tissue interactions: Local tissue properties Local blood circulation Laser:

wavelength Energy mode


Molecules, proteins, and pigments may absorb light only in a specific range of wavelengths

The biophysics of laser-tissue interactions The wavelength of laser light can

be proportional to the depth of penetration into specific tissues

The longer the wavelength, the deeper the expected penetration


Surgeons currently using lasers seek 4 different effects— Thermal Mechanical Photochemical tissue welding effects

The biophysics of laser-tissue interactions The most common utilization is the

thermal effect, whereby light energy is absorbed and transformed into heat


The mechanical effect results, for example, when a very high power density is directed at a urinary calculus

This creates a plasma bubble that swiftly expands and acts like a sonic boom to disrupt the stone along stress lines

The biophysics of laser-tissue interactions The photochemical effect refers to the

selective activation of a specific drug or molecule, which may be administered systemically but is taken up in selected tissues

The biophysics of laser-tissue interactions Finally, the tissue-welding effect is

derived by focusing light of a particular wavelength to induce collagen cross-linking

Laser types and clinical applications

Ruby laser The laser produces red light at a

wavelength of 694 nm The ruby laser is less efficient than

more modern lasing materials Used in a for removal of pigmented

lesions and tattoos, with little scarring

CO2 laser The CO2 laser emits in the invisible far

infrared portion of the EM spectrum, at 10,600 nm

It usually is coupled with a visible helium-neon beam for guidance

Its beam is highly absorbed by water Therefore, it vaporizes water-dense

tissues to a superficial depth of less than 1 mm

Neodymium:yttrium-aluminum-garnet laser ND:YAG is used commonly today because

of its efficiency The Nd:YAG laser emits a beam at 1064

nm (near infrared) Deep penetration of as much as 10 mm

because this frequency is outside the absorption peaks of both hemoglobin and water

It has good hemostatic (coagulates blood vessels as much as 5 mm in diameter) and cutting properties and also is suitable for lithotripsy

Potassium-titanyl phosphate crystal laser

(KTP) laser, yields a green visible light beam of 532

It is used for incisions, resection, and ablation

Alexandrite laser

This is a tunable laser The wavelength range is from 380-830 nm This light is absorbed well by melanin;

therefore, it can be used for cutaneous lesions

It is used for lithotripsy of pigmented stone This laser also can be used for tissue welding

Semiconductor diode laser Smaller, more efficient, and

potentially cheaper than most other lasers now in use

Their wavelength can be tuned These lasers currently are used for

tissue coagulation and thermal treatment of solid organs, including the prostate

Holmium:YAG laser Holmium:YAG (Ho:YAG) is a somewhat recent edition It consists of the rare earth element holmium, doped in a YAG

crystal that emits a beam of 2150 nm This laser energy is delivered most commonly in a pulsatile

manner It superheats water, which heavily absorbs light energy at this

wavelength This creates a vaporization bubble at the probe This vapor bubble expands rapidly and destabilizes the

molecules it contacts It is ideal for lithotripsy of all stone types The absorption depth in tissue is 1-2 mm, as long as it is used

in a water-based medium This specific light energy provides good hemostasis when

used in a pulsed mode of 250 ms duration and at low pulse repetition rate

It also may be used for incisions at higher repetition rates

Nitrogen laser It emits light with a wavelength of

337 nm Used as a diagnostic test for

transitional cell carcinoma (TCC) and other mucosal malignancies i.e. autofluorescence

Current laser applications

Urolithiasis Lasers are ideally suited for either retrograde

ureteroscopy or percutaneous nephrostolithotomy

Laser lithotripsy first was used clinically in the late 1980s, using the coumarin-based pulsed dye laser

The mechanism of action occurs via plasma formation between the fiber tip and the calculus, which develops an acoustic shock wave that disrupts the stone along fracture lines

Urolithiasis

The Ho:YAG is the best nowadays Allow for segmental resection of all

stones, regardless of their composition

Accurate fiber contact against a calculus is the primary safety factor

Laser therapy for benign prostatic hyperplasia

Laser prostatectomy The 2 main tissue effects are

coagulation vaporization

Laser therapy for benign prostatic hyperplasia Coagulation occurs when somewhat

diffusely focused laser energy heats tissue to 100°C

Proteins denature, and necrosis ensues This results in subsequent sloughing of

necrotic tissue This process often initially results in

edema, which increases prostate volume transiently (may require short-term Foley)


Vaporization occurs when greater laser energy is focused (increased power density) and tissue temperatures reach as high as 300°C

This causes tissue water to vaporize and results in an instantaneous debulking of prostatic tissue

Laser therapy for benign prostatic hyperplasia The high-power (80 W) potassium-titanyl

phosphate laser (KTP, or Greenlight) is commonly used for its vaporization effects

This procedure is associated with significantly less bleeding and fluid absorption than standard TURP

The KTP procedure is a safe and effective treatment option in seriously ill patients or those receiving oral anticoagulants

Drawbacks to the KTP procedure include the lack of tissue obtained for postoperative pathological analysis and the inability to diagnose and unroof concomitant prostatic abscesses

Laser therapy for benign prostatic hyperplasia Nd:YAG is used most commonly for its

coagulative effect The procedure is termed visual laser

ablation of the prostate (VLAP) Typically, segmental coagulation is

achieved by aiming for the 12, 3, 6, and 9 o'clock positions

The postoperative course may be complicated by irritative voiding symptoms because of the disrupted urethral epithelium

Laser therapy for benign prostatic hyperplasia The Ho:YAG laser have been used to incise

or enucleate prostate adenomas down to the capsule

The Ho:YAG is ideally suited for this task because it creates precise incisions, cuts by vaporizing tissue with adequate hemostasis, and leaves minimal collateral damage

Advantages of this method include the availability of a specimen for histologic examination, less postoperative catheter time, and the ability to excise large adenomas


Laser modalities are safer than TURP in the perioperative period (less bleeding & shorter hospital stay), although some may have a similar long-term complication profile

Laser treatment of urothelial malignancies

Most commonly, holmium and Nd:YAG are used in this setting The Nd:YAG laser energy is used to

coagulate and ablate with a thermal effect

Holmium is more precise, with less of a coagulative effect

Laser treatment of urothelial malignancies

Advantages less bleeding; consequently, catheter drainage

usually is not needed a lower incidence of stricture formation decreased need for anesthesia,& less postoperative

pain can be used in an office setting

Disadvantages no pathology specimen is available, obtain multiple

prior biopsy samples the area of destruction is deep and not fully visualized Some reports of bowel perforation exist

Laser treatment of urothelial malignancies Photodynamic therapy is another form of

tumor ablation where a systemically administered compound is absorbed or retained preferentially by cancer cells and converted by laser light to a toxic compound

This compound usually acts through oxygen radicals to destroy malignant cells

Lasers are suited ideally for this form of therapy

This is especially promising for TCC–carcinoma in situ (CIS), which shows complete responses

Lasers for urothelial stricture disease

Nd:YAG, KTP, and Ho:YAG lasers all have been used experimentally to vaporize fibrous strictures

They can have rates of recurrence similar to the cold-knife internal urethrotomy

Ureteropelvic junction obstructions, posterior urethral valves, and even bladder neck contractures recently have been treated using laser energy

Ho:YAG is most likely the best form of laser energy for these tasks

Ureteroscopic laser endopyelotomy is a minimally invasive, short-stay outpatient procedure associated with 73.1% success rate

Lasers for the ablation of skin lesions Lasers offer minimal scarring and superior

cosmetic results when compared with other forms of cutaneous lesion resection

Condyloma acuminata Penile carcinoma in the early stages (eg, CIS, T1 or

T2) Cutaneous hemangiomas (highly indicated)

FUTURE AND CONTROVERSIES

Laser energy is applied in a constructive manner to reapproximate tissues

The results are very promising thus far, with good tensile strength, watertight seals, and minimal scar formation

Tissue solders (albumin solutions) and chromophores added to tissue edges before reapproximation speed the welding process, increase tensile strength, and minimize collateral injury

This technology may be particularly helpful in laparoscopic surgery

Uses Vasovasotomy for vasectomy Hypospadias repair Pyeloplasty augmentation cystoplasty continent urinary diversion. Proposed future laparoscopic ureteroureterostomy laparoscopic Pyeloplasty laparoscopic Ureteroneocystostomy laparoscopic bladder and bowel anastomoses

Because urine lacks the clotting ability of blood, tight anastomoses of urothelial structures are even more important than in vascular surgery

Autofluorescence Light of 337 nm emitted by a nitrogen

laser and applied to bladder tissue can Identify Malignant tissue

This method of detection has yielded a very high sensitivity, specificity, and positive and negative predictive values, (97, 98, 93, and 99% respectively)

References

Prepared from emedicine website

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