10-plus years of data show the GreenLight laser achieves outcomes equivalent to that of TURP.
For 30 years, lasers have been evolving for the treatment of urologic conditions. Investigators focused on lasers for BPH to achieve results similar to transurethral resection of the prostate (TURP) without the bleeding, fluid overload, blood loss, inpatient hospital stays of two to three days, and erectile dysfunction associated with TURP.
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For BPH, a laser must be able to vaporize tissue, coagulate the understructure, and have low absorption in water. It should be preferentially absorbed by the prostate. Of the lasers listed, the GreenLight KTP-532 is the ideal wavelength because it has a high affinity for oxyhemoglobin.
The wavelength of 532 nm is produced by focusing a neodymium YAG laser 1064-nm wavelength through a crystal that doubles the frequency, but halves the wavelength to 532 nm. The high absorption coefficient of blood for the GreenLight laser permits heat-induced coagulation, which creates a hemostatic surgical field. Precise tissue vaporization in a highly hemostatic environment promotes effective destruction and targets tissue ablation with minimal thermal coagulation.
Use of the KTP wavelength in high peak powers in excess of 280 watts with short pulse frequency allows high-density energy to be deposited in a shallow layer of tissue with an optical penetration depth of approximately 0.8 mm (Surg Clin North Am. 1992; 72:531-558; Urology. 1997;49:703-708).
This allows the targeted superficial tissue temperature to reach a vaporization threshold of greater than 100 C. A thermal gradient allows for heat diffusion to create a coagulation zone approximately 1-2 mm in diameter under the treated area (Appl Opt. 1983;22:676-681).
KTP lasers have been used for more than 20 years for urologic conditions such as urethral strictures, condyloma, and bladder carcinoma. The original KTP laser had low-power settings (16-38 watts), which limited vaporization for BPH. In the late 1990s, a high-powered 532 KTP GreenLight laser was developed (Laserscope/AMS, Minnetonka, Minn.) to implement the character-istics of the 532 KTP wavelength with increased power for rapid vaporization, using a solid state Q-switched KTP laser base.
Rapid, complete eradication
Endoscopic treatment of BPH by whatever surgical process should accomplish complete eradication of the entire adenoma causing outlet obstruction, and it should do so in a rapid manner that can be easily assessed at the conclusion of the operation. The method should also produce precise coagulation with limited blood loss and the ability to preserve erectile function and limit the potential for retrograde ejaculation (Contemporary Urology. 2005;17: 30-37).
The 532 GreenLight laser is the medical laser with the characteristic that best meets these criteria. The development of a high-powered KTP laser, capable of generating 60 watts, permitted creation of a large prostatic cavity (3 cm) in canine prostates (Urology. 1996;48:575-583). These studies led to clinical applications of 60-watt KTP laser vaporization prostatectomies, known as photoselective vaporization of the prostate (PVP). In 1998, researchers reported the first clinical series of PVP utilizing the KTP laser at 60 watts (Urology. 1998;51:254-256).
The study revealed no significant bleeding or fluid absorption. Foley catheters were removed within 24 hours in all patients. Mean improved flow rates of 143% were accomplished with minimal dysuria, hematuria, and no incontinence.
A study published in 1999 demonstrated a mean 124% improvement in peak urinary flow rate, and a mean 46% decrease in international prostate symptom scores (IPPS) at six weeks following laser therapy (BJU Int. 1999;83:857-858). Malek et al in 2000 reported on 55 men, demonstrating 82% improvement in the American Urologic Association (AUA) Symptom Score and a 278% increase in peak urinary flow rate at two years (J Urol. 2000;163:1730-1733).
Power increases to 80 watts
Laserscope accomplished an increased power to 80 watts in their subsequent laser. A multicenter clinical evaluation was established with patient evaluations pre- and post-study for symptom scores, urodynamics, and ultrasound imaging of the prostate.
In 98 patients, the study showed significant improvement in AUA Symptom scores, quality of life scores, peak flow rates, and postvoid residual volumes. None of the patients required transfusion, and there were no instances of erectile dysfunction (J Urol. 2003;169;suppl:465).
Malek and Kuntzman in 2003 reported their five-year experience with high powered KTP laser. This study showed durability in improved flow rates, symptom scores, and quality of life scores (J Urol. 2003;169:suppl:390. Abstract 1457). Malloy et al reported on a two-year follow-up of the multicenter study in 139 men (J Urol. 2004;171 [4 Suppl]:399 Abstract 1517). Patients were consistently treated in outpatient or 23-hour stay units. Results were comparable to TURP but with shorter hospital stays, minimal blood loss, less strictures, and no erectile dysfunctions. Most patients could return to work in 3-5 days and exercise within 14-20 days.
In 2006, investigators reported three-year results using the 80-watt power GreenLight Laser. Long range durability again was observed, and the PVP was also reported to be efficacious in patients on anticoagulants such as heparin, warfarin, or Plavix who could not have their drug ther-apy discontinued. Average operative time was 38.7 minutes, with an average prostate volume of 54.6 grams (BJU Int. 2006;97:1229-1233).
The 120-watt laser
In 2006, Laserscope-AMS introduced a new, higher power KTP Laser called GreenLight HPS, with power that could go as high as 120 watts. The unit was air cooled and could be used in any operating room. The 120 watts of quasi-continuous power allowed for higher vaporization efficiency and decreased operative time.
The laser featured a dual power mode with two foot pedals that allowed for vaporization or coagulation without the need to adjust power settings. An improved fiber with a reflective coating limited the back-scattering effect, which reduces the risk of lasing non-targeted tissue. The 120-watt power and beam characteristics required careful surgical technique so as not to injure the trigone, ureters, bladder neck, or membranous urethra.
The 80-watt GreenLight has a maximum focus and power density at 0.5 mm from the fiber to the tissue. This requires near-contact to the prostate for maximum vaporization. The GreenLight HPS, on the other hand, has a fiber with a beam that maintains focus with little divergence up to 3 mm from the fiber, and with limited divergence at 5 mm. The power density is maintained. Effective vaporization is obtained with increased distance from the target adenoma, allowing consistent vaporization even with variable distances from the fiber to the prostate.
The 120-watt power is a 50% improvement over GreenLight PVP, resulting in increased vaporization efficiency. For this reason, surgeon training is imperative because this laser is more dangerous if not operated with strict adherence to technique and consideration of anatomical landmarks. The ideal operation of GreenLight HPS should use a non-contact technique where possible. This limits damage and overheating of the fiber with maintaining maximum vaporization efficiency. The laser should never be operated unless the surgeon can see the GreenLight beam and it is focused on prostatic adenoma and not on the bladder.
At 120 watts, severe damage with perforation of the bladder or injury to the ureteral orifices will result if HPS power is inaccurately applied. The laser beam should be applied with a continuous sweeping technique producing bubbles from the vaporized prostatic tissue. If the beam remains on one area for a protracted period, deep coagulation occurs with potential for subsequent sloughing of tissue in the postoperative period. Proper continuous irrigation with saline is required to obtain clear surgical view of the operative area.
The laser power can be varied from 60 to 120 watts depending on the location and characteristics of the tissue being vaporized. Lower power settings should be used initially to test the efficiency of vaporization. In larger glands (greater than 100 grams), more power is used once the non-contact 3-to-5 mm distance from fiber to tissue can be obtained. The fiber should be cleaned periodically, to remove adherent tissue or carbonization, to preserve fiber efficiency.
The dual-power foot pedal allows instant application of lower 20- to 30-watt power, which is ideal for coagulation. This can be obtained without decreasing the power utilized for vaporization, which was necessary in the GreenLight PVP machine.
The GreenLight HPS allows the surgeon the flexibility to deliver efficient vaporization with minimum adverse effects and complete vaporization. Smaller glands (less than 35 grams) should be treated with 80 watts of power. Prostates up to 80 grams can be treated ideally with 80 to 100 watts. For adenomas greater than 80 to 200 grams, initial use of 80 watts and then increasing to 120 watts is recommended for the maximum efficiency. Prostates with large intravesical middle lobes should be vaporized with 80 watts to limit the possibility of inadvertent damage to the trigone, or bladder.
