Mahmood A. Hai M.D., F.A.C.S.,Westland,Michigan
Reprinted from PCRI Insights November 2005 vol. 8, no. 4
During the last two decades, lasers have penetrated into most of the fields of medicine and in many cases have revolutionized the way we diagnose and treat patients. Many specialties have integrated lasers into clinical practice for the use of incision, excision, resection and ablation of soft tissue. The field of urology has found many useful applications for various laser wavelengths. For many years, laser utilization has focused on areas of prostate disease that include benign prostatic hyperplasia (BPH) and prostate cancer (PC). The later has been studied and evaluated with little enthusiasm. One reason stems from the anatomical differences in the growth of prostate tissue. Benign neoplasm of the prostate grows in an area referred to as the transition zone of the prostate. Conversely, prostate cancer predominately grows in the central and peripheral zones of the prostate. The anatomical and tissue compositional differences create inherent restriction in the types of lasers available for treatment.
|Figure 1 Zones of the Prostate|
Application of Laser Technology to Date
A promising form of laser therapy has involved the use of high-power lasers to palliatively remove prostatic obstruction secondary to the prostate cancer. Among the lasers available, potassium-titanyl-phosphate (KTP) has received the most attention. The pilot study reported by Hai and Malek indicated that photoselective vaporization of the prostate (PVP) with 80 watt KTP was a simple, safe and efficacious outpatient procedure for the treatment of obstructive BPH.1 Due to its laser tissue interaction and optical absorption characteristics, the KTP laser can safely and effectively remove the prostatic adenoma with minimal postoperative morbidity.2 The treatment is often employed to relieve (1) urinary symptoms caused by the benign growth of the prostate and (2) those which may be caused by a prostate tumor before a primary cancer treatment is offered.
This treatment has proven successful in limited published clinical series. Kumar reported in a series of 10 patients with confirmed diagnosis of either or both BPH and prostate cancer that he could safely remove up to 50% of the prostatic obstruction, as measured by transrectal ultrasound, with the high-powered KTP laser.3 More importantly, there were no significant adverse events that accompanied the procedure. This includes stress urinary incontinence and excessive bleeding, which are events that can be derived from transurethral resection of the prostate (TURP). Moreover, the procedure may be offered as an outpatient modality. This facet of the procedure could prove to be a cost effective measure that possibly could enjoy cost savings for the health care system. However, this would need to be evaluated in a well-designed cost-benefit analysis.
Application to Prostate Cancer
At present, the existing data from which to draw definitive conclusions is limited, but the established clinical outcomes from cases where KTP lasers were used for treatment of benign prostatic obstruction cause us to be very hopeful. A significant number of urologists have adopted the PVP procedure for its clinical effectiveness in treating BPH. The rationale for extending the PVP applications to prostate cancer stems from the near bloodless de-bulking properties of the laser and for its precise and accurate vaporization capabilities. Using PVP for high-risk patients and for patients on active anticoagulation therapy could also broaden the demographic of patients that could be considered for treatment.4
The laser’s tissue interaction characteristics led most researchers to believe that high-power KTP, also known as the GreenLight PV® laser system (manufactured by Laserscope™, San Jose, CA www.laserscope.com), could provide a palliative treatment option for men with obstructive uropathy secondary to BPH and/or for prostate cancer. The 532nm wavelength is in the visible range of the electromagnetic spectrum. The high absorption curve at 532nm denotes a significant absorption to oxyhemoglobin (02Hb), and it is this high absorption coefficient that accounts for the near bloodless treatment effect on prostate tissue. The GreenLight absorbs and coagulates arterial
and venous bleeders with significant efficiency.
Another unique characteristic of the KTP laser wavelength is the shallow optical penetration depth. With only a 0.8 mm optical depth of penetration, there is a minimal thermal diffusion depth which limits the zone of coagulation to 1 – 2 mm in tissue.5 These two optical properties combine with high-power density to produce a tissue vaporization effect with minimal bleeding and limited thermal coagulative necrosis (scar tissue). Hence, the excitement for utilizing this tool as an adjunct treatment to obstructive symptoms caused by prostate cancer is spreading.
Researchers at the Cleveland Clinic Foundation and at Cornell University in New York have been using the GreenLight laser for palliative treatment of PC for well over two years. Preliminary clinical data presented at the 2003 North Central Section of the American Urological Association (AUA) showed that PVP could be used safely and effectively for patients as a post-radiation therapy and for patients with iodine (I125) seed implants. In addition, it has promise for post-treatment of brachytherapy, or the use of implanted seed radioactive isotopes. Brachytherapy patients often suffer from acute urinary retention as a result of thermally induced edema, which causes bladder outlet obstruction. If the obstructive adenoma is vaporized, the bladder outlet is relieved and patients are often voiding without intermittent catheterization. Moreover, the treatment is minimally invasive and normally does not require an overnight stay in the hospital.
Preoperative treatment with PVP may also prove to be a useful technique for reducing the volume of the prostate prior to radiotherapy. If the size of the prostate is reduced, a greater radiotherapy dose can be delivered to a smaller volume of tissue, thereby reducing the risks of complications. Only limited data is available in respect to combining the palliative effects of PVP with hormonal therapy for treating prostate cancer. PVP has also been successfully used in patients with prostate cancer who are obstructed and who have opted to have no other form treatment for their cancer.
My personal experience using PVP for treating obstructive prostate cancer has also demonstrated a high level of patient satisfaction. I have performed over 30 of these procedures, and all of my patients have experienced effective and sustained relief from their obstructive symptoms. As this treatment becomes more available, additional data and further clinical validation will ensue. But in the meantime, the clinical results have been very promising.
Prostate cancer patients with localized disease often suffer from the same symptoms as those with patients with BPH. Obstructive urinary symptoms such as weak urinary stream, hesitancy, terminal dribbling and urinary retention normally can be traced to an enlarged and obstructive prostate. By removing the anatomic obstruction, which contributes to lower urinary tract symptoms, patients are relieved of a debilitating and socially distressing quality of life. Urinary flow rates are significantly improved, post-void residual urine volumes are reduced and obstructive and irritative symptoms are improved.2 The PVP procedure can be used as an outpatient modality with very minimal side effects and expedient recovery. Treating PC patients with PVP as a palliative therapy either before or after treatment of the primary diagnosis should develop into an effective option for many prostate cancer patients who do not want to suffer from the agonizing and annoying symptoms of an obstructed prostate.
How the GreenLight PV™ Laser System Works
The latest innovations in laser technology have led to the development of the GreenLight PV™ laser system by Laserscope of San Jose, California) to help the relief of obstructive prostate for both benign and malignant tissue. The device uses a high-power, solid-state, Q-switched potassium-titanyl-phosphate (KTP) laser platform. The KTP laser employs a 1064-nm neodymium: yttrium-aluminum-garnet (Nd:YAG) laser beam passed through a KTP crystal to emit visible green light that is frequency-doubled to a wavelength of 532nm.
With its unique optical properties, the KTP laser wavelength can be utilized in an aqueous environment through a PV™ Laser System side-firing fiber optic device that delivers un-attenuated laser energy to the targeted tissue. High peak powers in excess of 280W (average power of 80W), and short pulse frequencies allow high-density energy to be deposited in a shallow layer of tissue; the optical penetration depth is approximately 0.8 mm. This allows the targeted superficial tissue temperatures to reach the vaporization threshold of >100°C. A shallow thermal gradient allows for limited heat diffusion to create a coagulation zone of approximately 1-2 mm. The high absorption coefficient of blood for green light permits heat-induced coagulation, which creates a hemostatic surgical field. Therefore, precise tissue vaporization in a highly hemostatic environment promotes effective and target-specific tissue ablation with minimal thermal coagulation.
The laser itself is a 220V, 50-amp system that is used primarily in the operating room of most hospitals although many well equipped offices and physician ambulatory surgery centers are equipped with the proper electrical and water capabilities to utilize the laser system. Also recommended for use in conjunction with the laser system are video towers used for urethral endoscopy, continuous flow cystoscopes, specially designed video camera filters, and goggles.
The procedure involves the use of general or spinal anesthesia and is considered a minimally invasive surgical intervention. The physician delivers a 22-23 Fr. continuous flow cystoscope directly into the urethral channel and into the prostatic fossa. A specially designed side-firing 70º angled fiber optic laser delivery device, known as the ADDSTAT®, is deployed through a laser fiber delivery port on the continuous flow cystoscope. The fiber is then used to deliver high-pulsed KTP laser energy directly onto the prostate or obstructive tissue in order to vaporize the obstructing tissue. The resultant effect creates an open prostatic fossa directly caused by the vaporizing effect of the laser. This in turn allows for debulking of the obstructing tissue and complete relief of the obstructing symptoms secondary to uropathy.
1. Hai MA, Malek RS. Photoselective Vaporization of the Prostate: Initial Experience with a New 80 W KTP Laser for the Treatment of Benign Prostatic Hyperplasia. Journal of Endourology, Volume 17, Number 2, 93-96,March 2003.
2. Te AE, Malloy TR, Stein BS, Ulchaker JC, Nseyo UO, Hai MA, Malek RS. Photoselective Vaporization of the Prostate for the treatment of Benign Prostatic Hyperplasia. 12-Month Results from the first United States Multicenter Prospective Trial. J Urol; Vol 172; 1404-1408, 2004.
3. Kumar SM. Photoselective vaporization of the prostate: a volume reduction analysis in patients with lower urinary tract symptoms secondary to benign prostatic hyperplasia and carcinoma of the prostate. J Urol; 173(2): 511-513, 2005.
4. Reich O, Bachmann A, Siebels M, Hofstetter A, Stief CG, Sulser ST. High power (80 W) potassium-titanyl-phosphate laser vaporization of the prostate in 66 high-risk patients. J Urol; Vol 173: 158-160, 2005.
5. Malek RS, Barrett DM, Kuntzman RS. High-power potassium-titanyl-phosphate (KTP/532) laser vaporization prostatectomy: 24 hours later. Urology; 1998 Feb; 51(2):254-6.