Heat patterns, necrosis vary for BPH systems

March 1, 2005

Mumbai, India—More and more urologists are investing in heat-based treatment systems for BPH, and Thayne Larson, MD, a staff member with the Institute of Medical Research in Scottsdale, AZ, wants to make sure they're being smart shoppers.

Mumbai, India-More and more urologists are investing in heat-based treatment systems for BPH, and Thayne Larson, MD, a staff member with the Institute of Medical Research in Scottsdale, AZ, wants to make sure they're being smart shoppers.

Dr. Larson presented data on temperature patterns and tissue necrosis for two such heat-based devices-the Prolieve Transurethral Microwave Thermodilatation System (Boston Scientific/Celsion, Natick, MA) and the Tmx-2000 (American Medical Systems/TherMatrx, Minnetonka, MN)-at the World Congress on Endourology here.

His goal, he says, was simply to provide his colleagues with sound scientific information on which to base their purchasing decisions.

Prolieve, which earned FDA approval in early 2004, delivers 915 MHz of microwave energy while compressing the prostate with a 46F balloon inflated with circulating heated water. Balloon compression facilitates deeper penetration of the microwave energy while preserving an area of viable tissue around the urethra.

Dr. Larson and colleagues treated 10 BPH patients with Prolieve. In each one, they placed six closed-end, 17-gauge needles perineally under ultrasound control at various distances from the urethra.

Fiberoptic temperature probes, each with four sensors placed 1 cm apart, were then placed into each needle. That configuration allowed the investigators to measure interstitial temperatures at up to 24 locations every 10 seconds.

"The best way to describe [the Prolieve] is that it lies somewhere between the very high-energy machines that cause a great deal of necrosis and the low-energy machines without much necrosis," Dr. Larson said. "It's especially easy on the patients."

Indeed, patients treated with the Prolieve tend to report very little discomfort, and most can go without a Foley catheter afterward. The device's symptomatic relief is also comparable to its competitors, Dr. Larson said.

The Prolieve achieved thermotherapy temperatures (≥45 degrees Celsius) at distances of 2 to 14 mm from the urethra, with a peak near 7 mm and an exponential decay beyond. Temperatures above 45 degrees were recorded in all 10 prostates, while eight patients had temperatures above 50 degrees, Dr. Larson explained.

Gadolinium-enhanced MRIs performed 1 week post-treatment suggested zones of coagulative necrosis consistent with the temperature profile recorded by the probes. The average amount of necrosis was 6.5 cc.

"The Prolieve can produce sufficiently high temperatures within the prostate to cause necrosis, but it still preserves an average of 4.2 mm of tissue around the urethra, which may be the reason patients feel comfortable during treatment," Dr. Larson said.

Lower-energy unit The lower-energy Tmx-2000 was tested in five patients with lower urinary tract symptoms. The researchers employed the same system of interstitial temperature mapping and MRI analysis as was used in the Prolieve study.

The Tmx-2000 achieved its highest temperatures-about 50.5 degrees Celsius-only at the junction of the catheter and urethra. Temperatures fell off in a fairly consistent manner as the microwave energy entered the prostate, about 1.5 degrees/mm for the first 4 mm and about 1.0 degree/mm thereafter, with lower temperatures toward the base and apex.

"That's not hot enough to cause any real necrosis," said Dr. Larson. "Only the area 2 to 3 mm from the urethra is being treated with any significant temperatures greater than 45 degrees."

Post-treatment MRIs revealed minimal, patchy areas of necrosis, and those were seen only in the periurethral zone. The average amount of necrosis was 0.45 cc.

Boston Scientific funded the Prolieve study, while four different thermotherapy device manufacturers contributed to a non-restricted educational grant to support the Tmx-2000 study.