3-D mapping technique guides prostate cancer biopsies, treatment

May 15, 2008

A new 3-D technique for mapping biopsies and targeting focal therapy appears promising for imaging and guiding treatment of low-risk prostate cancers.

Scottsdale, AZ-A new 3-D technique for mapping biopsies and targeting focal therapy appears promising for imaging and guiding treatment of low-risk prostate cancers.

"If one does a biopsy in each of these 5-mm holes, one will, in fact, detect all the significant cancers," he said, citing a study in BJU International (2005 96:999-1004). "After the initial biopsies, we do biopsies that are tailored to the size of the prostate to determine if the patient is a candidate for targeted focal therapy. That may be anywhere from 40 biopsies to more than 100."

Although the procedure can be performed under local anesthesia, Dr. Crawford said general anesthesia is usually more effective. The procedure also requires a stepping unit similar to that used in brachytherapy.

Using a new 3-D imaging system developed with his colleagues, coupled with an ultrasound machine (B-K Medical Systems, Wilmington, MA), "we're able to get a real-time 3-D image of the prostate as we set up for the procedure," he said. The imaging system helps to guide the placement of stabilizing needles used as fiduciary markers.

"We will place several needles in the prostate that we will use initially so we can line the prostate up the same all the time. That's important if we're going to be targeting a specific area," he explained.

Once the prostate is stabilized, the physician inserts a needle through as many of the 5-mm holes as are needed and takes tissue samples. Dr. Crawford recommended placing each sample into individually marked jars specifying which row and column the sample came from. This will provide the necessary coordinates to treat the identified cancer.

"One thing to watch out for is that when a physician inserts these needles, there's going to be some deflection. They are not always going to go in straight," he added.

However, the stabilizing needles help combat this problem, as does introducing the needles slowly and meticulously with guidance from the 3-D real-time imaging system.

The procedure is fairly well tolerated, Dr. Crawford said. However, because retention is an issue with larger prostates, he recommends choosing patients carefully.

"One of the things we've learned is that it's probably unwise to do these biopsies on really large (80- to 100-gram) prostates," he said.

At that size, too many biopsies would be required to produce a complete clinical picture.

"With some of the 5-mm holes, a physician may have to use two or three passes with the needle to capture the whole length of it," he explained.

Because BPH, not prostate cancer, drives most of the initial biopsies, Dr. Crawford and his colleagues shrink large prostates for 3 to 6 months with a course of dutasteride (Avodart) before performing the procedure. The resulting shrinkage reduces the number of biopsies needed as well as the risk of post-biopsy complications.

The system also uses biopsy results to construct a 3-D model of a patient's cancer that physicians can use to guide them in performing targeted ablative procedures.