A technique that involves injecting radioactive seeds into the prostate to kill cancer may deliver an inadequate radiation dose to the prostate more than half the time, according to a doctor who trains physicians in the procedure.

"Based on what's been published over the last ten years, I'd say as many as 50 percent of patients in the U.S. get an adequate implant," says Nelson Stone, M.D., a urologist and clinical professor of urology, radiation oncology and oncological sciences at Mount Sinai Medical Center in New York City.

Dr. Stone, who is also medical director of Prologics, a company that operates and services radiation treatment centers in the United States, believes a careful review of the medical literature suggests that this life-saving procedure isn't working as well as it should.

In brachytherapy (from the Greek word brachy, meaning "short distance") doctors typically use an ultrasound to guide the placement of tiny radioactive seeds into the prostate. Once there, radiation emitted from the implants can eliminate cancers growing in the organ.

While highly effective if used properly, errors can be disastrous. Seeds intended for the prostate that miss might end up in the bladder, urethra or rectum. There, the seeds could cause serious radiation-induced injury. According to Dr. Stone, botched procedures can result in anal bleeding, fistulas and urinary incontinence.

Worse than the direct side effects, though, is that radioactive seeds lodged outside the prostate can't fully expose the cancers to radiation, which can lead to cancer recurrence, according to Dr. Stone.

What dosimetry studies reveal

After looking over the relevant literature for an upcoming article, Dr. Stone concludes these serious medical errors are startlingly common.

As Dr. Stone explains, the success of a procedure is generally determined by a post-implant dosimetry study to measure how much of the radiation dose was delivered to the prostate, and how much to outlying areas. In this, the key metric is the D-90, or the radiation dose to 90 percent of the prostate.

"That number, the dose to 90 percent of the prostate, has been highly correlated with the cure rate, in terms of eradicating prostate cancer," Dr. Stone says.

Typically, a minimum D-90 for the most common isotope used (I-125) should be 140 Gy. This dose is held as the benchmark to achieve for controlling cancer, according to Dr. Stone. But in his research he has discovered that as many as 50 percent of the brachytherapy procedures performed in the United States fail to reach 140 Gy. This means that one half the patients may be getting too low a dose.

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