Implanting radioactive seeds in the prostate to treat early stages of cancer may be as effective over the long run as surgery and more effective than external beam radiation, a new study suggests.

However, some questioned the conclusion of the study.With brachytherapy, tiny seeds of radioactive material are injected into the prostate to shrink the cancer from within. Patients treated with this method run a lower risk of urinary incontinence or impotence than with surgery, one of the most common ways to treat prostate cancer.

Until now, however, there had been no evidence of the long-term value of brachytherapy.

Without a comparison group, such studies are unlikely to prove beyond doubt that a particular treatment is better or worse than others. In this case, doctors did not directly compare brachytherapy with surgery in men who were the same age and had the same stage of disease.

The study conducted at Northwest Hospital in Seattle looked at 152 men 10 years after they were treated with radioactive seeds and, in some cases, beams of radiation from outside the body.

Five patients couldn't be located 10 years later. Of the 147 others, 97 - or 64 percent of the original number - remained free of disease and had low levels of prostate-specific antigen, which can be an early signal of the cancer. Only three patients died of prostate can-cer.

"It shows that brachytherapy is a proven, viable option for treating clinically localized prostate cancer," said Dr. Haakon Ragde, lead author of the study. "This is just as effective as the best surgical results and is more effect than conventional radiation beam results."