A considerable percentage of men who are treated with brachytherapy, also known as internal radiation therapy or seed implantation, for prostate cancer will have at least one pellet that ends up in the lungs, according to recent reports. The significance of this finding, however, is unclear at this time.

Brachytherapy, introduced in the US in the mid 1980s, has given men with cancer contained to the prostate gland an alternative treatment option to radical prostatectomy (surgical removal of the prostate) or external radiation therapy.

Brachytherapy involves the implantation of small radioactive pellets, or "seeds," into the prostate gland. These seeds give off radiation that travels only a few millimeters and kill nearby cancer cells. Because the seeds lose their radioactivity over the course of about two months, they are not removed after being placed.

Many men choose brachytherapy over other treatment methods because it can be done as a one-time, outpatient procedure with few short-term effects.

As a relatively new treatment, brachytherapy's long-term effectiveness is not well known. The level of long-term side effects (such as impotence and urinary incontinence) commonly seen in prostate cancer treatment is yet to be determined. Seed migration and possible side effects, however, is unique to brachytherapy.

Two separate groups have reported this year that pellets have shown up on chest X-rays in the lungs of men who have undergone brachytherapy.

Researchers from Robert Wood Johnson Medical Center in New Brunswick, N.J., found that radiation seeds could be seen in about 36% of patients. They reported their findings at a recent meeting of the American Urological Association and in The Lancet Oncology (Vol. 2, No. 8: 466).

Earlier this year, researchers from the University of Virginia Health Sciences Center in Charlottesville, Va., published a similar report in the Journal of Urology (Vol 165, No. 5: 1590-1596). According to their study, 29% of patients had seeds that had relocated to the lungs.

While seed migration has been reported in the past, the rate at which it occurred was always thought to be closer to 10%.

It is not known if seed migration is more likely immediately after placement (when the radioactivity is highest) or some time later. According to Murali Ankem, MD, at the Robert Wood Johnson Medical Center, none of the patients reported any symptoms that were likely to be associated with the seeds.

The number of seeds placed during a brachytherapy procedure depends on the size of the prostate gland, but the number can be in the hundreds. In most of the reported cases only one migrated seed was found.

Ankem says less that 1% of seeds are thought to move, and migration of a few seeds would have no impact on the effectiveness of the procedure. Possible long-term effects of the seeds on the lungs, however, are not known.

Researchers say that urologists and radiologists need to be aware of this problem so that patients can be monitored closely in the future. And, physician awareness will ensure that they don’t mistake the seeds in the lungs for foreign bodies on any subsequent X-rays a patient may have.