Brachytherapy Seeds May Migrate to the Patient’s Lungs

NEW ORLEANS—After brachytherapy for prostate cancer, a small proportion of the radioactive seeds migrate into the lungs of more than a third of patients, according to a report from the American College of Surgeons 87th Clinical Congress.

Researchers from the Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, said this occurrence has not proved harmful, but they recommend that clinicians inform their patients of the possibility of seed migration and order a follow-up chest x-ray.

Robert E. Weiss, MD, associate professor of urology, said that pulmonary migration has been reported in the radiology literature but is not commonly appreciated by urologists. Furthermore, the incidence of pulmonary seed migration may be greater than previously reported, he said.

While the incidence has been thought to be between 6% and 29%, the current study documented seed migration in 21 of 58 patients (36%). The tiny seeds (5 mm long and 0.5 mm in diameter) were found by chest radiography 2 weeks to 3 months after ultrasound-guided prostate brachytherapy.

While seed migration was common, only 34 (0.49%) of the 6,878 pellets actually migrated to the lung. Nine patients had single seed migration to the right lung, and three patients to the left lung. Nine patients had multiple and bilateral seed migration, with the most number of seeds per patient being four.

There seemed to be no consistent relationship between seed migration and the type of seeds used, but migration occurred more often in patients with the most seeds implanted. Repeated chest radiography in these 21 patients revealed no delayed migration, at a median follow-up of 16 months.

CT scans of the 21 patients showed that 14 (67%) had extracapsular seed implantation, and the investigators suspect this may have contributed to the higher incidence of seed migration in their study.

The study also evaluated the patients by clinical and pulmonary function testing and found no consistent abnormality attributable to seed migration.

"While these seeds migrate, there are no short-term effects on the lungs," Dr. Weiss emphasized. "The amount of radiation in the seeds is probably not enough to cause problems, but nobody has studied this long term. We think that urologists and their patients should be aware of this possibility."

Murali K. Ankem, MD, principal author and fifth year resident in urology, said that patients are often concerned that the brachytherapy will be compromised by seed migration. But he pointed out that enough seeds are implanted around the prostate that the migration of a few should not diminish efficacy.