Seed migration in prostate brachytherapy depends on experience and technique.
PURPOSE
To determine seed loss and pulmonary migration rate over time in permanent seed prostate brachytherapy.


METHODS AND MATERIALS
We analyzed the first 495 patients treated in our department. All patients were treated with loose (125)I seeds with automated seed delivery system and real-time intraoperative planning. Pelvic fluoroscopic imaging was done 30 days after the implant. Patients were divided into five groups of 100 patients according to the order they were treated, and groups were compared using χ(2) test and one-way analysis of variance.


RESULTS
A total of 22.8% of patients lost at least one seed. The highest percentage of patients losing any number of seeds was in the first 100. Thirty-eight percent lost at least one seed. This number decreased gradually and was only 9% in Patients 400-499. The mean total seed loss rate (number of seeds lost/number seeds implanted) changed significantly over time (p<0.001). There was a continuous significant (p<0.001) decline after the first 100 patients (1.25% for the first 100 patients) followed by a rise in Patients 300-399, followed by another decline (0.21% for the last 100 patients). The seed loss rate to the thorax changed significantly over time (p=0.009). It rose after an initial rate of 0.25-0.42% in Patients 200-299 and 300-399 and declined later to a rate of 0.21% in the last 100 patients.


CONCLUSIONS
We found a learning curve for seed migration. Avoiding implanting seeds outside of the capsule and modern transrectal ultrasound imaging can help decrease migration.