Swelling of the prostate gland by permanent brachytherapy may affect seed migration

The purpose was to monitor implanted seeds and to determine factors contributing to seed migration after permanent prostate brachytherapy.

Sixty-two consecutive patients with Stage 1 prostate cancer who underwent brachytherapy with (125)I seeds between February 2008 and May 2009 were studied prospectively. On post-operative days 1, 7 and 30, scintigraphy was added to conventional radiography to monitor the migration of the implanted seeds. The prostate volume was measured during the pre-planning stage using ultrasound and during the post-planning stage using computed tomography on post-operative days 0 and 30. Magnetic resonance imaging was performed on day 30.

Of the 4843 seeds implanted in the prostates of 62 patients, 108 seeds (2.2%) in 43 patients (69.4%) exhibited seed migration. Thirty-five seeds could not be identified using any of the imaging modalities and were likely passed during urination (0.7% of the total number of seeds). The maximum number of migrated seeds in one patient was 10 of the 85 implanted seeds. The fraction of patients with seed migration or loss increased from 27.4% on day 1 to 69.4% on day 30. The number of seeds that had migrated from the prostate increased from 48 (0.1% of the total number of seeds) on 1 day to 78 (1.0%) on day 7 and 108 (2.2%) on day 30. Of the seeds lost from the prostate, 38.9% embolized to the lungs. The seed loss during the first post-operative month was closely correlated with the swelling of the prostate gland between the pre-planning measurement and the post-planning measurement performed on day 0 (P < 0.0001).

Prostate swelling between the pre-planning and post-planning (day 0) measurements was significantly associated with seed migration, and adequate attention should be given to this issue.