The retrospective analysis of the relationship between prescribed dose and risk factor for seed migration in iodine-125 prostate brachytherapy

The aim was to determine the dose-specific incidence and predictors of seed loss/migration after permanent seed implantation (PI) for localized prostate cancer. The records of 79 patients with T1c-T3a prostate cancer who underwent prostate brachytherapy with loose iodine-125 seeds were retrospectively reviewed. Of these patients, 33 with low or intermediate risk underwent PI with the prescribed dose of 160 Gy for the clinical target volume (CTV), and 46 with high risk underwent PI with 110 Gy for the CTV followed by external beam radiotherapy (EBRT) with 45 Gy. Each CTV was defined as a contoured prostate. After PI, the incidence of seed loss/migration was assessed by a series of radiographs. Seed migration occurred in 22 (0.479 %) of 4589 implanted seeds 1 month after implantation. In PI alone, the number of needles (P = 0.081) and the number of seeds (P = 0.071) showed a trend for a difference between those with and without seed loss. In PI + EBRT, there was a significant difference in the discrepancy between the seed numbers calculated by the nomogram and actually implanted (P = 0.032). It is suggested that the discrepancy in seed numbers might be the predictor for seed migration in PI with 110 Gy.