Purpose: The present study was undertaken to determine the incidence and predictors of seed migration after transperineal interstitial prostate brachytherapy using I-125 free seeds. Methods and Materials: Between September 2004 and November 2007, 158 patients who underwent transperineal interstitial prostate brachytherapy as monotherapy for clinical T1/T2 carcinoma of the prostate gland were reviewed. Implants had been performed with standard techniques. All 158 patients underwent followup radiographs (orthogonal chest radiographs, a kidney-ureter-bladder radiograph, and a posteroanterior pelvic radiograph) to assess the presence of seed migration at 3 months after transperineal interstitial prostate brachytherapy. Patient characteristics and treatment status were recorded. Univariate and multivariate analyses were performed to identify predictors of seed migration. Results: Seed migration occurred in 35 of 158 patients (22.2%). Univariate analyses revealed that preoperative prostate volume estimated by transrectal ultrasound, the number of needles, the number of seeds implanted, and the presence or absence of pubic arch interference (PAI) were significantly associated with seed migration. These results indicated that larger prostate glands were more likely to have seed migration. However, the absolute difference in prostate size was not overly impressive (22.4 vs. 26.3 cm3). Multivariate analysis revealed that the number of seeds implanted and the presence or absence of PAI were significant predictors of seed migration. Conclusion: The number of seeds implanted and the presence or absence of PAI provide the most predictive information on seed migration.
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