PURPOSE: To evaluate the feasibility,efficacy,and safety of permanent 125I seed interstitial brachytherapy reirradiation in patients with retroperitoneal lymph node recurrence under CT guidance.METHODS AND MATERIALS: Seventeen patients with 19 retroperitoneal lymph node recur-rence after external beam radiotherapy underwent CT-guided 125I seed implant brachytherapy from October 2007 to August 2014.Treatment for all patients was preplanned using a three-dimensional radiation therapy planning system 3-5 days before brachytherapy;dosimetry verification was per-formed immediately after brachytherapy.RESULTS: The actuarial D90 (dose delivered to 90% of the target volume) was 100--198 Gy (median,126.5 Gy).In 9 patients,pain intensity decreased to mild pain 1-3 weeks after brachy-therapy.Pain-free survival ranged 2-15 months (median,5 months;95% confidence interval[CI]: 0.1,9.9).The overall response rate was 19 of 19 (100%).The median local control time was 15 months (95% CI: 2.3,27.7).The 6-,12-,and 24-month local control rate was 88.0%,63.2%,and 42.1%,respectively.Twelve patients (70.6%) developed distant metastases and died.Two patients (11.8%) are alive with distant metastases but no evidence of local recurrence.Three patients (17.6%) are alive with no evidence of local recurrence.Median overall survival was 10 months (95% CI: 5.7,14.3);the 1-and 2-year survival rates were 38.1% and 15.3%,respectively.No major complications related to the procedure occurred during or after brachytherapy.CONCLUSIONS: Reirradiation with CT-guided permanent 125I seed interstitial brachytherapy is feasible,safe,and effective as pain relief or salvage treatment for patients with recurrent retroper-itoneal lymph nodes.(C) 2015 American Brachytherapy Society.Published by Elsevier Inc.All rights reserved.