Comparison of Intraoperatively Built Custom Linked (IBCL) Seeds to Free Seeds for LDR Prostate Brachytherapy

Abstract

Our prostate brachytherapy technique evolved from implanting free seeds using a gun applicator (GA) to using intraoperatively built custom linked (IBCL) seeds constructed with a push-button delivery system. In this work we compare our dosimetric and early clinical outcomes using free vs. IBCL seeds. From April 2005 to June 2012, 197 patients with clinically localized prostate cancer underwent brachytherapy using ultrasound-guidance with real-time intraoperative dosimetry based on the approach of Stock et al at Mount Sinai School of Medicine in New York. From April 2005 through February 2007, free seeds were placed using a GA. Starting in March 2007, brachytherapy was performed with IBCL constructed in the OR as needed during the implant. Length of each link, number of seeds in each link, and position of seeds and spacers in each link were based on optimizing real-time dosimetry. All patients underwent post-operative CT-based dosimetric analysis. Median follow-up was 3.1 years for all patients, 6.4 years for patients with free seeds, and 2.7 years for IBCL patients. Median age at diagnosis was 64 years and 66% were white. Median PSA at diagnosis was 5.97 ng/ml. NCCN risk grouping: low – 54%, intermediate – 39%, and high – 7%. 117 patients received I125 alone and 79 patients received Pd103 plus external beam radiation therapy (EBRT). One patient received Pd103 alone. Median prostate D90 was 172.1 Gy for I125 and 109.3 Gy for Pd103. Median prostate V100, urethra D30, and rectal V100 were 93.6%, 132.3%, and 0.55 cc. IBCL had significantly higher prostate V100 (p = 0.008) and D90 with I-125 (p = 0.008) than for free seeds while the urethra D30 and rectal V100 were not significantly increased (p = 0.443 and p = 0.651, respectively). 5-yr bDFS was 90.6% for intermediate/high-risk patients and 96% for low risk patients. 5-yr bDFS was significantly higher in the low risk group with IBCL at 100% compared to free seeds at 90.2% (p = 0.031). The 5-yr estimates of toxicity ≥ grade 3, urinary retention requiring catheterization, any hematuria, and any rectal bleeding were 3.4%, 4.7%, 10.2%, and 10.4%, respectively, with no significant difference between IBCL and free seeds. The 5-yr rate of rectal bleeding with radiation (RT) changes on colonoscopy was 1.8%. All hematuria resolved on its own with no RT changes on cystoscopy. Prostate implants using free seeds or IBCL seeds provide low rates of early biochemical failure and toxicity in patients with clinically localized prostate cancer. IBCL was associated with higher prostate doses in patients receiving I125without increasing normal tissue doses significantly. Patients with low risk disease had better bDFS with IBCL seeds compared to patients treated with free seeds, but longer follow-up is needed to confirm these findings.