Long-term outcomes of a prospective randomized trial of 131Cs/125I permanent prostate brachytherapy

Iodine-125 (125I) is the most commonly used isotope for prostate brachytherapy (BT). Cesium-131 (131Cs) has a higher dose rate and shorter dose delivery time resulting in decreased duration of acute urinary morbidity. Long-term data suggest excellent oncologic outcomes; it is not known how outcomes compare. A prospective randomized trial comparing the two isotopes was initiated. Patients with low- or intermediate-risk disease were treated with a BT in a single outpatient facility. Prescription dose was 144 Gy for 125I and 115 Gy for 131Cs. Androgen deprivation or supplemental EBRT was not allowed. The primary study objective was comparison of the mean EPIC Urinary Domain Score. Secondary objective was biochemical relapse-free survival (BRFS) comparison. Time-to-event for all outcomes of interest was measured from implant date. One hundred forty men were enrolled; 81.4% were low-risk and 18.6% were intermediate-risk. The median followup was 97 months. Urinary and sexual health-related quality of life did not differ between isotopes at any recorded time point. At 2 months after implantation, bowel health-related quality of life was worse with 125I; however, this difference was lost at subsequent time points. The 9-year BRFS was 87.2% and 84.0% for the 125I and 131Cs group, respectively (p = 0.897). There was no statistically significant difference in BRFS based on initial T stage, PSA, or Gleason score. Short- and long-term urinary, sexual, and bowel quality of life, as well as long-term biochemical control were comparable between 125I and 131Cs. This report therefore supports the continued use of 131Cs as an effective and comparable alternative isotope.