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.