Iodine 125 versus palladium 103 implants for prostate cancer: clinical outcomes and complications

The purpose of this study was to evaluate the clinical outcomes and compare complication rates for patients with prostate cancer treated with iodine 125 ((125)I) and palladium 103 ((103)Pd) prostate brachytherapy at a single institution.

Between 1992 and 2002, 272 patients with prostate cancer were treated with ultrasound-guided transperineal implantation incorporating (125)I (107 patients) or (103)Pd (165 patients). Three months of hormonal therapy was incorporated into the treatment program in 33% of the patients in both groups. Nineteen percent of those treated with (125)I were treated with a combination of implantation plus external-beam radiation therapy. Only 6% of the group receiving (103)Pd implants were treated with such a combination. For those treated with (125)I implantation alone, the minimum tumor dose was 145 Gy. The minimum tumor dose for those treated with (103)Pd alone was 125 Gy. Those treated with a combination of external-beam radiation therapy and (125)I received 45 Gy via 1.8-Gy fractions followed by implantation with a minimum tumor dose of 110 Gy. For those treated with external-beam radiation therapy and (103)Pd, the doses were 45 Gy via 1.8-Gy fractions followed by implantation with minimum tumor dose of 98 Gy. Outcomes were evaluated based on radionuclide used, T stage, Gleason score, prostate-specific antigen, and prognostic group. Complications were also evaluated for each radionuclide. The mean follow-up for the (125)I group was 55 months, and the range was 12-108 months. The mean follow-up for the (103)Pd group was 44 months, and the range was 12-72 months.

The 5-year biochemical disease-free survival rates for those in the favorable group (clinical stage T1c or T2, prostate-specific antigen level <10, Gleason score <7) were 92% for the (125)I group and 92% for the patients treated with (103)Pd. The 5-year disease-free survival rates for those in the intermediate and poor prognostic groups, which were combined, was 72% and 74%, respectively, for (125)I and (103)Pd. There was no statistically significant difference for either modality for any treatment group tested. In those treated with implantation alone, patients treated with (125)I had higher complication rates than those treated with (103)Pd (15% vs 4%). (125)I-treated patients had a grade 2 complication rate of 8% and a grade 3-4 complication rate of 7%, compared with 3% and 1%, respectively, for the (103)Pd-treated patients.

Despite the different management recommendations that evolved during the study period, the clinical outcome for patients treated with either radionuclide were similar with respect to biochemical disease-free survival. Although specific dosimetric comparisons are not valid given differences in imaging over the study course, the complication rate appears to be somewhat higher for (125)I, which is consistent with a radiobiologic model.