Dosimetric analysis of urinary morbidity following prostate brachytherapy (¹²⁵I vs. ¹⁰³Pd) combined with external beam radiation therapy

The purpose of this analysis was to correlate isotope selection with the urinary symptoms of patients who received a combination of external beam radiotherapy (EBRT) and a transperineal interstitial permanent prostate brachytherapy (TIPPB) boost with either a ¹⁰³palladium (¹⁰³Pd) or a ¹²⁵iodine (¹²⁵I) radioisotope. Postimplant dosimetry was performed to evaluate both urethral dose and implant quality. The American Urologic Association (AUA) scores in both the ¹²⁵I and ¹⁰³Pd groups were similar initially. However, at 1, 3, 6, and 12 months of follow-up, the mean AUA scores for the ¹²⁵I and ¹⁰³Pd patients were 18 ± 6 vs. 11 ± 9, 17 ± 7 vs. 11 ± 7, 10 ± 3 vs. 9 ± 4, and 14 ± 8 vs. 7 ± 5, respectively (P < 0.01). The only significant difference between the postimplant dose-volume histogram (DVH) of the ¹²⁵I and ¹⁰³pd implants was the minimum dose that 90% of the urethra received (D₉₀). The increased AUA score of the ¹²⁵I group was weakly correlated (R² = 0.20) with the D₉₀ dose but that of the ¹⁰³Pd patients was not (R² = 0.00). This suggests that the higher AUA score of the ¹²⁵I patients was not necessarily the result of the higher D₉₀ dose. Thus, patients who received ¹⁰³Pd experienced less urinary morbidity than those implanted with ¹²⁵I. We recommend further validating these findings in prospective studies in which the quality of the ¹²⁵I and ¹⁰³Pd implants can be evaluated.