Determinants of prostate volume changes following iodine-125 interstitial prostate implant

Abstract

15563 Purpose: Prostate brachytherapy (PB) has been linked with increase in prostate volume (PV). This study evaluates post- operative PV changes and the variables that might affect prostate swelling. Methods: Twenty four patients (pts) were analyzed. Twelve were treated with PB only, 8 with external beam radiation (EBRT) prior to implant, and 4 with EBRT after PB. Pre-treatment PSA and Gleason score ranges were 1.9–10.8 and 5–8 respectively. Pre- implant and post-implant day 1, 9, 30, and 60 (PV0, PV1, PV9, PV30, and PV60) measurements were done using computed tomography. Univariate analysis of PV change and the following was done: PV0, number of needles, seeds, and needle insertion attempts, seed activity (0.3 vs 0.5mCi), hormonal ablation therapy, and prior EBRT. Urinary symptoms were assessed using International Prostate Scoring System (IPSS). Results: Ninety six PV measurements were done by a single observer. PV0 ranged from 27.1 to 89.4 cc (mean 48.2). Largest PV was observed on day 1 (40.1–118.7, mean 67.1). Successive PV measurements afterwards continued to decrease. Mean PV values on day 9, 30, and 60 were 58.6, 51.5, and 42.3cc respectively. The differences between PV0 and all successive PV’s were statistically significant. Mean increase in PV1 from PV0 was 18.9±16.8cc (p<0.001), PV0 and PV9 9.7cc, PV0 and PV30 2.6cc. PV60 was smaller than PV0 by an average of 6.6cc. Statistically significant positive correlation was found between PV increase and seed activity (p=0.02) while treatment with EBRT prior to PB was associated with less prostate swelling (p=0.043). Other variables were not significantly correlated with PV changes. Although the mean IPSS score increased from pre-implant value of 9.2 to 13.7 on day 60, the differences between IPSS values were not statistically significant. Conclusions: Maximum prostate size is observed on the first day after implant. Prostate begins to decrease in size between day 1 and day 9 and reaches pre-procedure volume after day 30. Higher seed activity results in greater prostate swelling, while less brachytherapy- induced swelling is observed in patients treated with external radiation prior to implant. Resolution of prostate swelling does not appear to parallel with improvement in urinary symptoms in the first 2 months after implant. No significant financial relationships to disclose.