An analysis of the relation between physical characteristics of prostate I-125 seed implants and lower urinary tract symptoms: bladder hotspot dose and prostate size are significant predictors.

Purpose: Lower urinary tract symptoms are frequently observed after I-125 seed implantation of the prostate. More knowledge about causes and predictors is necessary to be able to develop less toxic implantation techniques. The aim of this study was to identify implantation related factors that contribute to post-implant urinary morbidity.

Materials And Methods: Analysed was a group of 72 patients that filled in a symptom score questionnaire before, 3 months and 6 months after implantation as well as a group of 15 patients that suffered from acute urinary retention. Several dose-volume parameters of prostate, urethra and bladder wall were determined based on a post-implant TRUS-CT scan.

Results: The dose to a 1cm(3) hotspot in the bladder wall (D1cc-bl) as well as the prostate volume were independently correlated with urinary morbidity symptom scores at 3 months (p=0.006 and p=0.005, respectively) and at 6 months (p=0.001 and p=0.015, respectively) after implantation. The number of implanted seeds and the D1cc-bl were significant discriminators (p<0.001 and p=0.015, respectively) for either mild or severe early urinary morbidity.

Conclusion: Bladder hotspot dose appears to be an important dosimetric predictor for urinary morbidity both at 3 months and at 6 months after implantation. Other predictors are prostate volume, or equivalently, the number of implanted seeds.