The dosimetric quality of brachytherapy implants in patients with small prostate volume depends on the experience of the brachytherapy team

Abstract 

Purpose

To investigate the dosimetric outcome of brachytherapy in patients with small prostate volume (PV).

Methods and Materials

Forty-three patients with small PV (<25cm³) as determined using transrectal ultrasound and 120 patients with non–small PV (>25cm³) that had received ¹²⁵I seed implants were reviewed in a retrospective cohort study. Implantations were performed under transrectal ultrasound guidance, and the prescription dose was 145Gy. A CT and MRI scan of the pelvis were performed 1 month after implantation for dosimetric study.

Results

Compared with non–small PV patients, patients with small PV experienced larger 1-month edema (p<0.001); lower dose to 90% (the isodose enclosing 90% of PV and representing a minimum dose to that volume of the prostate [D₉₀]) of the prostate (p=0.03); higher intracapsular seed density (p<0.001); and were less likely to achieve D₉₀≥140Gy (p=0.013) in a postimplant dosimetric study. The number of patients with D₉₀<140Gy decreased steadily in both subsets of patients as the implant program matured (odds ratio=0.56 per year, p<0.001), but the small prostate group exhibited more improvement compared with the non–small prostate patients over the same time period. Multivariate analysis revealed that brachytherapy team experience rather than the size of prostate was a more important predictive factor of implant quality (p<0.001).

Conclusions

This single institution experience demonstrated a significant learning curve in the initial years of a prostate brachytherapy program, especially for patients with small prostates. A small prostate itself is not a contraindication of brachytherapy. The quality of implant for patients with small prostates depends more on the skill of the brachytherapy team.

Keywords: Prostate, Brachytherapy, Dosimetry