A comparison of preplan transrectal ultrasound with preplan-CT in assessing volume and number of seeds needed for real-time ultrasound-based intra-operative planning in prostate ¹²⁵I seed implantation

Abstract 

Purpose

Intra-operative (real-time) treatment planning has been adapted by many institutions for low–dose rate prostate brachytherapy. Although this allows dosimetric planning to be done during the procedure, preplan imaging to obtain a prostate volume is essential to identify the number of seeds to ensure adequate volume coverage. Currently, there is no consensus regarding the most appropriate imaging to obtain this information. We conducted a retrospective study to compare how volumes obtained from preplan CT (p-CT) scans or preplan transrectal ultrasound (p-TRUS) correlated with real-time ultrasound and postimplant CT volumes and the difference in accuracy of seed estimation between these techniques.

Methods and Materials

Ninety-two patients underwent ¹²⁵I permanent seed implants at Thomas Jefferson University Hospital between February 2002 and August 2008. Fifty-one patients underwent p-TRUS before intra-operative planning and 41 patients were evaluated by p-CT.

Results

The median difference in volume between preimplant imaging and the intra-operative planning ultrasound was 3.59 and 5.2cc for patients who underwent p-TRUS and p-CT, respectively. p-TRUS volumes more closely correlated with real-time intra-operative volumes (R=0.84 in all patients and R=0.91 in hormone-naïve patients) vs. p-CT (R=0.82). The median number of seeds wasted using p-CT was 18 vs. 7 using volumes derived from p-TRUS.

Conclusions

The number of seeds ordered could be more accurately obtained from p-TRUS volumes, and this translated into less seed wastage. Our findings indicate that p-TRUS is a more accurate and an economically superior alternative to p-CT imaging in the era of real-time ultrasound planning.

Keywords: Intra-operative planning, Preplan imaging, Prostate brachytherapy