Randomized trial of high- and low-source strength ¹²⁵I prostate seed implants

Abstract 

Purpose

A range of ¹²⁵I isotope activities is used in permanent prostate implants. In this study, we compared the implant quality and cost in patients randomized to high-source or low-source strength permanent implants.

Methods and materials

Forty patients were randomized to receive high (0.76 μGy/m²/h) or low (0.4 μGy/m²/h) seed strength implants. The two treatment arms had a comparable mix of primary and boost patients and underwent implantation by the same team. The postimplant dosimetric evaluation was performed using CT (seed position) and T₂-weighted MRI (prostate) scans registered using mutual information techniques. The implant quality parameters were assessed by dose indexes (ratio of achieved dose to planned dose) to quantify the relative error tolerance.

Results

The high-source strength implants had better dose coverage as defined by the dose index; a larger percentage of volume receiving 100% of the prescribed dose as determined by CT (V₁₀₀) (96.3% ± 3.5% vs. 90.4% ± 5.3%; p <0.002); lower seed cost ($2400 vs. $3840 average/case); and took less operating room time on average (67 ± 16 min vs. 85 ± 20 min; p <0.004). Finally, the differences in the rectal and urethral doses were not statistically significant between the two treatment arms.

Conclusion

All 40 patients received an excellent implant as indicated by the CT V₁₀₀. Unless long-term toxicity differs, high-source strength seed implants improve the probability of excellent implant quality and decrease the average cost of permanent prostate implants.

Keywords:  Prostate brachytherapy, MRI dosimetry, Seed strength