Loose versus stranded seeds in permanent prostate brachytherapy: dosimetric comparison of intraoperative plans

Abstract

Purpose: To compare target volume coverage and critical organ dosimetry of intraoperative treatment plans for loose seed (LS) and stranded seed (SS) (125)I permanent implants for low and intermediate risk prostate cancer.

Methods: Two hundred and five patients who underwent permanent seed brachytherapy were included in the study. For prostate dosimetry V90, V100, V150, V200, D90 and COIN were used. The dose to urethra and rectum was determined by the maximal dose and relative doses that cover specified volumes. Means and standard deviations were calculated and statistically compared.

Results: On average, 54 (range, 30-78) and 48 (range, 31-67) seeds were implanted in the prostate with individual median activities of 0.62 U (range, 0.52-0.70 U) and 0.71 U (range, 0.65-0.71 U) for LS and SS technique, respectively. The target coverage was slightly better with SS (V100: 98% vs. 96%,p < 0.05; D90: 172 Gy vs. 166 Gy, p < 0.05), but more conformal dose distributions were observed with LS (COIN: 0.70 vs. 0.63, p < 0.05). The dose homogeneity did not differ significantly between the two groups. Regarding the dose to urethra and rectum all dose parameters were significantly lower with LS.

Conclusions: LS resulted in less dose to the urethra and rectum compared to SS in intraoperative dosimetry. A slightly better target volume coverage with decreased conformity of dose distribution is reported with SS. More studies are necessary to determine how these results will affect postoperative dosimetry, and ultimately, clinical outcome.

Keywords: Intraoperative planning; Loose and stranded seeds; Prostate brachytherapy; Seed dosimetry.