Rapid strand™ vs. loose (iodine-125 seeds): A prospective randomized trial

Abstract

Cure rates in the treatment of early stage prostate cancer with permanent interstitial brachytherapy are dependent on the delivery of adequate radiation doses to the prostate planned target volume. Successful post-implantation dosimetry is reliant upon the accuracy of seed placement and the ability to prevent seed migration and seed loss. The use of stranded radioactive seeds may decrease seed loss and migration in comparison to loose radioactive seeds. Fifty patients with 1997 AJCC clinical stage T1c-T2a prostate carcinoma were prospectively randomized to implantation with RAPID Strand I125 seeds (RS) (Amersham, Chicago, IL) vs. loose I125 seeds (LS) (Amersham, Chicago, IL). Isotope implantation was performed with standard techniques, using a preplanned modified peripheral loading pattern. CT and MR imaging, and anterior pelvic plain films were obtained on postimplant day 0 (D0) and day 30 (D30). Post-implant dosimetry was performed with a Varian treatment planning system on day 0 and day 30, with manual seed identification and redundancy check. Prostate volumes were contoured using CT and MR fusion. Seed loss and standard dosimetric parameters were compared on day 0 and day 30 between patients treated with RAPID Strand seeds to those treated with loose seeds. Patient characteristics were similar in both treatment groups. A statistically significant difference occurred in patients loosing seeds between RAPID Strand and loose seeds 16% vs. 48% respectively (p = 0.02). A significant difference occurred in patients loosing > 1 seed, 32% (LS) and 4% (RS) (p = 0.03), and in >2 seed loss 24% (LS) and 0% (RS) (p = 0.01). Of patients loosing seeds a statistically significant difference occurred in the number of seeds lost with a mean 2.5 seeds lost (LS) vs. 1.3 (RS) (p = 0.03). The mean D0 V100 was 96% (LS) and 94% for (RS) (p = 0.5). The mean D30 V100 was 94% (LS) and 91% (RS) (p = 0.2). In patients loosing seeds the mean D0 V100 was 94% (LS) and 97% for (RS) (p = 0.09). The mean D30 V100 was 93% (LS) and 94% (RS) (p = 0.9). RAPID Strand I125 seeds demonstrated a statistically significant lower rate of seed loss in comparison to loose seeds in patients undergoing interstitial transperineal prostate brachytherapy. Additionally stranded seeds resulted in a statistically significant decrease in the number of seeds lost per patient when seed loss occurred. Although no statistically significant overall difference was seen in dosimetric parameters between the treatment groups, an increase in day 0 and day 30 V100 was seen in patients loosing seeds favoring (RS).