Reduction of seed motion using a bio-absorbable polymer coating during permanent prostate brachytherapy using a mick applicator technique

The addition of a braided bio-absorbable vicryl coating to the surface of radioactive seeds used for low dose rate (LDR) prostate brachytherapy is intended to reduce the incidence of seed movement and migration. Here, we present a single-institution study of the frequency and severity of seed slippage (initial seed movement) of coated seeds in comparison with uncoated seeds.

Forty-seven patients received permanent prostate brachytherapy, with either coated (n = 26) or uncoated (n = 21) seeds. AgX100 ¹²⁵ I seeds, coated or uncoated, and uncoated Model 200 ¹⁰³ Pd seeds were used. During the ultrasound-guided implantation procedure, each implanted seed was categorized as having remained in the implanted position after being placed, having moved slightly, or having left the ultrasound field of view.

3.1% of the coated seeds (AgX100 seeds, n = 70) and 6.9% of the uncoated seeds (AgX100 and Model 200 seeds, n = 128) were observed to have moved at least 2 mm from their initial implant positions, respectively. The difference in incidence of this movement was 54.4% (P = 0.0026). Coated AgX100 seeds demonstrated a 66.7% lower rate of movement of at least 2 mm than that for uncoated AgX100 seeds (P = 0.038), and a 49.0% lower rate than that for Model 200 seeds (P = 0.021). While no significant differences were noted in prescription dose coverage of the prostate or the studied dosimetric parameters for the organs at risk between the coated and uncoated seeds (P > 0.05) in the CT-based Day-0 postoperative plans, the limited sample size and differences in energies between the ¹²⁵ I and ¹⁰³ Pd seeds make further analysis of postoperative dosimetric coverage difficult without additional data directly comparing the coated and uncoated ¹²⁵ I seeds.

When the vicryl coating is used, seeds have a significantly lower propensity to slip from their initial implant locations. This may help maintain dosimetric integrity, warranting further study of postoperative dosimetry.