A comparison of the precision of seeds deposited as loose seeds versus suture embedded seeds: a randomized trial

Brachytherapy for prostate cancer with permanent low-dose-rate seeds has been shown to be an effective treatment for early stage prostate cancer. Due to the rapid falloff of dose, accurate seed placement is critical for optimal dosimetry. One approach to achieve optimal dosimetry is the use of seeds embedded in suture material. Seeds embedded in suture may not move after implantation as much as loose seeds. This would improve implant dosimetry. To evaluate this hypothesis a formal study was conducted in which half the gland was implanted with seeds embedded in suture and half with loose seeds. Final dosimetry is compared between both halves of the prostate.

Patients entered this Investigational Review Board approved prospective trial after completion of informed consent. At time of implant, the side of the gland to be implanted with loose as opposed to suture embedded seeds was randomly assigned. The patients then underwent intraoperative preplanned implantation. None of the preplans directed seed locations outside the prostate. Both the seeds embedded in suture and the loose seeds were implanted using needles with stylettes. At 4-6 weeks post implant, seed location was determined with CT. Both sides of the gland on CT were contoured and used for final dosimetric calculations. A cost function analysis was used to determine individual seed position deviation from intended to actual seed location.

Eight patients were enrolled in the study. A total of 549 seeds were implanted; 240 seeds embedded in suture and 309 loose seeds. Prostate volumes ranged from 24.0-45.5 cc with a mean of 38.6 cc. The average radial deviation of the loose seeds from planned position was determined to be 3.1 mm compared with the average radial deviation of the suture embedded seeds of 3.7 mm. There was no improvement in the final dosimetry when suture embedded seeds where used. The D90 and V100 values for the half of the prostate implanted with suture embedded seeds were 71-140 (mean, 92.1) and 80.2-99.5 (mean, 89.6), respectively, for the half of the prostate implanted with loose seeds. (All D90, V100 values are % of prescription dose.)

Seeds embedded in suture material do not lead to superior precision in seed deposition when compared with loose seeds, when implanted inside the prostate.