252 Background: Concordance between intraoperative and postoperative dosimetry is a well-known marker of implant quality in prostate brachytherapy. The aim of the study was to evaluate if the use of variable distance strand seeds allows an improvement in the quality of the post implantation dosimetry. Methods: Before December 2010, an iodine 125 loose-seed technique was used for prostate brachytherapy. Since this date, patients have been treated with new variable distance strand seeds (ProLink; Bard). Post implant dosimetry was compared to intraoperative dosimetry in 30 patients treated with loose seeds and 29 patients treated with strand seeds. The prescribed dose was 145Gy. Variations of dosimetric parameters were used to set the two techniques against one another: prostate V100 and D90 and rectum V145 and V160. Results: There was a significant difference between intraoperative and postoperative V100 and D90 for all 59 patients: V100 preop-postop: mean 6,65% +/- SD 4,5; D90 preop-postop: 18,73Gy +/- SD 15 (p<0,0001). This dosimetric difference between pre and post-operative dosimetry is more important using loose seeds brachytherapy: V100 preop-postop: 9,5% +/- SD 4,1 vs 3,7% +/- SD 2,7 for loose seeds and strand seeds respectively (p<0,0001), and D90 preop-postop: 27,9Gy +/-SD 13,6 vs 9,2Gy +/- SD 9,7 for loose seeds and strand seeds respectively (p<0,0001). For V145 rectum and V160 rectum, dosimetric difference wasn't significant: V145 rectum preop-postop: -0,9% +/- SD 1,4 with stranded seeds vs. -1,6% +/- SD 2,1 with loose seeds (p=0,14) and V160 rectum pre-postop: -0,5% +/- SD 0,8 with strand seeds vs. -0,5% +/- SD 0,8 with loose seeds (p=0,16). Conclusions: Stranded seeds implantation increases the quality of implantation by reducing the dosimetric difference (V100 and D90) between intra and post-operative dosimetry to a maximum of 6% and 7% vs. more than 20% with loose seed implantation. Moreover, this technique doesn’t seem to modify the risk of rectal toxicity. This achievement in implantation and dosimetric quality might lead to a gain in clinical results.