All treatment plans used a prescription dose of 145 Gy with 125I sources and aimed to satisfy the following dosimetric parameters: percentage

of PTV receiving 100% of the prescription dose (PTV V100) >95%, percentage of PTV receiving 150% of the prescription dose (PTV V150) <60%, percentage of PTV receiving 200% of the prescription dose (PTV V200) <20%, rectal volume receiving 100% of the prescription dose (R100) <1 cm3, and urethral volume receiving 200% of the prescription dose (U200) to be near 0. All patients underwent permanent interstitial prostate implants, and intraoperative TRUS BMS 777607 was used to guide needle placement and verify the positioning of the strands. In addition to CT scans on Day 0 and Day 30 after the implant, all patients underwent sMRI on postimplant Day 30. For the purposes of the present study, the preimplant

erMRI and 30-day postimplant sMRI images were used to retrospectively replan the seed placement for each patient. The T2-weighted series for both the erMRI and sMRI were imported into the VariSeed system. Contours for the prostate, bladder, rectum, urethra, and seminal vesicles were outlined independently on the erMRI and sMRI. All contours were approved by the two reviewers. The PTV was defined in the same way as for the actual treatment, as a 3-mm expansion from the Dorsomorphin in vitro prostate anteriorly and laterally, a 5-mm expansion cranially and caudally, and no expansion posteriorly. The erMRI- and sMRI-based Thymidylate synthase plans were jointly developed by a medical dosimetrist and radiation oncologist who were blinded to the TRUS-based plans; they used the same standard modified peripheral loading technique as that used for TRUS-based plans, optimized to the anatomic detail visible on the MRI. Planning was

done independently for both erMRI and sMRI. All MRI-based treatment plans were designed to satisfy the same dosimetric parameters as those used in the actual treatments: PTV V100 >95%, V150 <60%, V200 <20%, R100 <1 cm3, and U200 near 0. Prostate volume and dimensions, the radioactivity-to-prostate-volume ratio, and dosimetric parameters (PTV V100, V150, V200; dose to 90% of the prostate [D90]; R100; U200) were compared for the three modalities (TRUS, erMRI, and sMRI) by using the Wilcoxon signed-rank test for paired samples. Comparisons were performed pair wise between each of the MRI modalities and TRUS. All p-values were obtained by using two-tailed tests, and a p-value of <0.05 was considered statistically significant. Data were analyzed with PASW Statistics 17.0 (SPSS, Inc., Chicago, IL). To determine whether the different imaging modalities resulted in differences in the visualized anatomy of the prostate, the mean prostate volume and dimensions measured by TRUS, erMRI, and sMRI were compared (Table 1). When compared with TRUS, the mean prostate volume measured by erMRI was smaller (29.5 vs. 32.5 cm3 by TRUS, p = 0.001), the mean medial-lateral diameter was larger (5.01 erMRI vs. 4.