Results: Median prostate dimensions in mm and volume in cc with 5 th and 95 th percentiles are as follows: Height by RRP = 30 (24, 45); TRUS prolate = 33 (25, 44); TRUS planimetry = 35 (27, 46); and CT = 42 (34, 52). Width by RRP = 47 (35, 60); TRUS prolate = 50 (42, 61); TRUS planimetry = 51 (42, 61); and CT = 51 (41, 67). Length by RRP = 42 (30, 63); TRUS prolate = 49 (39, 60); TRUS planimetry = 45 (35, 60); and CT = 41 (30, 54). Volume by RRP = 32 (18, 77); TRUS prolate = 41 (24, 79); TRUS planim- etry = 43 (24, 80); and CT = 45 (25, 70). Statistical analysis showed that width and volume measurements were similar across the TRUS and CT cohorts and length measured by CT and RRP was similar. Statistically significant differences (p \ 0.001) were evident when comparing height across all modalities of measurement. Conclusions: While the median TRUS and CT volumes were similar at 41–45 cc, the RRP median volume was approximately 10–13 cc less than the EBRT or PPB groups. Nevertheless and despite differences in measurement methods these data exhibit remarkable similarity in prostate dimensions for the three cohorts. A trans-urethral ultrasound probe having an azimuthal field of view or brachytherapy custom monofilament with a treatment length of 48–55 mm or 54–63 mm would encompass 75% and 95% of the cases examined in this study respectively (Figure). (Research supported by NIH Grants R33 CA107933-01 and CA91956-01G/H.) Author Disclosure: J.L. Leenstra, None; B.J. Davis, None; T.M. Wilson, None; L.A. Mynderse, None; M.G. Herman, None; D.W. Hillman, None; K.L. Allen, None; J.C. Cheville, None; D.R. Holmes, None; B.F. King, None. 2318 Equivalent Uniform Dose (EUD), D 90 , and V 100 Correlation With Biochemical Control After Low-Dose- Rate Prostate Brachytherapy for Clinically Low Risk Prostate Cancer: The Duke Experience E. Miles, A. Alkaissi, S. Das, R. Clough, M. Anscher, J. Oleson Duke University Medical Center, Durham, NC Purpose/Objective(s): To report on the relationship between post-implant dosimetric quantifiers including EUD, D 90 and V 100 , with respect to biochemical relapse free survival (bRFS) in a retrospective review of a cohort of men receiving low-dose-rate pros- tate brachytherapy (LDRPB) at Duke University Medical Center affiliated institutions. It was hypothesized that EUD might give a more meaningful measure of dose to the prostate as a whole. Methods/Materials: This report includes the retrospective review of 140 sequential patients with histologically confirmed, clin- ically localized, prostate cancer treated with LDRPB alone (no external beam therapy or hormonal therapy) from 1997 to 2003 with at least three years of time elapsed since their implant, and at least one year of clinical follow-up. Patients were treated with either 125 I or 103 PD implants performed at Durham Regional Hospital to a prescription dose of 125 Gy with 103 PD and 160 Gy with 125 I (post TG-43) or at the Durham VAMC to a prescription dose of 160 Gy with 125 I (post TG-43). Post implant CT scans were col- lected two weeks after the implant to allow for post-implant dosimetry. Dosimetric quantifiers were calculated from prostate vol- ume and seed positional information. Due to the differences in dose prescription with 125 I from the current standard (160 Gy versus 145 Gy post TG-43) and the two isotopes used for implant, the dosimetric quantifiers were scaled to a prescription dose of 145 Gy with 125 I for comparison purposes. Biochemical recurrence was defined according to the ASTRO consensus definition. Results: The median follow-up time for the cohort was 45 months. The median EUD was 168.8 Gy (range 40.7 to 271.1 Gy). The median D 90 was 137.9 Gy (range 40.6 to 203.2 Gy), with 67 patients (47.9%) having a D 90 . 140 Gy. The median V 100 for 145 Gy was 87.8% (range 43.5% to 99.9%). Proceedings of the 49th Annual ASTRO Meeting S381