World Congress of Brachytherapy 2012 S 81 Conclusions: In general, plans with higher individual seed activities result in larger total activity values for a given prostate volume. This trend holds when the activity is normalized to the PTVD(90%). Furthermore, the Wu et al. nomogram overestimates the total activity needed for planning with lower activity seeds and may underestimate the activity needed for planning with higher activity seeds. These results imply that nomogram predictions of total activity should be modified based on the individual seed activity. Modification of the nomogram for low volume, low activity-per-seed implants could reduce the number of seeds ordered by as much as 15-20%, which may achieve a cost-savings of over $100 per implant. PO-200 V150 PREDICTS ERECTILE OUTCOME IN PATIENTS UNDERGOING LOW- DOSE-RATE (LDR) BRACHYTHERAPY ALONE FOR PROSTATE CANCER M.A. Kollmeier 1 , L.M. Scala 1 , D. Kunaprayoon 1 , N. Mathur 1 , G. Cohen 1 , X. Pei 1 , Z. Zhang 2 , J. Mulhall 3 , B. Cox 1 , M.J. Zelefsky 1 1 MSKCC, Radiation Oncology, New York NY, USA 2 MSKCC, Biostatistics, New York NY, USA 3 MSKCC, Urology, New York NY, USA Purpose/Objective: To identify dosimetric predictive factors for erectile dysfunction (ED) after LDR brachytherapy as monotherapy. Materials and Methods: Of 1013 patients treated with LDR prostate brachytherapy as monotherapy at our institution, 75 patients who were potent at baseline, ≤65 years old and had a minimum follow-up of 2 years were included in this analysis. Potency was as defined by an International Index of Erectile Function (IIEF) score of ≥ 22 or by physician documentation. Patients taking oral phosphodiesterase inhibitors pre-implant were excluded. Patients who received androgen deprivation therapy or supplemental external beam radiotherapy were excluded. All patients underwent a real-time transperineal ultrasound-guided permanent prostate implant with either I-125 or Pd-103. The prostate, rectum, urethra, bladder, penile bulb, bilateral proximal penile crura, and bilateral neurovascular bundles were contoured on day 0 post-implant dosimetry CT scan. Dosimetric endpoints evaluated included the mean dose, minimum dose and D30 to the crura (right, left and combined), penile bulb, neurovascular bundles (right, left and combined) as well as the prostate V150, V100 and D90. Prostate volume, age, vascular comorbidities (coronary artery disease, diabetes, hypertension, dyslipidemia, tobacco use) were also recorded. Erectile function was assessed at last follow-up with the IIEF questionnaire. Median follow-up was 34.3 months. Cox regression was used for univariate and multivariate analysis. Survival curves were generated by the Kaplan-Meier method and compared using the log-rank test. The Bonferroni correction was used to account for multiple comparisons. Results: At last follow-up, 71% (n=53) of patients were potent and 29% (n=22) developed erectile dysfunction (ED). On univariate analysis, higher prostate D90, V100, and V150 were significant predictors of ED (p=0.0078, p=0.019, and p=0.0007, respectively). On multivariate analysis, both pre-implant prostate volume and V150 were significant predictors of ED (p=0.09 and p=0.001, respectively). Hazard ratio for post-brachytherapy potency in patients with V150 ≤60% versus >60% was 4.01 (95% CI: 2.02 -7.97), p<0.0001. Point estimates for survival without ED at 3 years were 89% (95% CI: 80% - 99%) and 33% (95% CI: 18%-60%) in patients with V150 ≤ or > 60%, respectively. Conclusions: In this carefully selected patient cohort, prostate V150 was a strong predictor for post-implant ED. We could not identify a correlation between dose to erectile structures (penile crura, neurovascular bundles, or penile bulb) and subsequent ED. We recommend limiting the V150 to the prostate to less than 60% on day 0 post-implant CT in an effort to reduce the risk of post implant ED. PO-201 INSTITUTIONAL ANALYSIS OF OUTCOMES FOR STAGES T1-T2 PROSTATE CANCER TREATED WITH BRACHYTHERAPY A. Soares 1 , L. Trigo 2 , L. Carvalho 2 , A. Pereira 3 , T. Viterbo 3 , R. Henrique 4 , J. Matos 4 , C. Castro 1 , A. Oliveira 1 , J. Oliveira 5 1 Instituto Português de Oncologia do Porto, Radiotherapy Department, Porto, Portugal 2 Instituto Português de Oncologia do Porto, Brachytherapy Department, Porto, Portugal 3 Instituto Português de Oncologia do Porto, Department of Medical Physics, Porto, Portugal 4 Instituto Português de Oncologia do Porto, Department of Pathology, Porto, Portugal 5 Instituto Português de Oncologia do Porto, Urology Department, Porto, Portugal Purpose/Objective: To evaluate the casuistry of an institution and to assess biochemical progression-free survival (bPFS) outcome after permanent prostate brachytherapy (BT). Materials and Methods: We analyzed the first 118 patients treated in our institution, between June 2004 and December 2006, with permanent interstitial BT for T1-T2 prostate cancer. All patients were treated with Iodine 125 ( 125 I) (median prescribed dose of 145 Gy). The pos-implant computed tomography (CT)-based dosimetry was made around 4 weeks after BT. The median follow-up was 71 months. Multiple clinical, treatment and dosimetric parameters were evaluated for impact on survival parameters. Samples from diagnostic biopsies of patients that presented biochemical progression were reviewed. Results: The median age at diagnosis was 66 years (45-76). The pre- implant PSA ranged between 1.22 and 11.87 ng/ml (median 6.48 ng/ml). Of the whole sample, 89% presented with no lower urinary tract symptons (LUTS). The AJCC clinical stage T1c was the most frequent (70 patients, 59.3%), followed by the T2a (43 patients, 36.4%). The most common Gleason score was 3+3 (85.6%). Fourteen patients (11.9%) received neoadjuvant hormone therapy. The pos- implant CT-based dosimetry revealed that the implanted volume varied from 13.7 to 65 cm 3 (median 30.3 cm 3 ); the D-90 was >130Gy in 85 (72%) patients and the V100 / V150 ranged between 57% – 99.4% (median 87.9%) / 19.6 – 71.3% (median 46.5%); the D2ccbladder varied from 20 to 115Gy and the D2ccrectum from 35 to 150Gy. The main toxicity referred was dysuria – 57 (48.3%) patients with grade I, 37 (31.4%) with grade II and only 1 patient with grade III. About 25% of all patients referred erectile dysfunction (66.7% of whom had >60 years). During follow-up, 53 (46.5%) patients presented a PSA bounce phenomenon. Eleven (9.3%) patients presented biochemical progression, of which 2 were submitted to prostatectomy and 9 to hormone therapy. Revision of diagnostic specimens revealed an upgrade Gleason score in 4 patients. The bPFS at 5 / 7 years was 93% / 90%.