e112 THE JOURNAL OF UROLOGY� Vol. 191, No. 4S, Supplement, Saturday, May 17, 2014

with suspicious findings, 53 were false positives. Univariate andmultivariate analyses failed to demonstrate any significant cor-relation between type of surgery, pathology, and frequency ofroutine imaging.

CONCLUSIONS: A large number of follow-up imaging studieswere performed despite a low recurrence rate. There was a high rate ofroutine abdominal imaging with no evidence of disease. No clinico-pathologic criteria were identified that were predictive of imaging fre-quency. Given the low likelihood of finding disease recurrence withincreased imaging, these findings support adherence to publishedguidelines for routine surveillance imaging.

Source of Funding: None

MP12-17VARIABILITY OF PIXEL BRIGHTNESS INTENSITY CAN BE USEDTO FURTHER CHARACTERIZE A STONE’S COMPOSITION

Yaniv Larish*, Leonard Glickman, Jay A. Motola, New York, NY

INTRODUCTION AND OBJECTIVES: Non-contrast CT(NCCT) is the gold standard of imaging in the diagnosis of urinarycalculi. Composition of stones can be determined based on a stone’spixel brightness intensity as measured by mean Hounsfield units (mHU)with varying degrees of certitude. In this study, we sought to evaluatethe variability of pixel intensity by measuring the standard deviation ofHU values (HUsd) within specific stone types to improve the accuracy ofdetermining a stone’s composition.

METHODS: A single-institution, retrospective, chart reviewwas performed from June 2009 to July 2013 identifying patients withGU calculi. All patients had a NCCT scan of the abdomen and pelviswhich confirmed the presence of a GU stone. All calculi were treatedwith endoscopic management during which stone specimen wasretrieved for analysis. Stone composition was determined by infraredspectroscopy. CT scans were reviewed by two urologists whowere blinded to the stone’s chemical composition. The radio-graphic characteristics of the stone, including mHU and HUsdwere measured.

RESULTS: 155 patients with 191 distinct stone episodes wereidentified. Patients with multiple stones in a single renal unit wereexcluded from analysis. The mean time between CT scan and surgerywas 27 days. 72%, 17%, 6%, and 5% of the stones were composed ofcalcium oxalate (CaOx), uric acid (UrA), calcium phosphate (CP), andcystine (CY), respectively. Inter-rater reliability demonstrated goodagreement between the two reviewers (r¼0.89 and 0.74 for mHU andHUsd respectively). The mHU values were 697.78, 425.83, 706.86, and634.67 for CaOx, UrA, CP, and CY, respectively. There was a signifi-cant difference when comparing UrA to each of the other three stonetypes: CaOx, CP, and CY (p<.0001, 0.0028, 0.0482, respectively). TheHUsd values were 126.22, 61.56, 128.22, and 60.16 for CaOx, UrA, CP,and CY, respectively. There was a significant difference comparing UrAto CaOx and to CP (p<.0001, 0.0008, respectively) and a significantdifference comparing CY to CaOx and to CP (p¼ 0.0001 and 0.0034respectively).

CONCLUSIONS: The HU information obtained from CT scanshas been limited to the mHU number. The HUsd is a previously ignoredand readily obtainable variable that should be used to increase theclinician’s confidence in determining a stone’s composition and guid-ing treatment.

Source of Funding: None

MP12-18FOCAL THERAPY FOR PROSTATE CANCER: THE UTILITY OFA CONFIRMATORY TRANSPERINEAL TEMPLATE GUIDEDPROSTATE BIOPSY TO IDENTIFY APPROPRIATECANDIDATES

Khanh Pham*, Claudio Jeldres, John Corman, Katherine Odem-Davis,Erika Wolff, Christopher Porter, Seattle, WA

INTRODUCTION AND OBJECTIVES: Focal Therapy (FT) isconsidered a promising potential treatment option for men with low riskprostate cancer (CAP). FT may not be suitable for men with high vol-ume, multifocal and high Gleason (GL) grade disease. The currentstandard to determine low risk CAP is 12-core transrectal ultrasoundprostate biopsy (TRUS BX). We had 2 aims: 1. Determine the accuracyof a confirmatory staging 24-core transperineal template guided pros-tate biopsy (TP BX) 2. Evaluate the efficacy of TP BX to identify can-didates for FT.

METHODS: For both aims we used an IRB approved pro-spective database to evaluate 172 men who underwent 24-core TPBX between 1/2009 and 8/2013. For Aim 1: Men with CAP whounderwent 24-core TP BX and were treated with RP were evaluated.For Aim 2: Men who were candidates for FT based on an initial12-core TRUS BX that demonstrated NCCN guideline low risk(cT1-2a, GL grade 6, PSA < 10), unifocal (< 2 positive cores) CAPwere evaluated. Confirmatory 24-core TP BX was performed 3months after initial TRUS BX under anesthesia using gray scaleTRUS combined with the brachy-stepper device. The templateincluded 12 cores obtained from the anterior prostate (base, midand apex) together with 12 posterior lateral cores (base, midand apex).

RESULTS: For Aim 1: 25 men had TP BX followed by RP. GLgrade at TP BX significantly agreed with RP for 21/25 men; accuracy ¼0.8 (95% CI: 0.59, 0.93; p¼0.004). At RP, 23/25 men had anteriortumor (AT). TP BX sensitivity to RP detection of AT ¼ 0.57 (95% CI:0.34, 0.77; p¼0.67). For Aim 2: 46 men met inclusion criteria.Following TP BX: 16 men demonstrated upgraded pathology with anestimated risk of 0.35 (95% CI: 0.21, 0.50), 20 men had increasedvolume of disease with an estimated risk of 0.44 (95% CI: 0.29, 0.59)and 30 men had multifocal tumors with an estimated risk of 0.65 (95%CI: 0.50, 0.79). Table 1 lists detailed results of TP BX. All 23 men(50%) with upgraded pathology or increased volume also had multi-focal tumors detected.

CONCLUSIONS: Our analysis of carefully performed TP BX inmen eligible for FT by TRUS BX indicates that TP BX accurately in-dicates GL Grade (0.8), and up to 50% of patients considered for FThave more aggressive multifocal CAP. While our results requireconfirmation in larger series, we believe TP BX may be important inmen considering FT for low risk CAP.