PP05  Presentation Time: 9:56 AM: The Performance of Multiparametric MRI in Identification of Intraprostatic Tumor Deposits After Local Prostate Radiation Therapy.

To assess the performance of multiparametric (mp) MRI in identification of intraprostatic tumor deposits in patients previously treated with local radiation therapy (RT) using a systematic and targeted MR-gided transperineal prostate biopsy technique. Thirty patients with a rising PSA and negative metastatic work up after prior external beam RT, brachytherapy, or combined external beam RT and brachytherapy for localized prostate cancer underwent a combined systematic and targeted MRI-guided prostate biopsy using a transperineal approach. For each patient, a pre-biopsy mpMRI scan was obtained and imported into a prostate biopsy planning system. Transverse T2-weighted images were then reoriented from the supine to dorsal lithotomy position. Dividing the prostate into an apical and base section, a systematic array of transperineal biopsies spaced approximately 10mm apart was planned with additional biopsies targeting any mpMRI-identified PI-RADS 3, 4, or 5 lesion. Biopsy procedures were carried out under general anesthesia in the dorsal lithotomy position using a transrectal ultrasound with stepper-stabilizer and template grid. Matching of the planning mpMRI images to live ultrasound images was achieved using the template grid as a reference. All patients successfully underwent biopsy without post-procedure urinary obstruction or infection. The median prostate volume was 36cc (range 12-90, IQR 24-51). The median PSA prior to biopsy was 4.7 ng/mL (range 1.9-24.6, IQR 3.0-7.3). The median number of biopsy specimens obtained per patient was 21 (range 13-34, IQR 17-24). A total of 32 PI-RADS lesions were identified in 30 patients. Overall, the positive predictive value (PPV) of any PI-RADS 3-5 lesion for prostate cancer (based on pathologic confirmation) was 84% (27/32). The individual PPV of PI-RADS 3, 4 and 5 lesions were 40% (2/5), 89% (17/19), and 100% (8/8), respectively. Forty-three percent (13/30) of patients harbored mpMRI-unidentified prostate cancer. Thirty percent (9/30) of patients harbored mpMRI-unidentified GS≥7 disease. Using prostate mpMRI to identify intraprostatic tumor deposits after local radiation therapy results in a high PPV, particularly for PI-RADS 4 and 5 lesions. However, given the high rate of mpMRI-unidentified prostate cancer, the addition of systematic transperineal prostate biopsy information appears necessary to most accurately identify all intraprostatic tumor deposits. These data would suggest that a combination of systematic and mpMRI targeted biopsies are necessary to optimally perform focal salvage therapy in the setting of local recurrence after radiation therapy. [ABSTRACT FROM AUTHOR]