Assessment Of Multiparametric Magnetic Resonance Imaging For The Detection Of Local Recurrence After Low-Dose-Rate Brachytherapy

Multiparametric MRI (mpMRI) has improved detection and risk stratification of men with newly diagnosed prostate cancer. mpMRI has recently been explored in the setting of biochemical recurrence after external beam radiation therapy and High Dose Rate brachytherapy. However, mpMRI is not routinely performed in the setting of biochemical relapse after Low Dose Rate (LDR) brachytherapy because of concern for seed-induced MRI artifact. Herein, we report the first series of post-LDR brachytherapy mpMRI and confirmatory biopsy in the setting of PSA relapse. All patients who received LDR brachytherapy as a component of therapy and were referred to our institution for mpMRI following PSA relapse were analyzed (2011-present). mpMRI consisted of endorectal coil T2 weighted imaging (T2W), dynamic contrast enhanced (DCE) imaging, and diffusion weighted imaging (DWI) sequences with apparent diffusion coefficient (ADC) maps. Lesions were categorized as suspicious by a prostate-dedicated radiologist based on detection in each sequence. Biopsy was performed in patients with no evidence of metastases. Biopsy-proven lesions without unilateral mpMRI findings were considered false negative identifications by mpMRI. Sensitivity (SN) and positive predictive value (PPV) of mpMRI in detecting biopsy-confirmed lesions was determined. 20 patients who developed recurrence post-brachytherapy (Phoenix Criteria: n = 19, rapid PSA rise: n = 1) were included. The mean PSA at the time of mpMRI was 6.42 ng/ml. Pre-implant Gleason score was ≤6 in 12 patients and >6 in 8 patients. The median time from implant to recurrence was 62 months. Prostate biopsy was performed in 17 patients (n = 3 excluded due to metastases). mpMRI detected at least one suspicious prostate lesion in 15/17 patients. A total of 25 lesions were identified (0-4 per patient), 16 of which were confirmed pathologically in 12/17 patients. Pathologic evidence of recurrence was concordant with mpMRI in 12/13 patients. Pathologically confirmed tumors identified by mpMRI were frequently located in the transition zone (TZ, 43.75%) and seminal vesicles (SV, 37.5%). 2/16 of TZ lesions were anterior to the urethra. Two pathologically confirmed SV lesions were not identified by mpMRI. Nine mpMRI defined lesions were benign on biopsy. The overall SN and PPV of detecting pathologically confirmed lesions on any parameter of mpMRI was 70% and 64% respectively. mpMRI detection of local recurrence in the setting of biochemical failure after prostate brachytherapy is feasible, with a high tissue-concordant cancer detection rate. The pattern of local recurrence in the TZ and in the SV post-brachytherapy should be validated in larger series, as it may have implications for treatment planning.