3278 - The Performance of PET, Multiparametric MRI and Transperineal Prostate Biopsy in Identification of Intraprostatic Tumor Deposits after Prostate Radiation Therapy

Purpose/Objective(s):

To assess the performance of PET, multiparametric (mp) MRI and a MR-guided transperineal prostate biopsy technique to identify and localize intraprostatic tumor deposits in patients previously treated with prostate radiation therapy (RT).

Materials/Methods:

Forty-five patients with a rising PSA after prior RT for localized prostate cancer underwent an 18F-fluciclovine or PSMA PET scan followed by mpMRI and MRI-guided prostate biopsy using a transperineal approach. For each patient, pre-biopsy mpMRI images were imported into a prostate biopsy planning system. 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.

Results:

Median time from completion of initial course of RT to biopsy was 6.2 years (interquartile range IQR 4.1-9.8). Median prostate volume was 28cc (IQR 23-36). Median PSA prior to biopsy was 2.8 ng/mL (IQR 1.9-4.4). Median number of biopsy cores obtained per patient was 18 (IQR 16-20). On a per lesion basis, the overall positive predictive value (PPV) of PET scans was 85% (35/41). The PPVs of the 18F-fluciclovine and PSMA scans were 73% (8/11) and 90% (27/30), respectively. A total of 39 PI-RADS lesions were identified on mpMRI. The PPV of any PI-RADS 3-5 lesion for prostate cancer (based on pathologic confirmation) was 85% (33/39). The individual PPVs of PI-RADS 3, 4 and 5 lesions for prostate cancer were 50% (3/6), 86% (19/22), and 100% (11/11), respectively. For lesions that co-localized on both mpMRI and PET, the PPV of the combined scans was 91% (32/35). Twenty-seven percent (12/45) of patients harbored biopsy-proven prostate cancer that was not identified by either PET or MRI scan. Based on pathologic review, 85% (29/34) of patients had recurrent tumor that localized to a positive area on their pretreatment biopsy. In addition, 85% (29/34) of patients had higher grade disease on recurrence compared to their pretreatment biopsy.

Conclusion:

In patients with prior prostate RT, an intraprostatic lesion is highly likely to be cancerous on biopsy if it is positive on either PET or mpMRI; the likelihood further increases if it is positive on both scans. In addition, recurrent tumor is likely to be in a similar location but of higher grade compared to original diagnosis. Given the significant rate of unidentified prostate cancer by either scan, the addition of systematic transperineal prostate biopsy appears necessary to most accurately identify all intraprostatic tumor deposits.