Authored by Whitney Stanton*
Introduction
Prostate cancer is the most common form of malignancy and the second leading cause of cancer death in men in the United States. In 2019, approximately 174,650 cases of prostate cancer will be diagnosed [1]. Although a serious disease, most men will not die from prostate cancer. The use of the prostate specific antigen (PSA) blood test and trans-rectal ultrasound guided (TRUS) biopsy have resulted in over-diagnosis and overtreatment of clinically insignificant prostate cancer while also missing high-risk clinically significant tumors [2]. Clinically significant prostate cancer is defined as a lesion with high-grade prostate cancer (Gleason Score ≥ 7) or volume ≥ 0.5 cc. Therefore, it is important to identify men who have clinically significant prostate cancer who would benefit from treatment as well as identify men with low-risk tumors who would benefit from a more conservative approach such as active surveillance.The use of multiparametric magnetic resonance imaging (mpMRI) in conjunction with the Prostate Imaging and Reporting Data System version 2 (PIRADS v2) allows physicians to target lesions in the prostate for biopsy [2]. PIRADS v2 assigns one composite score that indicates risk of clinically significant prostate cancer on mpMRI. A PIRADS score of 3, 4, or 5 designates intermediate, high, or very high risk of clinically significant prostate cancer, respectively. Men with a PIRADS score ≥ 3 are recommended for prostate biopsy, but a PIRADS score ≤ 2 cannot rule out clinically significant prostate cancer. Conventionally, a patient undergoes mpMRI and the urologist uses the mpMRI report to guide prostate biopsies in-office using a real-time urologic ultrasound, which operates at 6-9 MHz. The ExactVu™ Micro-Ultrasound system (ExactVu™ Micro-Ultrasound, Exact Imaging, Markham, Canada) is a new 29 MHz prostate imaging technique which provides a realtime imaging of cancer lesions at a high resolution of 70 microns [3]. In a study comparing high resolution micro-ultrasound imaging to mpMRI, micro-ultrasound imaging provided similar sensitivity to clinically significant prostate cancer as mpMRI. Micro-ultrasound imaging provides a real-time, high-resolution ultrasound platform and can be used to guide prostate biopsies in-office with improved imaging resolution compared to conventional urologic ultrasound, making it more time and cost effective. Herein, we describe our findings of micro-ultrasound imaging compared to preoperative mpMRI for the diagnosis of cancer lesions. Micro-ultrasound was employed as an adjunct in addition to standard-of-care TRUS in four men undergoing primary and salvage cryotherapy.
Discussion
This study received institutional review board approval under COMIRB #19-139. Four patients underwent cryotherapy for treatment of non-metastatic prostate cancer. Each patient had confirmatory TRUS biopsy pathology, three of the four men had prior mpMRI, and all men had micro-ultrasound before, during, and after cryotherapy in addition to the standard-of-care transrectal ultrasound. All cases were performed according to the same surgical protocol and by the same surgeon. Two freeze thaw cycles were completed and were monitored via ultrasound. The entire prostate gland was treated. The cryotherapy probes were placed through the cryotherapy template under ultrasound guidance [4].Case 1
This patient was a 73-year-old male with no family history of prostate cancer. He had previous cyberknife radiotherapy in 2011 for Gleason grade group 3 (4 + 3 = 7) prostate cancer involving seven out of 26 biopsy cores. Cyberknife radiotherapy is a form of imageguided stereotactic body radiation therapy [5]. After cyberknife radiotherapy, his PSA nadired to 0.4 ng/ml, but slowly increased to 2.6 ng/ml prompting a PET-CT scan in August 2018. The PETCT revealed a centrally located focus of increased tracer uptake within the inferior prostate, likely compatible with malignancy. There was no evidence of bony metastases. In September 2018, the patient underwent a 20-core TRUS biopsy and was found to have Gleason grade group 3 (4 + 3 =7) in 1 of 20 cores and Gleason grade group 2 (3 + 4 = 7) in 1 of 20 cores involving 15 and 30% of each core, respectively. The mpMRI demonstrated a 1.6 cm diffusion restricting early enhancing lesion in the central gland near the apex and was concerning for disease recurrence. The prostate volume was 32 cc. During his cryotherapy procedure, three probes were used: two on the left and one on the right. The prostate volume was 49.7 g. The micro-ultrasound identified suspicious lesions bilaterally at the apex, consistent with the mpMRI.Case 2
This patient was a 67-year-old male with history of a urethral stricture. An elevated PSA of 6.77 ng/ml prompted a TRUS biopsy that revealed Gleason grade group 3 (4 + 3 = 7) prostate cancer with multifocal perineural invasion. He had a negative CT of the abdomen and there was no evidence of metastatic disease in the abdomen or pelvis. A mpMRI of the prostate revealed a PIRADS 4 nodule (9 mm hypointense) in the lateral left peripheral zone in the mid aspect of the gland with acute restriction and a PIRADS 3 nodule (2.3 cm) in the anterior left transition zone from mid to base that predominantly had well-circumscribed boundaries, but demonstrated asymmetric enhancement with acute restriction. During his cryotherapy procedure, seven probes were used: four on the left and three on the right. The prostate volume was 50.3 g. The micro-ultrasound clearly visualized seminal vesicle invasion and extra-prostatic extension on left side, consistent with his biopsy findings.
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