Multiparametric Magnetic Resonance Imaging for Active Surveillance of Prostate Cancer

Abstract

Active surveillance has gained popularity as an acceptable management option for men with low-risk prostate cancer. Successful utilization of this strategy can delay or prevent unnecessary interventions - thereby reducing morbidity associated with overtreatment. The usefulness of active surveillance primarily depends on correct identification of patients with low-risk disease. However, current population-wide algorithms and tools do not adequately exclude high-risk disease, thereby limiting the confidence of clinicians and patients to go on active surveillance. Novel imaging tools such as mpMRI provide information about the size and location of potential cancers enabling more informed treatment decisions. The term "multiparametric" in prostate mpMRI refers to the summation of several MRI series into one examination whose initial goal is to identify potential clinically-significant lesions suitable for targeted biopsy. The main advantages of MRI are its superior anatomic resolution and the lack of ionizing radiation. Recently, the Prostate Imaging-Reporting and Data System has been instituted as an international standard for unifying mpMRI results. The imaging sequences in mpMRI defined by Prostate Imaging Reporting and Data System version 2 includes: T2-weighted MRI, diffusion-weighted MRI, derived apparent-diffusion coefficient from diffusion-weighted MRI, and dynamic contrast-enhanced MRI. The use of mpMRI prior to starting active surveillance could prevent those with missed, high-grade lesions from going on active surveillance, and reassure those with minimal disease who may be hesitant to take part in active surveillance. Although larger validation studies are still necessary, preliminary results suggest mpMRI has a role in selecting patients for active surveillance. Less certain is the role of mpMRI in monitoring patients on active surveillance, as data on this will take a long time to mature. The biggest obstacles to routine use of prostate MRI are quality control, cost, reproducibility, and access. Nevertheless, there is great a potential for mpMRI to improve outcomes and quality of treatment. The major roles of MRI will continue to expand and its emerging use in standard of care approaches becomes more clearly defined and supported by increasing levels of data.

Keywords: Prostate cancer; active surveillance PI-RADS.; imaging; multiparametric magnetic resonance imaging; oncology; prostate specific antigen.

FIG. 1.. Fourty six-year old man with a serum PSA= 6.79 ng/mL with Gleason 3+3 prostate cancer diagnosis. Baseline mpMRI consisted of T2W MRI (a) ADC map (b) b1500 DW MRI (c) shows no lesion at the level of right apical portion of the prostate. Two year follow up axial T2W MRI (d) shows a lesion in the right apical peripheral zone, which is also positive on ADC map (e) and b1500 DW MRI (f) (serum PSA at 2 year follow up= 9.25 ng/mL). TRUS/MRI fusion biopsy revealed Gleason 4+3 with this lesion and patient became a radical prostatectomy candidate.

FIG. 2.. Sixty-year old man with a serum PSA= 4.58 ng/mL. Baseline mpMRI consisted of T2W MRI (a) ADC map (b) b1500 DW MRI (c) shows a focal lesion in the left mid peripheral zone. TRUS/MRI fusion guided biopsy revealed Gleason 3+3 prostate cancer within the lesion. One year follow up axial T2W MRI (d) ADC map (e) and b1500 DW MRI (f) shows no significant change within the lesion (serum PSA at 1 year follow up= 5.10 ng/mL). TRUS/MRI fusion biopsy revealed Gleason 3+3 with this lesion and patient continues to remain on active surveillance.