MRI for Active Surveillance in Prostate Cancer: How I Do It

Active surveillance (AS) is an option for deferring or avoiding immediate treatment of low- to intermediate-risk prostate cancer by monitoring the disease to detect progression. Serial MRI enhances patient selection for AS and allows noninvasive monitoring of tumor progression. We have used MRI routinely at entry and during AS in a tertiary referral center for approximately 20 years. The Prostate Cancer Radiological Estimation of Change in Sequential Evaluation (PRECISE) scoring system aims to standardize MRI interpretation and reporting in patients with prostate cancer undergoing AS. It uses a 1-5 scale to convey radiologic change: regression (score of 1 or 2), stability (score of 3), or progression (score of 4 or 5). Although PRECISE recommendations encourage the measurement of visible lesions at each follow-up MRI examination, the consensus group did not establish an optimal way to measure changes in tumor size over time. Methods discussed in this article include using one- or two-axis measurements or estimating tumor volume with the ellipsoid formula or planimetry. We favor the routine measurement of tumor volume on each MRI scan in one sitting by one observer. We also discuss how to optimize intervals for MRI across different baseline risk categories, define the size change and MRI appearance that indicate clinically meaningful progression, and determine appropriate triggers for repeat biopsy and initiation of treatment.