Magnetic resonance imaging has become a central component of monitoring patients undergoing active surveillance for prostate cancer. Evidence suggests it is likely more accurate than prostate-specific antigen testing or biopsy for assessing structural change in small, visible tumors and can detect most higher-grade disease. Used serially, it may function as a longitudinal safety net.

The practical implication is that magnetic resonance imaging reporting should emphasize change over time rather than a single time point, while still being interpreted alongside clinical factors such as prostate-specific antigen levels and patient characteristics.

Moving Beyond Diameter to Volume Assessment

A key shift described by the researchers is moving beyond reliance on maximum diameter alone:

• Lesions with the same maximum diameter may differ substantially in volume

• Volume may better reflect tumor burden

• The rate of change over time may be more clinically relevant than absolute size

Routine volume estimation—using planimetry or ellipsoid calculations—can support longitudinal assessment. The researchers emphasized that consistency in measurement technique is more important than absolute precision.

PRECISE Provides Structure but Has Limitations

The Prostate Cancer Radiological Estimation of Change in Sequential Evaluation (PRECISE) system offers a standardized framework for reporting change:

• Scores from 1 to 5 reflect regression through progression

• The system supports communication and follow-up planning

However, the researchers noted that PRECISE does not quantify the magnitude or rate of change. They suggested that combining PRECISE scoring with quantitative measures such as tumor volume may improve clinical interpretation.

A Practical Approach to Reporting

The researchers described an approach used in their practice to improve longitudinal assessment:

• Review all prior magnetic resonance imaging studies together, ideally by the same reader

• Measure lesion volume consistently at each time point

• Generate a longitudinal series of volume estimates

Reports may include:

• Absolute volume change

• Estimated growth rate or volume doubling time

• Changes in lesion conspicuity, including diffusion-weighted imaging characteristics

This approach may add limited time to reporting while providing more clinically useful information.

Findings That May Warrant Closer Evaluation

The researchers emphasized focusing on measurable and reproducible changes over time rather than isolated findings.

Potential indicators of progression include:

• An increase in tumor volume beyond expected measurement variability

• A faster rate of growth, such as a shorter volume doubling time

• Changes in lesion conspicuity on magnetic resonance imaging

• Changes in apparent diffusion coefficient values, which have been associated with tumor enlargement and possible upgrading in smaller studies

They also noted that imaging findings should be considered alongside prostate-specific antigen trends, patient age, comorbidities, and prior histologic findings when determining the need for repeat biopsy or treatment.

Practical Reporting Considerations

• Include longitudinal context: Compare findings with baseline and prior studies

• Combine qualitative and quantitative data: Use PRECISE scoring alongside volume and growth estimates

• Emphasize consistency: Use the same measurement approach across time points

Bottom Line

Magnetic resonance imaging plays an important role in active surveillance for prostate cancer. Its value may be greatest when used to assess change over time—particularly through volume estimation and growth rate—while being integrated with clinical and laboratory data rather than used in isolation.

Disclosures: The researchers reported no funding. Conflicts of interest were disclosed in supplementary materials.

Source: Radiology