Diffusion-weighted magnetic resonance imaging for monitoring prostate cancer progression in patients managed by active surveillance.

Objectives: We studied patients managed by active surveillance to determine whether there was a difference over time in apparent diffusion coefficients (ADCs) derived from diffusion-weighted MRI in those who progressed to radical treatment (progressors, n = 17) compared with those who did not (non-progressors, n = 33).

Methods: 50 consecutive patients (Stage T1/2a, Gleason grade ≤ 3+4, prostate-specific antigen (PSA) <15 ng ml⁻¹, <50% cores positive) were imaged endorectally (baseline and 1-3 years follow-up) with T₂ weighted (T₂W) and echo-planar diffusion-weighted MRI sequences. Regions of interest drawn on ADC maps with reference to the T₂W images yielded ADC(all) (b = 0-800), ADC(fast) (b = 0-300) and ADC(slow) (b = 300-800) for whole prostate (minus tumour) and tumour (low signal-intensity peripheral zone lesion in biopsy-positive octant).

Results: Tumour and whole prostate ADC(all) and ADC(fast) were significantly reduced over time in progressors (p = 0.03 and 0.03 for tumours, respectively; p = 0.02 and 0.007 for the whole prostate, respectively). There were no significant changes in ADC over time in non-progressors. A 10% reduction in tumour ADC(all) indicated progression with a 93% sensitivity and 40% specificity (A(z) of receiver operating characteristic (ROC) curve = 0.68). Percentage reductions in whole prostate ADC(all), ADC(fast) and ADC(slow) were also significantly greater in progressors than in non-progressors (p = 0.01, 0.03 and 0.008, respectively).

Conclusion: This pilot study shows that DW-MRI has potential for monitoring patients with early prostate cancer who opt for active surveillance.