Changes in apparent diffusion coefficient and T2 relaxation during radiotherapy for prostate cancer

Purpose: To evaluate regional and temporal changes in apparent diffusion coefficient (ADC) and T₂ relaxation during radiation therapy (RT) in patients with low and intermediate risk localized prostate cancer. Materials and Methods: Seventeen patients enrolled on a prospective clinical trial where MRI was acquired every 2 weeks throughout eight weeks of image-guided prostate IMRT (78 Gy/39 fractions). ADC and T₂ quantification used entire prostate, central gland, benign peripheral zone, and tumor-dense regions-of-interest, and mean values were evaluated for common response trends. Results: Overall, the RT responses were greater than volunteer measurement repeatability, and week 6 appeared to be an optimum time-point for early detection. RT effects on the entire prostate were best detected using ADC (5-7% by week 2, P < 0.0125), effects on peripheral zone were best detected using T₂ (19% reduction at week 6; P = 0.004) and effects on tumors were best detected using ADC (14% elevation at week 6; P = 0.004). Conclusion: ADC and T₂ may be candidate biomarkers of early response to RT warranting further investigation against clinical outcomes.