Preoperative lymph node staging in patients with primary prostate cancer: Comparison and correlation of quantitative imaging parameters in diffusion-weighted imaging and 11C-choline PET/CT

Purpose: To compare the diagnostic performance of DWI and 11C-choline PET/CT in the assessment of preoperative lymph node status in patients with primary prostate cancer. Material and methods: Thirty-three patients underwent DWI and 11C-choline PET/CT prior to prostatectomy and extended pelvic lymph node dissection. Mean standardised uptake value (SUV _mean ) and mean apparent diffusion coefficient (ADC) of 76 identified lymph nodes (LN) were measured and correlated with histopathology. ADC values and SUVs were compared using linear regression analysis. Results: A significant difference between benign and malignant LN was observed for ADC values (1.17 vs. 0.96 × 10 ^-3 mm ² /s; P < 0.001) and SUV _mean (1.61 vs. 3.20; P < 0.001). ROC analysis revealed an optimal ADC threshold of 1.01 × 10 ^-3 mm ² /s for differentiating benign from malignant LN with corresponding sensitivity/specificity of 69.70 %/78.57 % and an area under the curve (AUC) of 0.785. The optimal threshold for SUV _mean was 2.5 with corresponding sensitivity/specificity of 69.72 %/90.48 % and with an AUC of 0.832. ADC values and SUV _mean showed a moderate significant inverse correlation (r = -0.63). Conclusion: Both modalities reveal similar moderate diagnostic performance for preoperative lymph node staging of prostate cancer, not justifying their application in routine clinical practice at this time. The only moderate inverse correlation between ADC values and SUV _mean suggests that both imaging parameters might provide complementary information on tumour biology. • Conventional imaging shows low performance for lymph node staging in prostate cancer. • DWI and 11C-choline PET/CT both provide additional functional information • Both functional modalities reveal only moderate diagnostic performance.