Predictive Value of Quantitative ADC, SUVmax, and the SUVmax/ADC Ratio for Biological Behavior and Prognosis in...

Background/Objectives: To investigate the importance of ADC, SUVmax, and SUVmax/ADC values in the prognosis and biological behavior of prostate cancer. Methods: In this retrospective study, ADC measurements in diffusion MRI were made by two radiologists by correlating the lesions with the highest SUVmax value from Ga-68 PSMA PET/CT examinations of 81 patients with prostate cancer. The quantitative values were compared with histopathological grade, presence of perineural invasion, and lymph node and bone metastasis. Results: For D'Amico high-risk patients, a statistically significant difference among the ADC, SUVmax, and SUVmax/ADC measurements was reported (p < 0.001). Cut-off values were defined as 0.52 (×10^-3 mm²/s) for ADC, 9.73 for SUVmax, and 20.28 for the SUVmax/ADC ratio (AUC = 0.887, 0.747, 0.817, respectively) for the high-risk categories. The Youden indices were 0.643, 0.405, and 0.437, respectively. In logistic regression, the SUVmax/ADC ratio was a significant predictor of the high-risk group (AUC = 0.844, p = 0.002), demonstrating superior performance to a model with individual ADC and SUVmax values (AUC = 0.796, p = 0.006). For the advanced-grade group, the SUVmax and SUVmax/ADC ratios differed significantly (p < 0.001). The CAPRA score showed significant correlations with all imaging biomarkers: negatively with ADC (rho = -0.456, p < 0.001) and positively with SUVmax (rho = 0.359, p = 0.001) and the SUVmax/ADC ratio (rho = 0.441, p < 0.001). The presence of perineural invasion had no significant correlation with any of the variables (p > 0.05). The presence of bone metastases and PSA and free PSA levels differed significantly (p = 0.003, p = 0.001, respectively). In the presence of lymph node metastasis, SUVmax and SUVmax/ADC ratios were found to be significant (p = 0.019, p = 0.01, respectively). In the survival (OS) analysis, a low ADC value was found to be associated with shorter survival (median OS: 61 vs. 106 months). Conclusions: Among advanced-grade and high-risk prostate cancer patients, ADC, SUVmax, and SUVmax/ADC values can be employed as alternative prognostic factors for predicting the biological behavior of the disease.