The Utility of Mean Apparent Diffusion Coefficient Value in Patients with Prostate Cancer Treated with Definitive Radiotherapy

Abstract

<h3>Purpose/Objective(s)</h3> By providing more objective measurements, quantitative magnetic resonance imaging (MRI) has the potential to further improve prediction of treatment outcomes for prostate cancer patients. The purpose of this study was to determine whether quantitative multiparametric MRI performed prior to treatment can accurately predict the biochemical outcome of prostate cancer patients receiving definitive radiotherapy (RT). <h3>Materials/Methods</h3> The clinical data of 503 prostate cancer patients who received definitive radiation therapy (RT) between June 2008 and September 2021 were analyzed retrospectively. Prior to RT, all patients had a prostate multiparametric MRI on a 3T MRI scanner. A radiologist outlined the index lesion and measured the quantitative apparent diffusion coefficient (ADC). The Phoenix criteria were used to define biochemical failure. The primary endpoints were failure from biochemical failure (FFBF) and progression free survival (PFS). <h3>Results</h3> The median age of the population was 69 years (range: 47–87 years). According to D'Amico risk categories, there were 183 patients (36.4%) classified as low risk, 156 patients (31%) classified as intermediate risk, and 164 patients (32.6%) classified as high risk. The mean ADC values for tumor and normal prostate tissue were 0.712±0.158 µm²/ms and 1.365±0.227 µm²/ms, respectively (p<0.001). The ADC values were significantly lower in patients with higher PSA (≥20 ng/mL), advanced T stage (≥T3a), nodal metastasis, higher ISUP score (≥3) and high-risk group compared to their counterparts. The median duration of follow-up was 72.9 months (range, 4.3–170.6 months) for the entire cohort. The 5-year FFBF and PFS rates were 93.2% and 86.2%, respectively. Biochemical failure was observed in 42 patients (9.3%). After ‘Receiver Operating Characteristics' (ROC) curve analysis, the cut-off point of ADC for predicting high-risk progression was 0.653 µm²/ms with area under curve of 0.656 (95%CI 0.581 – 0.736; p<0.001). In univariate analysis, PSA, T stage, ISUP score, risk group were significant prognostic factors for FFBF and PFS. Additional prognostic factor for OS was N stage, and age was for PFS. The 5-year FFBF for lower and higher ADC values were 89.1% and 95.6%, respectively (p<0.001). The 5-year PFS was significantly less for patients with lower ADC compared to those with higher ADC (82.2% vs. 88.5%; p = 0.002). In multivariate analysis higher ISUP score and lower ADC values were independent predictors for worse FFBF and PFS rates. Additional predictive factor for dismal PFS was older age. <h3>Conclusion</h3> Our findings suggest that quantitative ADC values of the index lesion may be used to predict biochemical failure and disease progression in patients with prostate cancer following definitive RT. Inferior biochemical control was associated with lower ADC values and higher ISUP scores.