Multiparametric MRI-based intra prostatic tumor volume delineation in localized prostate cancer

Background: Multiparametric MR imaging (mpMRI) has shown promising results in the diagnosis and localization of prostate cancer. Furthermore, mpMRI may play an important role in identifying a suitable target volume for intraprostatic radiotherapy boost. We sought to investigate the level of correlation between dominant tumor foci contoured on various mpMRI sequences. Methods: mpMRI data from 18 patients with MR-guided biopsy-proven prostate cancer were obtained from the SPIE-AAPM-NCI Prostate MR Classification Challenge. Each case consisted of T2-weighted, apparent diffusion coefficient (ADC), and ktrans images computed from dynamic contrast-enhanced sequences. All image sets were rigidly co-registered, and the dominant tumor foci were identified and contoured for each MRI sequence. Hausdorff distance (HD), mean distance to agreement (MDA), and Dice and Jaccard coefficients were calculated between the contours for each pair of MRI sequences (i.e., T2 vs. ADC, T2 vs. ktrans, and ADC vs. ktrans). The Pearson correlation coefficient (PCC) was also obtained for Dice and Jaccard between these image pairs. Results: The dominant tumor foci were located in the peripheral zone, transition zone, and anterior fibromuscular stroma in 5 (28%), 7 (39%), and 6 (33%) patients, respectively. Mean tumor volumes in the T2-weighted, ADC, and ktrans sequences were 2.71 +/-2.74 mL, 2.71 +/-2.67 mL, and 2.21 +/-1.86 mL, respectively. Mean HD and MDA were lowest (4.34 +/-1.52 mm and 1.00 +/-0.52 mm) and Dice and Jaccard coefficients highest (0.74 +/-0.12 and 0.60 +/-0.15) for T2 vs. ADC. The PCC for Dice was 0.15 between T2 vs. ADC and T2 vs. ktrans, 0.37 between T2 vs. ADC and ADC vs. ktrans, and 0.62 between T2 vs. ktrans and ADC vs. ktrans, and similar values were obtained for Jaccard (0.12, 0.32, and 0.67, respectively). Four patients were excluded in the PCC calculation as no vascular permeability was visible in the ktrans maps. Conclusions: This analysis suggests that T2-weighted and ADC sequences have high correlation in identifying a suitable intraprostatic radiotherapy boost volume for localized prostate cancer. Furthermore, ktrans maps may provide additional information for tumor volume delineation