Quantitative 3T multiparametric MRI of benign and malignant prostatic tissue in patients with and without local recurrent prostate cancer after external-beam radiation therapy

Abstract

Background: Post-radiotherapy locally recurrent prostate cancer (PCa) patients are candidates for focal salvage treatment. Multiparametric MRI (mp-MRI) is attractive for tumor localization. However, radiotherapy-induced tissue changes complicate image interpretation. To develop focal salvage strategies, accurate tumor localization and distinction from benign tissue is necessary.

Purpose: To quantitatively characterize radio-recurrent tumor and benign radiation-induced changes using mp-MRI, and investigate which sequences optimize the distinction between tumor and benign surroundings.

Study type: Prospective case-control.

Subjects: Thirty-three patients with biochemical failure after external-beam radiotherapy (cases), 35 patients without post-radiotherapy recurrent disease (controls), and 13 patients with primary PCa (untreated).

Field strength/sequences: 3T; quantitative mp-MRI: T₂ -mapping, ADC, and K^trans and k_ep maps.

Assessment: Quantitative image-analysis of prostatic regions, within and between cases, controls, and untreated patients.

Statistical tests: Within-groups: nonparametric Friedman analysis of variance with post-hoc Wilcoxon signed-rank tests; between-groups: Mann-Whitney tests. All with Bonferroni corrections. Generalized linear mixed modeling to ascertain the contribution of each map and location to tumor likelihood.

Results: Benign imaging values were comparable between cases and controls (P = 0.15 for ADC in the central gland up to 0.91 for k_ep in the peripheral zone), both with similarly high peri-urethral K^trans and k_ep values (min^-1 ) (median [range]: K^trans = 0.22 [0.14-0.43] and 0.22 [0.14-0.36], P = 0.60, k_ep = 0.43 [0.24-0.57] and 0.48 [0.32-0.67], P = 0.05). After radiotherapy, benign central gland values were significantly decreased for all maps (P ≤ 0.001) as well as T₂ , K^trans , and k_ep of benign peripheral zone (all with P ≤ 0.002). All imaging maps distinguished recurrent tumor from benign peripheral zone, but only ADC, K^trans , and k_ep were able to distinguish it from benign central gland. Recurrent tumor and peri-urethral K^trans values were not significantly different (P = 0.81), but k_ep values were (P < 0.001). Combining all quantitative maps and voxel location resulted in an optimal distinction between tumor and benign voxels.

Data conclusion: Mp-MRI can distinguish recurrent tumor from benign tissue.

Level of evidence: 2 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:269-278.