Objectives: To assess the accuracy and interobserver variability of T2-weighted (T2W) and contrast-enhanced dynamic (CE-Dyn) magnetic resonance imaging (MRI) in predicting the results of transrectal biopsy in patients with suspected recurrent prostate cancer after external beam radiotherapy.
Methods: A total of 22 patients with increasing prostate-specific antigen levels after external beam radiotherapy for prostate cancer underwent T2W and CE-Dyn MRI of the prostate. The CE-Dyn sequence (acquisition time 30 seconds) was repeated three times after the injection of gadolinium. All patients underwent subsequent transrectal biopsy. Three independent readers interpreted the MRI scans. The MRI and biopsy results were correlated in 10 prostate sectors (the sextants of the peripheral zone, the two transitional zones, and the two seminal vesicles).
Results: Biopsy cores were obtained in 147 prostate sectors. Of these, 63 were positive for cancer in 19 patients. On the T2W images, the three readers interpreted as positive for cancer 15, 15, and 13 of the 19 patients showing cancer at biopsy. They interpreted as negative 3, 0, and 1 of the 3 patients showing no cancer at biopsy. On CE-Dyn images, the three readers correctly classified all the patients as positive or negative for cancer. The T2W and CE-Dyn MRI findings were concordant with biopsy results in, respectively, 81 to 95 and 107 to 117 prostate sectors (P <0.001 and P <0.01 for readers 1 and 2 and was nonsignificant for reader 3). The interobserver agreement was better for CE-Dyn images (kappa = 0.63 to 0.70) than for the T2W images (kappa = 0.18 to 0.39). The MRI-calculated tumor volumes and the mean biopsy core invasion rates were significantly correlated on the CE-Dyn images for all readers. They correlated significantly on T2W images only for one reader.
Conclusions: CE-Dyn MRI depicts the intraprostatic distribution of recurrent cancer after external beam radiotherapy more accurately and with less interobserver variability than T2W MRI.