1. Don Nguyen1, Sean Li1, Jinxing Yu, MD1
Multiparametric Prostate MRI in the Diagnosis of Locally Recurrent Prostate Cancer after Radiation Therapy: Correlation with MRI Guided Prostate Biopsy Findings
Don Nguyen1, Sean Li1, Jinxing Yu, MD1
1Virginia Commonwealth University
Introduction
Conclusion
Results
Prostate cancer is the most common malignant tumor in men and the second leading cause of cancer death in men [1]. When detected, radiation therapy, which includes external beam radiation or radioactive pellet brachytherapy, has been widely used as the definitive treatment for clinically localized prostate cancer [2]. Current imaging techniques for identifying local recurrence involve transrectal ultrasonography (TRUS) with random biopsy or conventional MRI; both contain considerable challenges [3]. TRUS with biopsy is poorly tolerated in an irradiated patient and risks errors from random sampling, often requiring repeated biopsies. In conventional MRI, tumor depiction in the irradiated prostate is limited by post-treatment changes [4-6].
However, recent advances in MR techniques have enabled improved detection of locally recurrent prostate cancer after radiation therapy. This improvement is mainly attributed to the addition of diffusion weighted imaging (DWI), dynamic contrast enhancement (DCE), and MR spectroscopy imaging (MRSI) to the prostate MR protocol [7,8]. Therefore, mp-MRI prostate examination uses T1- and T2-weighted imaging combined with one or more functional MR imaging (DWI/ADC, DCE and MRSI).
Certain limitations were imposed on our study. The main limitation was that there was no negative control group of prostate cancer patients without biochemical failure after radiation therapy. Second, our validation was performed against a biopsy reference standard rather than a prostatectomy reference standard, which introduces potential sampling error. However, the biopsy technique in all cases was performed using MRI guidance to sample suspicious lesions in peripheral zone, transitional zone, and/or seminal vesicle. Therefore, although our results lack prostatectomy correlation, they are likely correct. Third, this study had a small homogenous sample size; from our institution, 10 patients underwent MRI and MRGB of prostate after radiation treatment following rising PSA. Finally, the study was carried out retrospectively, which may contribute to confounding variables and selection biases. However, attempts to control confounding variables were implemented though multivariable analysis looking at different statistical outcome variables, such as sensitivity and specificity of each functional MR imaging, length of time between MRI and treatment, and final PSA level.
In summary, for the detection of locally recurrent prostate cancer in patients suspected of biochemical failure after radiation therapy, our results suggest that the use of multiparametric MRI showed a better diagnostic performance compared to conventional T2-weighted imaging alone.
Biopsy and histopathologic analysis of 10 patients treated with radiation therapy revealed 9 patients were positive for locally recurrent prostate cancer (Table 1). Retrospective analysis of mp-MRI exams confirmed conventional T2WI was not useful in differentiation of locally recurrent prostate cancer from benign lesions. Diffusion weighted imaging, dynamic contrast imaging enhancement, and MR spectroscopy were found to be significant in detecting the presence of focal recurrent prostate cancer (Table 2). Among them, DCE was instrumental in detecting the presence of locally recurrent prostate cancer in all positive cases (9 out of 9, 100%). DWI/ADC was found to be helpful in diagnosing 7 out of 9 positive cases (78%). MR spectroscopy, when available, was also useful serving as an adjunct with other functional MRI in detecting positive cases (4 out of 5, 80%). Following positive diagnosis of recurrent prostate cancer, 5 out of 9 patients underwent salvage therapy and PSA level was compared pre and postoperatively (Table 3).
Objectives
To retrospectively evaluate mp-MRI for depiction of local prostate cancer recurrence after radiation therapy using histopathologic findings as a standard of reference and to determine the sensitivity and specificity of mp-MRI for detecting local recurrence.
References
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Materials and Methods
Patient Population
This retrospective study included all patients who underwent mp-MRI and MRI-guided prostate biopsy, between January 2011 and May 2013, who had suspicion for clinical failure seen by slowly rising PSA after external beam radiation or radioactive pellet brachytherapy. 10 out of the 11 patients (mean age, 67.9 years; age range, years) were included in our retrospective analysis, of which 4 had received external beam radiation therapy and 6 received radioactive pellet therapy. An assessment was made on abnormal signal intensity on T2WI (Fig 1), diffusion restricted areas on diffusion weighted imaging (Fig 2), abnormal enhancement on dynamic contrast imaging enhancement (Fig 3), and elevated choline peaks on MR spectroscopy (Fig 4) for detecting local recurrence of prostate cancer. Results were correlated with MRI guided prostate biopsy pathology reports.
MR Imaging Technique
MR imaging was performed with a 1.5-T whole-body MR imager (Signa; GE Medical Systems, Milwaukee, Wis). Patients were examined in the supine position; the body coil was used for excitation, and the pelvic phased-array coil (GE Medical Systems) was used in combination with an expandable endorectal coil (Medrad, Pittsburgh, Pa) for signal reception.
Histology Reference Standard
Suspicious prostate lesion samples were obtained from MRI-guided biopsy for correlation with mp-MRI findings. Each sample was stained with H and E for clinical evaluation of the presence of tumor. Biopsy specimens were reviewed in consensus by 2 pathologists and the presence of recurrent tumor was recorded. The tumor volume percentage, Gleason score, and pathologic stage were determined for each sample. The magnitude of radiation-induced effects in benign gland and cancer was also assessed.
Acknowledgment
We are grateful to Dr. Ema Dragoescu for the pathologic evaluation of the prostate biopsies and to Dr. Anthony Trace for statistical advice.