[Active surveillance for prostate cancer: usefulness of endorectal MR at 1.5 Tesla with pelvic phased array coil in detecting significant tumors]

[Preoperative endorectal MRI in prostate cancer: a monocentric retrospective cohort]

INTRODUCTION

The aim of the study was to assess the added value of a prostatic MRI performed in a non-expert center before radical prostatectomy for prostate cancer.

PATIENTS AND METHODS

All patients considered for a radical prostatectomy for a clinically localised prostate cancer in our institution between June 2006 and April 2011 were analysed. They underwent a systematic endorectal 1.5 T MRI [eMRI] (T2 and diffusion-weighted imaging). The procedure was performed at least 8 weeks after transrectal ultrasound guided prostate biopsies. They were analyzed by a single experimented genitourinary radiologist. The preoperative characteristics and biopsy data were collected, as the eMRI interpretation using a systematic scale. Correlation between eMRI and final histopathology has been analyzed (standardized pathological report using the Stanford procedure). We considered the following points: extracapsular extension, seminal vesicle invasion and cancer localisation. Cancer localization was analyzed both by halves (left/right) and on sextant-basis (base, middle, apex, left and right respectively). For each data, sensitivity, specificity, positive (PPV) and negative predictive value (NPV) were calculated. Finally, we compared the results with those from the Partin's table and the Kattan's nomogram for T stage.

RESULTS

Two hundred and fifteen patients underwent a radical prostatectomy, having a mean age of 63 ± 6 years, a mean PSA: 7.8 ± 3.8 ng/mL. One hundred and fifty-nine patients had organ confined disease. Fifty-six had pT3 disease (50 pT3a and 6 pT3b). Sensibilities and specificities were the following: for extracapsular extension 26% and 96%; for seminal vesicle invasion 17% and 98%; for cancer localisation 64% and 74%; for prediction of left or right side 81% and 48%.

DISCUSSION

MRI showed equal performances compared to the Partin's table and the Kattan's nomogram for T stage. It showed lower performance compared to biopsy results for cancer localization (sensitivity 88%, specificity 70%). Literature provides wide ranges of results for eMRI. The results of this study were at the low limit of these ranges but reflect everyday practice. When performed, as it was in our study, eMRI did not seem to be accurate for staging. It had at best a very limited added value compared to the existing tools.

Correlation of magnetic resonance imaging tumor volume with histopathology

PURPOSE

The biology of prostate cancer may be influenced by the index lesion. The definition of index lesion volume is important for appropriate decision making, especially for image guided focal treatment. We determined the accuracy of magnetic resonance imaging for determining index tumor volume compared with volumes derived from histopathology.

MATERIALS AND METHODS

We evaluated 135 patients (mean age 59.3 years) with a mean prostate specific antigen of 6.74 ng/dl who underwent multiparametric 3T endorectal coil magnetic resonance imaging of the prostate and subsequent radical prostatectomy. Index tumor volume was determined prospectively and independently by magnetic resonance imaging and histopathology. The ellipsoid formula was applied to determine histopathology tumor volume, whereas manual tumor segmentation was used to determine magnetic resonance tumor volume. Histopathology tumor volume was correlated with age and prostate specific antigen whereas magnetic resonance tumor volume involved Pearson correlation and linear regression methods. In addition, the predictive power of magnetic resonance tumor volume, prostate specific antigen and age for estimating histopathology tumor volume (greater than 0.5 cm(3)) was assessed by ROC analysis. The same analysis was also conducted for the 1.15 shrinkage factor corrected histopathology data set.

RESULTS

There was a positive correlation between histopathology tumor volume and magnetic resonance tumor volume (Pearson coefficient 0.633, p <0.0001), but a weak correlation between prostate specific antigen and histopathology tumor volume (Pearson coefficient 0.237, p = 0.003). On linear regression analysis histopathology tumor volume and magnetic resonance tumor volume were correlated (r(2) = 0.401, p <0.00001). On ROC analysis AUC values for magnetic resonance tumor volume, prostate specific antigen and age in estimating tumors larger than 0.5 cm(3) at histopathology were 0.949 (p <0.0000001), 0.685 (p = 0.001) and 0.627 (p = 0.02), respectively. Similar results were found in the analysis with shrinkage factor corrected tumor volumes at histopathology.

CONCLUSIONS

Magnetic resonance imaging can accurately estimate index tumor volume as determined by histology. Magnetic resonance imaging has better accuracy in predicting histopathology tumor volume in tumors larger than 0.5 cm(3) than prostate specific antigen and age. Index tumor volume as determined by magnetic resonance imaging may be helpful in planning treatment, specifically in identifying tumor margins for image guided focal therapy and possibly selecting better active surveillance candidates.