Evaluation of apparent diffusion coefficient and MR volumetry as independent associative factors for extra‐prostatic extension (EPE) in prostatic carcinoma

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Abstract
Background: To assess mean apparent diffusion coefficient (ADC) and MR‐derived tumor volume (Vt) as associative factors for extra‐prostatic extension (EPE) in prostate cancer (PCa).Methods: With institutional review board approval, 73 consecutive patients diagnosed with PCa at trans‐rectal ultrasound biopsy underwent preoperative multi‐parametric (T2W+DWI+DCE) 3 Tesla MRI before radical prostatectomy between 2012 and 2014; 52% (38/73) patients had EPE. Clinical parameters including: age, prostate serum antigen (PSA), digital rectal examination (DRE) and percentage positive cores (PPC) were recorded. Two blinded radiologists subjectively evaluated for EPE using PI‐RADS with T2W‐MRI. A third blinded radiologist recorded: mean ADC (mm2/s) of tumor and tumor volume on ADC and T2W (derived from planar volumetry). VtMAX (the largest volume on ADC or T2W) was documented. Multivariate and receiver operator characteristic analyses were performed.Results: There were no significant differences in age, DRE, or Gleason score between groups (P = 0.52, 0.06, 0.61, 0.36). PSA approached significance being higher with EPE (12.9 ± 12.6 versus 8.2 ± 7.4; P = 0.06). PPC was higher with EPE (60.9 ± 21.9% versus 38.3 ± 21.6%; P < 0.01) with an area under the curve (AUC) of 0.78 and sensitivity/specificity = 75.7/75% when PPC ≥ 45%. AUC for T2W‐MRI was 0.46–0.51 with sensitivity/specificity = 40.0–42.9/48.6–57.1% (R1, R2). Inter‐observer agreement was fair, k = 0.39. There was no difference in mean ADC between groups (0.89 ± 0.25 versus 0.88 ± 0.19 [EPE] mm2/s), P = 0.70. T2W‐Vt, ADC‐Vt, and VtMAX were larger with EPE (5.1 ± 7.4, 5.8 ± 6.5, 6.3 ± 7.4 cm3 versus 1.6 ± 1.8, 1.8 ± 1.3, 2.1 ± 1.8), P < 0.01. VtMAX AUC was 0.77 with sensitivity/specificity = 78.4/73.5% when VtMAX ≥ 2.1 cm3 which outperformed all other parameters (P > 0.05) except PPC (P = 0.6) for the diagnosis EPE.Conclusion: MR volumetry and percentage of positive core biopsies are associated with EPE; whereas, in this study, other clinical and MR parameters including mean ADC and subjective T2W‐MR analysis were not useful for assessment of EPE. J. MAGN. RESON. IMAGING 2016;43:726–736.

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