Detection of the index tumour and tumour volume in prostate cancer using T 2‐weighted and diffusion‐weighted magnetic resonance imaging ( MRI ) alone

Objective To examine the performance of T 2‐weighted ( T2W ) and diffusion‐weighted ( DW ) magnetic resonance imaging ( MRI ) for detecting the index tumour in patients with prostate cancer and to examine the agreement between MRI and histology when assessing tumour volume ( TV ) and overall tumour burden. Patients and Methods The study included 199 consecutive patients with biopsy confirmed prostate cancer randomised to MRI before radical prostatectomy from D ecember 2009 to J uly 2012. MRI ‐detected tumours ( MRTs ) were ranked from 1 to 3 according to decreasing volume and were compared with histologically detected tumours ( HTs ) ranked from 1 to 3, with HT 1 = index tumour. Whole‐mount section histology was used as a reference standard. The TVs of true‐positive MRTs ( MRTVs 1–3) were compared with the TVs found by histology ( HTVs 1–3). All tumours were registered on a 30‐sector map and by classifying each sector as positive/negative, the rate of true‐positive and ‐negative sectors was calculated. Results The detection rate for the HT 1 (index tumour) was 92%; HT 2, 45%; and HT 3, 37%. The MRTV 1–3 vs the HTV 1–3 were 2.8 mL vs 4.0 mL (index tumour, P < 0.001), 1.0 mL vs 0.9 mL (tumour 2, P = 0.413), and 0.6 mL vs 0.5 mL (tumour 3, P = 0.492). The rate of true‐positive and ‐negative sectors was 50% and 88%, κ = 0.39. Conclusion A combination of T 2 W and DW MRI detects the index tumour in 92% of cases, although MRI underestimates both TV and tumour burden compared with histology.