Volumetry of the Dominant Intraprostatic Tumour Lesion: Intersequence and Interobserver Differences on Multiparametric MRI.

To establish interobserver reproducibility of tumour volumetry on individual multiparametric(mp) prostate MRI sequences, validate measurements with histology and determine whether functional to morphological volume ratios reflect Gleason score.

Forty-one men with prostate cancer treated with prostatectomy (cohort 1) or radical radiotherapy (cohort 2) who had pre-treatment mp (T2-W, DW-, DCE-) MRI were studied retrospectively. Dominant intraprostatic lesions (DIPLs) were manually delineated on each sequence and volumes compared between observers (n=40 analysable) and with radical prostatectomy (n=20). Volume ratios of DW- and DCE- to T2-W MRI were documented and compared between Gleason grade 3+3, 3+4 and 4+3 or greater categories.

Limits of Agreement of DIPL volumes between observers were: T2-W 0.9, -1.1 cm(3), DW-MRI 1.3, -1.7 cm(3), DCE-MRI 0.74, -0.89 cm(3). In cohort 1, T2-W volumes overestimated fixed specimen histological volumes, (+33% observer 1, +16% observer 2); DW- and DCE-MRI underestimated histological volume, the latter markedly so (-32% observer 1, -79% observer 2). Differences between T2-W, DW- and DCE-MRI volumes were significant (p<10(-8)). The proportional volume of DW- (73.9+18.1 % observer 1, 72.5+21.9% observer 2) and DCE-MRI volume (42.6+24.6% observer 1, 34.3+24.9% observer 2) to T2-W volume was significantly different (p<10(-8)) but these volume ratios did not differ between Gleason grade.

The T2-W MRI DIPL volume variability between observers and with histology best reflects the GTV for radiotherapy planning. The volume of cellular tumour represented by DW-MRI is greater than the vascular (DCE) abnormality; ratios of both to T2-W volume are independent of Gleason score. Advances in knowledge: 1. Manual volume measurement of tumour is reproducible within 1cm(3) between observers on all sequences, confirming suitability across observers for radiotherapy planning. 2. Volumes derived on T2-W MRI most accurately represent in vivo lesion volumes. 3. The proportion of cellular (DW-) or vascular (DCE-) volume to morphological (T2-W) volume is not affected by Gleason score.

The British journal of radiology. 2017 Jan 05 [Epub ahead of print]

Hugh Harvey, Matthew R Orton, Veronica A Morgan, Chris Parker, David Dearnaley, Cyril Fisher, Nandita M deSouza

1 Cancer Research UK Imaging Centre at The Institute of Cancer Research, London and Royal Marsden NHS Foundation Trust, UK., 2 Academic Urology Unit at The Institute of Cancer Research, London and Royal Marsden NHS Foundation Trust, UK., 3 Department of Histopathology at The Institute of Cancer Research, London and Royal Marsden NHS Foundation Trust, UK.