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      Volumetry of the dominant intraprostatic tumour lesion: intersequence and interobserver differences on multiparametric MRI

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          Abstract

          Objective:

          To establish the 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.

          Methods:

          41 males with prostate cancer treated with prostatectomy (Cohort 1) or radical radiotherapy (Cohort 2), who had pre-treatment mpMRI [ T 2 weighted (T2W) MRI, diffusion-weighted (DW)-MRI and dynamic contrast-enhanced (DCE)-MRI], were studied retrospectively. Dominant intraprostatic lesions (DIPLs) were manually delineated on each sequence and volumes were compared between observers ( n = 40 analyzable) and with radical prostatectomy ( n = 20). Volume ratios of DW-MRI and DCE-MRI to T2W MRI were documented and compared between Gleason grade 3 + 3, 3 + 4 and 4 + 3 or greater categories.

          Results:

          Limits of agreement of DIPL volumes between observers were: T2W MRI 0.9, −1.1 cm 3, DW-MRI 1.3, −1.7 cm 3 and DCE-MRI 0.74, −0.89 cm 3. In Cohort 1, T2W 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 T2W, DW- and DCE-MRI volumes were significant ( p < 10 −8). The ratio of DW-MRI volume (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 T2W volume was significantly different ( p < 10 −8), but these volume ratios did not differ between the Gleason grades.

          Conclusion:

          The low variability of the DIPL volume on T2W MRI between Observers and agreement with histology indicates its suitability for delineation of gross tumour volume for radiotherapy planning. The volume of cellular tumour represented by DW-MRI is greater than the vascular (DCE) abnormality; ratios of both to T2W volume are independent of Gleason score.

          Advances in knowledge:

          (1) Manual volume measurement of tumour is reproducible within 1 cm 3 between observers on all sequences, confirming suitability across observers for radiotherapy planning. (2) Volumes derived on T2W MRI most accurately represent in vivo lesion volumes. (3) The proportion of cellular (DW-MRI) or vascular (DCE-MRI) volume to morphological (T2W MRI) volume is not affected by Gleason score.

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          Most cited references26

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          Combined T2-weighted and diffusion-weighted MRI for localization of prostate cancer.

          The objective of our study was to compare T2-weighted MRI alone and T2 combined with diffusion-weighted imaging (DWI) for the localization of prostate cancer. T2-weighted imaging and DWI (b value = 600 s/mm2) were performed in 49 patients before radical prostatectomy using an endorectal coil at 1.5 T in this prospective trial. The peripheral zone of the prostate was divided into sextants and the transition zone into left and right halves. T2 images alone and then T2 images combined with apparent diffusion coefficient (ADC) maps (T2 + DWI) were scored for the likelihood of tumor and were compared with whole-mount histology results. Fixed window and level settings were used to display the ADC maps. Only tumors with an area of more than 0.13 cm2 (> 4 mm diameter) and a Gleason score of > or = 6 were considered significant. The area under the receiver operating characteristic curve (A(z)) was used to assess accuracy. In the peripheral zone, the A(z) value was significantly higher (p = 0.004) for T2 plus DWI (A(z) = 0.89) than for T2 imaging alone (A(z) = 0.81). Performance was poorer in the transition zone for both T2 plus DWI (A(z) = 0.78) and T2 (A(z) = 0.79). For the whole prostate, sensitivity was significantly higher (p or = 6 and diameter > 4 mm) within the peripheral zone of the prostate.
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            Definition of the prostate in CT and MRI: a multi-observer study.

            To determine, in three-dimensions, the difference between prostate delineation in magnetic resonance (MR) and computer tomography (CT) images for radiotherapy treatment planning. Three radiation oncologists, considered experts in the field, outlined the prostate without seminal vesicles both on CT, and axial, coronal, and sagittal MR images for 18 patients. To compare the resulting delineated prostates, the CT and MR scans were matched in three-dimensions using chamfer matching on bony structures. The volumes were measured and the interscan and interobserver variation was determined. The spatial difference between delineation in CT and MR (interscan variation) as well as the interobserver variation were quantified and mapped three-dimensionally (3D) using polar coordinates. A urethrogram was performed and the location of the tip of the dye column was compared with the apex delineated in CT and MR images. Interscan variation: CT volumes were larger than the axial MR volumes in 52 of 54 delineations. The average ratio between the CT and MR volumes was 1.4 (standard error of mean, SE: 0.04) which was significantly different from 1 (p < 0.005). Only small differences were observed between the volumes outlined in the various MR scans, although the coronal MR volumes were smallest. The CT derived prostate was 8 mm (standard deviation, SD: 6 mm) larger at the base of the seminal vesicles and 6 mm (SD 4 mm) larger at the apex of the prostate than the axial MRI. Similar figures were obtained for the CT and the other MRI scans. Interobserver variation: The average ratio between the volume derived by one observer for a particular scan and patient and the average volume was 0.95, 0.97, and 1.08 (SE 0.01) for the three observers, respectively. The 3D pattern of the overall observer variation (1 SD) for CT and axial MRI was similar and equal to 3.5 to 2.8 mm at the base of the seminal vesicles and 3 mm at the apex. CT-derived prostate volumes are larger than MR derived volumes, especially toward the seminal vesicles and the apex of the prostate. This interscan variation was found to be larger than the interobserver variation. Using MRI for delineation of the prostate reduces the amount of irradiated rectal wall, and could reduce rectal and urological complications.
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              Interobserver reproducibility of Gleason grading of prostatic carcinoma: general pathologist.

              Only a few large studies of interobserver reproducibility of Gleason grading of prostatic carcinoma exist. Thirty-eight biopsies containing prostate cancer were distributed for Gleason grading to 41 general pathologists in Georgia. These cases had "consensus" Gleason grade groups (2-4, 5-6, 7, and 8-10) that were agreed on by at least 7 of 10 urologic pathologists. The overall kappa (kappa) coefficient for interobserver agreement for these 38 cases was 0.435, barely moderate agreement, with a kappa range from 0.00 to 0.88. There was consistent undergrading of Gleason scores 5-6 (47%), 7 (47%) and, to a lesser extent, 8-10 (25%). In cases with consensus primary patterns, there was consistent undergrading of patterns 2 (32%), 3 (39%), and 5 (30%). Pattern 2 was often (17%) mistaken for pattern 3. Pattern 4 was often undergraded (21%) and also mistaken for pattern 5 (17%). The most significant (P < .005) demographic factor associated with better interobserver agreement was having learned Gleason grading at a meeting or course. We believe that Gleason grading can be learned to a satisfactory level of interobserver reproducibility and have undertaken additional studies that support this belief.
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                Author and article information

                Contributors
                Journal
                Br J Radiol
                Br J Radiol
                bjr
                The British Journal of Radiology
                The British Institute of Radiology.
                0007-1285
                1748-880X
                March 2017
                24 February 2017
                March 2017
                : 90
                : 1071
                : 20160416
                Affiliations
                [ 1 ]Cancer Research UK Imaging Centre, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, UK
                [ 2 ]Academic Urology Unit, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, UK
                [ 3 ]Department of Histopathology, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, UK
                Author notes
                Address correspondence to: Prof Nandita M deSouza. E-mail: nandita.desouza@ 123456icr.ac.uk
                Article
                D16416
                10.1259/bjr.20160416
                5601508
                28055249
                8a3709e8-ec59-4785-aa10-e92a9fd9facc
                © 2017 The Authors. Published by the British Institute of Radiology

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 Unported License http://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted non-commercial reuse, provided the original author and source are credited.

                History
                : Received on May 12, 2016
                : Revised on November 10, 2016
                : Accepted on January 3, 2017
                Page count
                Figures: 3, Tables: 2, References: 34, Pages: 8
                Categories
                Full Paper
                Technical/Instrumental

                Radiology & Imaging
                Radiology & Imaging

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