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

BJR Received: 12 May 2016 https://doi.org/10.1259/bjr.20160416 Revised: 10 November 2016 Accepted: 3 January 2017 © 2017 The Authors. Published by the British Institute of Radiology 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. Cite this article as: Harvey H, Orton MR, Morgan VA, Parker C, Dearnaley D, Fisher C, et al. Volumetry of the dominant intraprostatic tumour lesion: intersequence and interobserver differences on multiparametric MRI. Br J Radiol 2017; 90: 20160416. FULL PAPER Volumetry of the dominant intraprostatic tumour lesion: intersequence and interobserver differences on multiparametric MRI 1 HUGH HARVEY, FRCR, 1MATTHEW R ORTON, PhD, 1VERONICA A MORGAN, MSc, 2CHRIS PARKER, FRCR, DAVID DEARNALEY, FRCR, 3CYRIL FISHER and 1NANDITA M DESOUZA, FRCR 2 1 Cancer Research UK Imaging Centre, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, UK 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 2 Address correspondence to: Prof Nandita M deSouza E-mail: 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 [T2 weighted (T2W) MRI, diffusion-weighted (DW)-MRI and dynamic contrastenhanced (DCE)-MRI], were studied retrospectively. Dominant intraprostatic lesions (DIPLs) were manually delineated on each sequence and volumes were compared between observers (n 5 40 analyzable) and with radical prostatectomy (n 5 20). Volume ratios of DW-MRI and DCE-MRI to T2W MRI were documented and compared between Gleason grade 3 1 3, 3 1 4 and 4 1 3 or greater categories. Results: Limits of agreement of DIPL volumes between observers were: T2W MRI 0.9, 21.1 cm3, DW-MRI 1.3, 21.7 cm3 and DCE-MRI 0.74, 20.89 cm3. In Cohort 1, T2W volumes overestimated fixed specimen histological volumes (133% Observer 1, 116% Observer 2); DW- and DCE-MRI underestimated histological volume, the latter markedly so (232% Observer 1, 279% Observer 2). Differences between T2W, DW- and DCE-MRI volumes were significant (p , 1028). The ratio of DW-MRI volume (73.9 6 18.1% Observer 1, 72.5 6 21.9% Observer 2) and DCE-MRI volume (42.6 6 24.6% Observer 1, 34.3 6 24.9% Observer 2) to T2W volume was significantly different (p , 1028), 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 cm3 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. INTRODUCTION The soft-tissue contrast on T2 weighted (T2W) MRI is preferred over X-ray CT for prostate tumour identification, staging1–4 and defining the dominant intraprostatic lesion (DIPL).5 Furthermore, additional information available from diffusion-weighted (DW)MRI and dynamic contrast enhanced (DCE)-MRI techniques, collectively termed multiparametric (mp)MRI, may be exploited to improve sensitivity and specificity for tumour identification over T2W imaging alone.6 An accurate definition of gross tumour volume (GTV) derived from these images is essential in planning radiation therapy,7 particularly when giving boost doses to the DIPL:8 overestimation of the GTV increases the risk of radiation-induced complications to organs at risk such as the rectal wall, and underestimation reduces the long-term efficacy of treatment.9 However, as there is increasing evidence that the volumes defined on individual mpMRI sequences are significantly different from each other10 and depend on underlying histology,11,12 the optimal sequence on which to outline the GTV remains to be established. BJR Harvey et al Traditionally, tumour outlines are carried out on T2W images for radiation therapy planning. Although this involves simultaneous viewing of all mpMR images,13 the specific and independent influence of the DW-MRI- and DCE-MRI-identified tumour on the morphological (T2W) outlines, which may vary with Gleason grade, has not been documented. A recent large study showed that the maximum volume measured on mpMRI correlated best with histology.14 The purpose of this study therefore was to establish the interobserver reproducibility of prostate tumour volumetry on individual sequences obtained from mpMRI, validate the measurements against histology and determine whether the proportion of cellular (DW-MRI) or vascular (DCE-MRI) volume to morphological (T2W MRI) volume reflects the Gleason score. METHODS AND MATERIALS Patients Imaging data were obtained from 41 males with prostate cancer (mean age 66.7 6 7.6 years, prostate-specific antigen range 3.0–32.0 ng ml21, clinical grade T1–T3, Gleason grade 6–8) who had been enrolled consecutively in 2 unrelated prospective studies approved by the local institutional review board and had given written consent for use of their data. Acquired images were therefore analyzed retrospectively. All patients had mpMRI with positive histology on a standardized 8–10 core randomly sampled transrectal ultrasound-guided biopsy performed between 4 and 12 weeks previously (median 85 days, range 8–231 days). All patients were treatment naı̈ve at the time of scanning. The first 20 patients (Cohort 1) were treated with radical prostatectomy and the latter 21 patients (Cohort 2) underwent radiation therapy with dose boosting to the DIPL. In Cohort 1, mpMRI was performed a mean of 16.7 days (median 12 days, range 1–54 days) prior to prostatectomy. In Cohort 1, 3 patients were Gleason grade 3 1 3, 12 patients were 3 1 4 and 5 patients were 4 1 3 or greater. In Cohort 2, 5 patients were Gleason grade 3 1 3, 10 patients were 3 1 4 and 6 patients were 4 1 3 or greater. Image acquisition All imaging was performed with an endorectal coil. Cohort 1 was studied at 1.5 T and 55 ml of room air was used for inflation of the balloon. Cohort 2 w (...truncated)