Whole-body magnetic resonance imaging (WB-MRI) reporting with the METastasis Reporting and Data System for Prostate Cancer (MET-RADS-P): inter-observer agreement between readers of different expertise levels

Abstract

Background: The METastasis Reporting and Data System for Prostate Cancer (MET-RADS-P) guidelines are designed to enable reproducible assessment in detecting and quantifying metastatic disease response using whole-body magnetic resonance imaging (WB-MRI) in patients with advanced prostate cancer (APC). The purpose of our study was to evaluate the inter-observer agreement of WB-MRI examination reports produced by readers of different expertise when using the MET-RADS-P guidelines.

Methods: Fifty consecutive paired WB-MRI examinations, performed from December 2016 to February 2018 on 31 patients, were retrospectively examined to compare reports by a Senior Radiologist (9 years of experience in WB-MRI) and Resident Radiologist (after a 6-months training) using MET-RADS-P guidelines, for detection and for primary/dominant and secondary response assessment categories (RAC) scores assigned to metastatic disease in 14 body regions. Inter-observer agreement regarding RAC score was evaluated for each region by using weighted-Cohen's Kappa statistics (K).

Results: The number of metastatic regions reported by the Senior Radiologist (249) and Resident Radiologist (251) was comparable. For the primary/dominant RAC pattern, the agreement between readers was excellent for the metastatic findings in cervical, dorsal, and lumbosacral spine, pelvis, limbs, lungs and other sites (K:0.81-1.0), substantial for thorax, retroperitoneal nodes, other nodes and liver (K:0.61-0.80), moderate for pelvic nodes (K:0.56), fair for primary soft tissue and not assessable for skull due to the absence of findings. For the secondary RAC pattern, agreement between readers was excellent for the metastatic findings in cervical spine (K:0.93) and retroperitoneal nodes (K:0.89), substantial for those in dorsal spine, pelvis, thorax, limbs and pelvic nodes (K:0.61-0.80), and moderate for lumbosacral spine (K:0.44).

Conclusions: We found inter-observer agreement between two readers of different expertise levels to be excellent in bone, but mixed in other body regions. Considering the importance of bone metastases in patients with APC, our results favor the use of MET-RADS-P in response to the growing clinical need for monitoring of metastasis in these patients.

Keywords: Inter-observer agreement; MET-RADS-P; Prostate cancer; Whole body MRI.

Conflict of interest statement

PS is part owner of QMRI-Tech a company that provides support for medical physics activities and radiological research.

All other authors indicate that they have no competing interests.

Figures

Fig. 1

Example images of a 69-year-old man with castration resistant prostate cancer in progression, with primary/dominant RAC 5. a) and b) In the course of abiraterone treatment, axial diffusion-weighted (DW) b900 images (upper) and T1-weighted (T1) images (lower) show the appearance of a small acetabular lesion on the left. Inverted grayscale maximum intensity projection of the c) pre- and d) post-treatment b900 images, respectively illustrate the appearance of the left acetabular lesion (arrow) and an increase in size of an existing pelvic bone lesion (arrow head)

Fig. 2

Example images of a 76-year-old man with advanced prostate cancer that is not progressing, with primary/dominant RAC 3. a) Axial DW b900 images (upper) and T1 images (lower) show the presence of lesions in pelvic bone (arrows) that are unchanged in b) follow-up MRI. The c) initial and d) follow-up b900 maximum intensity projection images confirm stability of disease throughout the body

Fig. 3

Example images of a 67-year-old man with metastatic hormone sensitive prostate cancer showing response, with primary/dominant RAC 1. a) Axial ADC map (upper) and T1 images (lower) at the start of luteinizing hormone releasing hormone agonist therapy show presence of a dorsal (T8 level) spine lesion with ADC value = 784 μm2/sec. b) Despite the follow-up T1 image (lower image) showing an increase in the lesion size due to the presence of edema accompanied by an increase in the ADC value = 1608 μm2/sec of the T8 lesion (arrows), suggestive of highly likely response. Three-dimensional b900 maximum intensity projection images c) at start of therapy and d) at follow-up illustrate the disappearance of the T8 lesion

Fig. 4

Example images of a 76-year-old man with castration resistant prostate cancer in treatment with bicalutamide and leuprolide acetate where the observers differed in their response assessments of a T11 vertebral body metastasis. The original lesion is seen in a) axial DW b900 images (upper) and T1 images (lower) and corresponding c) inverted grayscale maximum intensity projections. At a distance of 2 months b) and d), the Resident Radiologist assigned it as stable (RAC 3) whereas the Senior Radiologist considered it likely to be in progression (RAC 4)

Fig. 5

Impact of WB-MRI treatment monitoring on patient management in our 31 patient cohort. Response assessment categories indicating disease that is likely or highly likely to be progressing (RAC > 3) reported by the Senior Radiologist (SR) led to therapy changes for 15 patients, and the addition of radiotherapy in 6 patients. The overall agreement between the Resident Radiologist (RR) and the SR regarding management was 96.7% with a Cohen’s κ of 0.92 (almost perfect agreement) differing only in one case where the Resident Radiologist (RR) assigned a RAC > 3 and the SR had assigned a RAC ≤ 3 (stable disease, or disease likely or highly likely to be responding)