Prostate tumour volumes: evaluation of the agreement between magnetic resonance imaging and histology using novel co‐registration software

Abstract

Objective To evaluate the agreement between prostate tumour volume determined using multiparametric magnetic resonance imaging (MRI) and that determined by histological assessment, using detailed software-assisted co-registration. Materials and Methods A total of 37 patients who underwent 3T multiparametric MRI (T2-weighted imaging [T2WI], diffusion-weighted imaging [DWI]/apparent diffusion coefficient [ADC], dynamic contrast-enhanced [DCE] imaging) were included. A radiologist traced the borders of suspicious lesions on T2WI and ADC and assigned a suspicion score of between 2 and 5, while a uropathologist traced the borders of tumours on histopathological photographs. Software was used to co-register MRI and three-dimensional digital reconstructions of radical prostatectomy specimens and to compute imaging and histopathological volumes. Agreement in volumes between MRI and histology was assessed using Bland–Altman plots and stratified by tumour characteristics. Results Among 50 tumours, the mean differences (95% limits of agreement) in MRI relative to histology were −32% (−128 to +65%) on T2WI and −47% (−143 to +49%) on ADC. For all tumour subsets, volume underestimation was more marked on ADC maps (mean difference ranging from −57 to −16%) than on T2WI (mean difference ranging from −45 to +2%). The 95% limits of agreement were wide for all comparisons, with the lower 95% limit ranging between −77 and −143% across assessments. Volume underestimation was more marked for tumours with a Gleason score ≥7 or a MRI suspicion score 4 or 5. Conclusion Volume estimates of prostate cancer using MRI tended to substantially underestimate histopathological volumes, with a wide variability in extent of underestimation across cases. These findings have implications for efforts to use MRI to guide risk assessment.

Image Guided Focal Therapy for Magnetic Resonance Imaging Visible Prostate Cancer: Defining a 3-Dimensional Treatment Margin Based on Magnetic Resonance Imaging Histology Co-Registration Analysis

“…10–13 Using affine transformation and compensation for changes in volume and shape 14 we previously performed such an investigation with a validated, automated 3D co-registration system. 15 We observed consistent underestimation of tumor volume by MRI, indicating that actual tumor boundaries are expected to be located beyond the boundaries predicted by the visualized lesion on MRI. This difference in lesion boundaries has a critical impact in planning and performing focal therapy procedures, given that treatment of only the MRI visualized lesion leaves a portion of tumor untreated due to the larger histological volume.…”

Magnetic Resonance Imaging Underestimation of Prostate Cancer Geometry: Use of Patient Specific Molds to Correlate Images with Whole Mount Pathology

“…17,18 Their patients had a mean tumor volume of 1.38 cc compared to 2.5 cc in the current study. In addition, their work was restricted to a small number of men (33 and 37) who were retrospectively selected.…”

“…3) ROI contours were made on the T2-weighted image only but segmenting on multiple co-registered sequences may improve accuracy. 13,15,17 Incorporating additional sequences is complicated by geometric distortion and patient motion but advances in series registration may enable improvements in ROI delineation. 4) Interpretation of mpMRI and reporting guidelines have been tailored for suspicion grading and the guidance of targeted biopsy rather than for guiding targeted treatment.…”

“…More recent publications indicate the opposite, that is that actual tumor volume may be up to 150% of the MRI estimate. 14,17,18 Due to variations in imaging technology, contouring procedure and data analysis, available volume correlation studies have yielded conflicting results.…”

Precision management of localized prostate cancer

“…As described above, prostate MRI can accurately localize cancer lesions, but due to partial volume effects prostate MRI frequently underestimates tumor burden compared to whole mount histopathology [72, 73]. Considering this limitation, a reasonable peritumoral margin should be included when prostate MRI is used in planning for focal therapy as an alternative to definitive approaches such as surgery and radiotherapy.…”