Multiparametric MRI in the assessment of response of rectal cancer to neoadjuvant chemoradiotherapy: A comparison of morphological, volumetric and functional MRI parameters.

PURPOSE

To compare morphological and functional MRI metrics and determine which ones perform best in assessing response to neoadjuvant chemoradiotherapy (CRT) in rectal cancer.

MATERIALS AND METHODS

This retrospective study included 24 uniformly-treated patients with biopsy-proven rectal adenocarcinoma who underwent MRI, including diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) sequences, before and after completion of CRT. On all MRI exams, two experienced readers independently measured longest and perpendicular tumour diameters, tumour volume, tumour regression grade (TRG) and tumour signal intensity ratio on T2-weighted imaging, as well as tumour volume and apparent diffusion coefficient on DW-MRI and tumour volume and transfer constant K on DCE-MRI. These metrics were correlated with histopathological percent tumour regression in the resected specimen (%TR). Inter-reader agreement was assessed using the concordance correlation coefficient (CCC).

RESULTS

For both readers, post-treatment DW-MRI and DCE-MRI volumetric tumour assessments were significantly associated with %TR; DCE-MRI volumetry showed better inter-reader agreement (CCC=0.700) than DW-MRI volumetry (CCC=0.292). For one reader, mrTRG, post-treatment T2 tumour volumetry and assessments of volume change made with T2, DW-MRI and DCE-MRI were also significantly associated with %TR.

CONCLUSION

Tumour volumetry on post-treatment DCE-MRI and DW-MRI correlated well with %TR, with DCE-MRI volumetry demonstrating better inter-reader agreement.

KEY POINTS

• Volumetry on post-treatment DCE-/DW-MRI sequences correlated well with histopathological tumour regression. • DCE-MRI volumetry demonstrated good inter-reader agreement. • Inter-reader agreement was higher for DCE-MRI volumetry than for DW-MRI volumetry. • DCE-MRI volumetry merits further investigation as a metric for evaluating treatment response.