Early response to chemotherapy in malignant pleural mesothelioma assessed using diffusion-weighted MRI: Initial observations

Abstract Introduction We compared the MRI total tumour volume (TTV) and median apparent diffusion coefficient (ADC) of malignant pleural mesothelioma (MPM) before and at 4 weeks after chemotherapy, to determine whether these are potential early markers of treatment response. Methods Diffusion-weighted MRI (DWI) was performed in 23 patients with MPM before and after 4 weeks of chemotherapy. The TTV was measured by semi-automatic segmentation (GrowCut) and transferred onto ADC maps to record the median ADC. Test-retest repeatability of TTV and ADC was assessed in 8 patients. TTV and median ADC changes were compared between responders and non-responders, defined using modified RECIST on CT at 12 weeks after treatment. TTV and median ADC were also correlated with CT size measurement and disease survival. Results The test-retest 95% limits of agreement for TTV were -13.9% to 16.2 %; and for median ADC -1.2% to 3.3%. A significant increase in median ADC in responders was observed at four weeks after treatment (p=0.02). Correlation was found between CT tumour size change at 12 weeks and median ADC changes at four weeks post-treatment (r=-0.560, p=0.006). An increase in median ADC > 5.1% at 4 weeks has 100% sensitivity and 90% specificity for responders (AUC=0.933, p Conclusion DWI measurements of TTV and median ADC in MPM have good measurement repeatability. Increase in ADC at four weeks post-treatment has the potential to be an early response biomarker.