Contrast Clearance Analysis

Brain metastases are common in lung cancer and increasingly treated using targeted stereotactic radiosurgery (SRS). Post-SRS changes (including radionecrosis) may be difficult to distinguish from progressive brain metastasis on MRI. This can have important implications for guiding the most appropriate further management. Contrast clearance analysis (CCA) presents an alternative imaging technique to aid differentiation of progressive tumour from post-treatment changes. In this study, we evaluate the role of CCA, assessing its utility in a real-world setting of patients with NSCLC treated for brain metastases. In particular, we assess the impact of CCA interpretations on treatment decisions and the effects of using this imaging technique with suggestions for best practices. Our experience shows CCA to be feasible and useful in patients with NSCLC in cases of diagnostic uncertainty in MRI. Recommendations include the appreciation of a thin rim of rapid contrast clearance, which can be seen in responding tumours, and the importance of the timing of CCA prior to surgery for suspected brain metastasis progression. Background and Objective: Brain metastases are common in lung cancer and increasingly treated using targeted radiotherapy techniques such as stereotactic radiosurgery (SRS). Using MRI, post-SRS changes may be difficult to distinguish from progressive brain metastasis. Contrast clearance analysis (CCA) uses T1-weighted MRI images to assess the clearance of gadolinium and can be thus used to assess vascularity and active tumours. Design and Methods: We retrospectively assessed CCAs in 62 patients with non-small cell lung cancer (NSCLC) undergoing 104 CCA scans in a single centre. Results: The initial CCA suggested the aetiology of equivocal changes on standard MRI in 80.6% of patients. In all patients whose initial CCA showed post-SRS changes and who underwent serial CCAs, the initial diagnosis was upheld with the serial imaging. In only two cases of a presumed progressive tumour on the initial CCA, subsequent treatment for radionecrosis was instigated; a retrospective review and re-evaluation of the CCAs show that progression was reported where a thin rim of rapid contrast clearance was seen, and this finding has been subsequently recognised as a feature of post-treatment change on CCAs. The lack of concordance with CCA findings in those who underwent surgical resection was also found to be due to the over-reporting of the thin blue rim as disease in th