Objective: To assess the interobserver variability in the radiologic assessment of response to chemotherapy in patients with recurrent glioma.
Methods: Five clinicians with experience in the treatment and follow-up of patients with glioma measured tumor size in 20 pairs of CT and 20 pairs of MRI scans of 35 patients who had been treated with chemotherapy for recurrent glioma. Tumor size was defined as the product of the two largest perpendicular enhancing tumor diameters on the postcontrast images. To assess the interobserver variability in the measurements of tumor size, and in the classification according to the widely used Macdonald response criteria, intraclass correlation coefficients (ICC) and weighted kappa values were calculated.
Results: Substantial interobserver agreement was noted in the manual, two-dimensional measurements of tumor size on CT and MRI in patients treated with chemotherapy for recurrent glioma (overall ICC 0.64). Classification of response to chemotherapy according to the Macdonald criteria resulted in moderate interobserver agreement (overall weighted kappa 0.51). In 65% of evaluated CT and in 55% of evaluated MRI studies, no complete consensus was found for the categorical tumor response measurement.
Conclusion: The radiologic assessment of response to chemotherapy in patients with recurrent glioma is susceptible to considerable interobserver variability. This underlines the difficulties that arise in scoring response to chemotherapy by conventional radiologic techniques.