Fig 1. Three enhancing foci in a patient with glioblastoma illustrate issues with lesion measurement during clinical trials. Lesion A is homogeneously enhancing and exceeds 10 mm in diameter and thus is ideal for serial measurement by RECIST or 1D (lower left), Macdonald or 2D (lower right), and volumetric (upper right) approaches. Lesion B is predominantly necrotic and is amenable to volumetric measurement (upper right) because the enhancing and nonenhancing components can be segmented. Lesion C is too small in diameter (8 mm) for accurate serial measurement and should be followed as a nonmeasurable lesion (see text). Images are postgadolinium contrast-enhanced axial T1-weighted.