- Measurable disease is defined as at least one lesion that can be accurately measured in at least one dimension (longest dimension to be recorded); each lesion must be greater than or equal to 10 mm when measured by computed tomography (CT), positron emission tomography (PET)/CT or magnetic resonance imaging (MRI); lymph nodes must be greater than or equal to 15 mm in short axis when measured by CT, PET/CT, or MRI