Page 30 - 18F-FDG PET as biomarker in aggressive lymphoma; technical and clinical validation

Chapter 2
A short history
Major changes have taken place in the staging and response assessment of malignant lymphoma in the last two decades. With the introduction of fluorodeoxyglucose-positron emission tomography (FDG-PET) and positron emission tomography-computed tomography (PET-CT), the criteria for staging and monitoring response have changed dramatically. In the revised Cheson criteria published in 2007 [1], staging with FDG-PET was still optional, and end-of treatment assessment using FDG-PET and CT was obligatory for Hodgkin lymphoma (HL) and diffuse large B-cell lymphoma (DLBCL). In the Lugano criteria published in 2014 [2], PET-CT is recommended for staging as well as response assessment following therapy, as it is the most accurate imaging modality. However, one of the characteristics of (molecular) metabolic imaging is to be able to assess metabolic changes early in treatment. The question arises whether ‘interim’ FDG-PET-CT (iPET) can be used as a biomarker to differentiate good and poor responders during treatment, in order to modify therapy and to improve outcome. Recent clinical trials have addressed these questions, and we discuss the results and the implications for clinical practice.
Assessment of interim-PET scans
International guidelines recommend the use of a 5-point scale [also called the Deauville score (DS)] for grading FDG-uptake in lymphoma, compared to physiological uptake in the mediastinum and liver, for response assessment in daily practice and clinical trials [2-4]. No FDG uptake is graded as DS 1; uptake less than or equal in intensity to the mediastinum as DS 2; lesions with FDG uptake between mediastinum and liver are assessed as DS 3; uptake more intense than liver is scored as DS 4; and markedly increased uptake or new lymphoma- related lesions as DS 5 (Figure 1). This categorization has a high interobserver agreement in HL and DLBCL [5,6].
However, FDG-PET is also a quantitative imaging technique, allowing semi- quantitative imaging interpretation, using standardized uptake values (SUV). Reporting change of FDG uptake (usually expressed as a relative change) can also be used for interim response assessment. The reliability of the results depends on having comparable procedures for patient preparation and injection, and scanning
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