Page 14 - 18F-FDG PET as biomarker in aggressive lymphoma; technical and clinical validation

Chapter 1
of CT for evaluation of intrathoracic and infradiafragmatic lymph nodes [18]. The use of baseline [18F]FDG PET/CT led to a higher sensitivity especially for extranodal disease compared to CT (e.g. bone marrow, liver/spleen involvement) [19]. The international harmonization project (IHP) criteria strongly encouraged the use of baseline [18F]FDG PET when [18F]FDG PET is used for response assessment [20]. Since the Lugano classification guidelines in 2014, baseline [18F] FDG PET has a firm role for the staging of all [18F]FDG avid lymphomas such as HL and DLBCL according to a modified Ann Arbor staging system [16,21,22]. The Lugano classification guidelines contain recommendations for the initial evaluation, staging and response evaluation for both HL and NHL.
End-of-treatment response assessment
The use of [18F]FDG PET for response assessment after treatment in lymphoma led to the revision of the International Working Group criteria [23] by the IHP imaging committee [20]. The IHP criteria were the first criteria for lymphoma patients based on the visual interpretation of [18F]FDG PET scans that were recommended in clinical guidelines [20]. These criteria dichotomized end-of-treatment [18F]FDG PET results into positive and negative based on an assessment of [18F]FDG uptake in the tumor compared to the mediastinal blood pool activity or the surrounding normal background in lesions smaller than 2 cm [20]. Nowadays, [18F]FDG PET/CT is the standard for the end-of-treatment response assessment in DLBCL and HL and should be assessed according to the Lugano classification guidelines [21,22].
Interim response assessment by [18F]FDG PET
In the search for an early predictor of outcome to distinguish responders from non‐responders, interim [18F]FDG PET response assessment has been identified as a very promising tool.The hypothesis is that response to R-CHOP treatment can be predicted using interim [18F]FDG PET, i.e. PET during treatment. Conceptually, it provides an excellent basis for ‘personalized medicine’, where DLBCL patients without sufficient response (i.e. positive interim [18F]FDG PET scan) may be shifted early during R-CHOP treatment to another potentially curative therapy. In this way effectiveness of therapy is maximized, while unnecessary delays, toxicity and costs are minimized. For HL a PET guided approach is nowadays common practice in the Netherlands and recommended internationally (if PET is available), with an interim PET after 2 cycles of treatment [24,25].
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