Fluorodeoxyglucose positron emission tomography/computerized tomography (18FDG PET/CT) [1] is a powerful imaging modality in the field of oncology since it detects the enhanced glycometabolic activity of neoplastic cells, with the ability to define tumor burden and involved organs. Its role in managing lymphoma patients has grown progressively, and its use is now often recommended in [2,3,4,5], monitoring the therapy [6,7,8,9,10,11,12,13,14,15], and its modeling [16].
So far, only few studies in literature focused on the role of 18FDG PET during follow-up, especially its capability to detect relapse earlier with respect to CT or ultrasound imaging issue. The conclusions are not definite, raising the concern about sensitivity and specificity of the technique in this setting and the need of histological verification of 18FDG PET positivity [1]. In aggressive lymphomas, earlier detection is important since a timely salvage treatment is related to better outcome. Thus, analyzing 18FDG PET positivity patterns during follow-up to distinguish patients who should be referred to an immediate surgical biopsy to start further treatment from patients who could be managed with a more conservative observational approach that could be repeating imaging after 2 or 3 months to confirm or avoid biopsy [2, 4].
The clinical response based on PET-CT scans was defined in 2007 by the International Harmonization Project criteria [3, 4], and interpretation of PET was subsequently standardized by the proposal of the Deauville criteria for grading the degree of FDG avidity in comparison to the mediastinal blood pool and liver [5]. The Lugano classification, published in 2014, aimed to simplify and standardize baseline and response assessment and confirm the role for FDG PET-CT in lymphoma. Current study will assess the role of functional imaging with FDG PET-CT in lymphoma at the end of treatment and follow-up [17].
The most recent system proposed for response assessment, known as the Lugano classification [17], applies to both Hodgkin and non-Hodgkin lymphoma. The use of standardized criteria for response assessment is important for making accurate treatment decisions and for determining the direction of further research. This review provides an overview of the updated PET-CT response criteria to familiarize the radiologist with the most important and clinically relevant aspects of lymphoma imaging [15, 16].
The Lugano classification proposes new definitions relevant to imaging in lymphoma: for splenomegaly, vertical length of spleen greater than 13 cm; for measurable adenopathy, nodal long-axis diameter greater than 1.5 cm (a unidimensional measurement) [5,6,7,8,9,10].
Response at FDG PET/CT is graded on the five-point scale and categorized as complete metabolic response (scores 1, 2, 3), partial metabolic response (score 4 or 5 with reduced FDG uptake), no metabolic response (score 4 or 5 with no significant change in FDG uptake), or progressive metabolic disease (score 4 or 5 with increased FDG uptake or new lesions compared to previous scan) [3, 4].