Purpose: Based on the International Harmonization Project (IHP) criteria, positron emission tomography (PET) response assessment of residual nodal masses in patients with lymphoma after completion of therapy is performed visually using mediastinal blood pool as the reference. The primary objective of this study was to define the optimal reference for PET response assessment. Secondary aim was to assess if morphological criteria on computed tomography (CT) may improve performance of PET.
Methods: This institutional review board approved retrospective study included 137 patients, with Hodgkin's (n = 43) or non-Hodgkin's lymphoma (n = 94) assessed for residual masses (n = 180) after completion of therapy with pathology and clinical and imaging surveillance data (mean, 19 months) as the standard of reference. Two readers independently assessed response by IHP and Deauville criteria. The addition of morphological parameters on CT was assessed in relation to therapy response.
Results: Based on the standard of reference, 36 patients (26.3 %) had residual lymphoma. For IHP and Deauville criteria, sensitivity, specificity and accuracy were 97.2 %, 97.2 % (p = 1); 79.2 %, 92.1 % (p < 0.001); and 83.9 %, 93.4 % (p = 0.001), respectively. Of the morphological parameters assessed, only change in size over course of therapy was significant (p < 0.003) and improved specificity for IHP-based interpretation to 90.4 % (p = 0.008).
Conclusions: Using liver as the visual reference to determine PET positivity for lymphoma patients being assessed for residual masses at the end of therapy improves specificity, yet maintains the high sensitivity of PET in identifying residual disease. The addition of change in size after therapy improves specificity of PET when using IHP-based but not Deauville-based interpretation.
Keywords: Computed tomography; Fluorodeoxyglucose F18; Lymphoma; Positron emission tomography; Response; Therapy.