Diagnostic contribution of contrast-enhanced CT as compared to unenhanced low-dose CT in PET/CT staging and treatment response assessment of 18FDG-avid lymphomas: A prospective study

Objective: The aim of this study was to assess the added diagnostic value of contrast-enhanced CT (CECT) as compared to unenhanced CT (UECT) in PET/CT staging and treatment response assessment of 18FDG-avid lymphomas. Methods: 170 PET/UECT followed by CECT scans were prospectively performed for staging (n=85) and for treatment response assessment (n=85) of 18FDG-avid lymphomas, during a single session using an integrated 64-slice PET/CT scanner. CECT and UECT images were evaluated separately by two radiologists, whereas PET images by two nuclear physicians. Nodal and extranodal UECT and CECT findings were classified according to the Lugano criteria, and successively compared with PET/CT results, considered the gold standard. In the analysed groups, the agreement rate with the disease status determined via PET was calculated separately for UECT and CECT using Mc Nemar’s test on paired data. The added value of the contrast medium was shown by the agreement between the PET and CECT results and the lack of agreement between UECT and PET. Results: CECT enabled the identification of additional extranodal lesions (hepatic, muscular and gastric) in only 3 staging group cases (3.5%), indicating different stages as compared to UECT, whereas there was absolute agreement between CECT and UECT in terms of treatment response assessment. The added diagnostic value of CECT was lower than the established threshold for clinical relevance (15%). Mc Nemar’s test indicated no statistical significance in either group. The incidental findings detected by CECT but not UECT were important for clinical management, but not sufficient to alter lymphoma treatment strategy. Conclusion: According to our results, it might be possible to exclude CECT examination of 18FDG-avid lymphoma from staging and treatment response assessment, with the consequent advantages of reducing radiation exposure and potential contrast-related risks.