Non-Hodgkin lymphoma and Hodgkin disease: coregistered FDG PET and CT at staging and restaging--do we need contrast-enhanced CT?

PURPOSE To retrospectively compare diagnostic value of coregistered fluorine 18 fluorodeoxyglucose positron emission tomographic (PET) and computed tomographic (CT) scans obtained with low-dose nonenhanced CT (PET/CT) with those routinely obtained with contrast material-enhanced CT for staging and restaging of disease in patients with Hodgkin disease or high-grade non-Hodgkin lymphoma. MATERIALS AND METHODS Sixty patients (mean age, 39.6 years +/- 17.1 [standard deviation]) with Hodgkin disease (n = 42) or high-grade non-Hodgkin lymphoma (n = 18) were included in this retrospective study. All patients underwent PET/CT and contrast-enhanced CT within a maximum of 24 days (mean, 9.1 days +/- 7.0) of each other for staging (n = 19) or first follow-up examination (n = 41). Findings were extracted from original written reports (PET/CT, contrast-enhanced CT) and compared with findings of reference standard, which included biopsy or follow-up with clinical, laboratory, or other imaging findings. For statistical analysis, sensitivity and specificity were calculated with findings of the reference standard. Agreement of both methods was determined with Cohen kappa and McNemar tests on a per-patient basis. RESULTS For evaluation of lymph node involvement, sensitivity of PET/CT and contrast-enhanced CT was 94% and 88%, and specificity was 100% and 86%, respectively. For evaluation of organ involvement, sensitivity of PET/CT and contrast-enhanced CT was 88% and 50%, and specificity was 100% and 90%, respectively. Agreement of both methods was excellent (kappa = 0.84) for assignment of lymph node involvement but only fair (kappa = 0.50) for extranodal disease. A difference with P <.05 (McNemar test) was considered significant in regard to exclusion of disease with PET/CT, compared with contrast-enhanced CT. CONCLUSION PET/CT performed with nonenhanced CT is more sensitive and specific than is contrast-enhanced CT for evaluation of lymph node and organ involvement, especially regarding exclusion of disease, in patients with Hodgkin disease and high-grade non-Hodgkin lymphoma.