Computed tomography, magnetic resonance imaging and positron emission tomography in non-Hodgkin's lymphoma

Certain aspects of the use of CT, MR imaging and PET were evaluated in patients with non-Hodgkin's lymphoma (NHL) with the aim of determining whether these methods may provide practical guidance for improving the management of these patients. Subjective evaluation of the tumor pattern on CT images, and quantification of tracer uptake using 11C methionine (11C Met) and [18F] fluorodeoxyglucose (18FDG) PET in patients with NHL, were performed to determine their relations to malignancy grade. An inhomogeneous tumor pattern (I) was found on CT in 75% of high-grade tumors, whereas 68% of low-grade tumors were homogeneous (H). Sixteen (94%) of the 17 tumors with a severely inhomogeneous pattern (I) were high-grade NHL, while 22 (72%) of the 29 homogeneous tumors (H) were low-grade. All tumors were clearly visualized with both 11C Met and 18FDG PET. The uptake values for 18FDG were significantly-higher in high- than in low-grade tumors, while no significant differences between the prognostic groups were found for 11C Met. A subjective evaluation of the tumor pattern on CT and on MR images was performed. An inhomogeneity index (IH8) was also used in MR images to make a quantitative assessment of the degree of inhomogeneity to determine their relation to prognosis. Patients with localized NHL, treated with radiotherapy, had an excellent prognosis irrespective of the degree of inhomogeneity, while patients with generalized disease, treated with chemotherapy, had a poor prognosis if the tumors were heterogeneous. Among chemotherapy-treated patients, all 9 patients with high IH8 values (> 2.56) on MR images and 9 out of 11 patients with severe inhomogeneities on CT images died. All patients with gastric NHL except for one patient with low-grade NHL of the MALT type displayed high 18FDG uptake at PET corresponding to the pathological findings at endoscopy and/or CT. 18FDG correctly excluded gastric NHL in a patient with benign gastric ulcer, but was unable to discriminate between gastric NHL and gastric carcinoma. The results suggest that 18FDG PET may demonstrate the extension of NHL in the gastric wall more accurately than CT and endoscopy. The prognostic importance of the size of a residual mass after completion of chemotherapy, and of tumor regression rates during chemotherapy, was evaluated in patients with high-grade NHL. Neither a large tumor size before treatment nor a large residual tumor after treatment correlated with relapse. It appears, however, as if the response rate halfway through the therapy may predict the recurrence rate, although statistical significance was not reached.