Early response assessment using 3′-deoxy-3′-[ ¹⁸F]fluorothymidine-positron emission tomography in high-grade non-Hodgkin's lymphoma

Purpose: To evaluate 3′-deoxy-3′-[¹⁸F] fluorothymidine-positron emission tomography (FLT-PET) for early monitoring response of high-grade non-Hodgkin's lymphoma to treatment with cyclophosphamide-adriamycin-vincristine-prednisone chemotherapy with or without rituximab immunotherapy (R-CHOP/CHOP). Experimental Design: Twenty-two patients with histologically proven high-grade non-Hodgkin's lymphoma scheduled to undergo first line treatment with R-CHOP/CHOP were included. All patients received baseline imaging before therapy with FLT-PET. For noninvasive assessment of treatment response, FLT-PET was repeated at following time points: group 1 (n = 6), 1 and 6 weeks after R-CHOP/CHOP; group 2 (n = 16), 2 days after rituximab and 2 days after CHOP application. Emission images were acquired 45 min after injection of 300 to 370 MBq of FLT. FLT uptake was quantified by region-of-interest technique on a lesion basis. Maximum standardized uptake values (SUV) for FLT were calculated using circular region of interest (diameter, 1.5 cm). Results: In all patients, morphologically proven lesions showed initially high FLT uptake (mean SUV, 8.1 ± 3.9). In group 1, mean FLT SUV decreased 7 days after R-CHOP/CHOP by 77% (P < 0.001), the reduction in FLT SUV from baseline was 85% after 40 days (P = 0.003). In group 2, FLT uptake in patients without dexamethasone pretreatment revealed no significant reduction after rituximab (P = 0.3) but significantly decreased 2 days after CHOP to 32% compared with the baseline value (P = 0.004 ). Conclusions: Administration of R-CHOP/CHOP is associated with an early decrease in lymphoma FLT uptake. Interestingly, there was no reduction of FLT uptake after rituximab alone, indicating no early antiproliferative effect of immunotherapy. FLT-PET seems to be promising for early evaluation of drug effects in lymphoma.