Metabolic response of non-Hodgkin's lymphoma to I-131-anti-B1 radioimmunotherapy: Evaluation with FDG PET

(131)-anti-B1 (CD20) radioimmunotherapy (RIT) is a promising approach for t reatment of non-Hodgkin's lymphoma (NHL). We assessed the tumor metabolic r esponse to RIT using FDG PET. Methods: We examined 14 patients with NHL, wh o were given first a tracer dose of 131I-anti-B1 and then RIT, each precede d by infusion of unlabeled anti-B1. In 8 of 14 patients, PET was performed at baseline and 33-70 d after RIT. The other 6 patients underwent PET at ba seline, 6-7 d after the tracer dose, and 5-7 d after RIT to estimate the ea rly response to tracer dose and RIT. To assess tumor FDG uptake, standardiz ed uptake value normalized for lean body mass (SUV-lean) was measured 1 h a fter FDG injection. Results: After RIT, complete response was observed in 6 patients, partial response in 6, and no response in 2. At 33-70 d after RI T, mean SUV-lean of 6 responders markedly declined to 41% of the baseline v alue (P < 0.002). Soon after tracer dose and after RIT, mean SUV-lean of th e other 6 responders decreased to 79% and 62% of the baseline values, respe ctively (P < 0.05). In 2 nonresponders, SUV-lean did not significantly decl ine from the baseline value at 37 d after RIT. Conclusion: FDG PET metaboli c data obtained 1-2 mo after RIT correlate well with the ultimate best resp onse of NHL to RIT, more significantly than the early data after tracer dos e or RIT. FDG uptake in NHL may decline gradually after RIT in responding p atients.