Assessment of Metabolic Response to Radioimmunotherapy with Y-90-Ibritumomab Tiuxetan in Patients with Relapsed or Refractory B-Cell Non-Hodgkin Lymphoma

Purpose: To prospectively compare the assessment of metabolic response to yttrium 90 ( 90 Y)-ibritumomab tiuxetan radioimmunotherapy (RIT) by using fl uorine 18 ( 18 F) fl uorodeoxyglucose (FDG) combined positron emission tomographic- computed tomographic (PET/CT) imaging at 2 and 6 months to determine the most appropriate time to detect therapeutic response in refractory non-Hodgkin lymphoma (NHL) patients treated with RIT. Materials and Methods: The ethical committee of the university approved the protocol and all patients signed informed consent. Twentythree consecutive patients (10 women, 13 men; mean age, 51.8 years 6 7.3 [standard deviation ]) treated by using RIT for relapsed or refractory follicular NHL were enrolled. For all patients, 18 F FDG PET/CT scanning was performed at baseline and at 2 and 6 months after RIT. Response was assessed by using the International Workshop Criteria (IWC) and revised criteria (IWC + PET) as well as the criteria of the European Organization for Research and Treatment of Cancer. One-way analysis of variance for repeated measures, receiver operator curve analysis, and Kaplan-Meier curves were used for statistical analysis. Results: PET/CT performed at 2 months revealed complete ( n = 12) or partial ( n = 4) metabolic response in 16 of 23 patients with complete or partial clinical response. These fi ndings were all confi rmed at 6-month scanning. PET/CT indicated refractory or persistent disease at 2 and 6 months in the remaining seven patients. Better overall survival was observed for patients with a reduction in the maximum standard uptake value of 49% or higher (both at 2 and 6 months after RIT) when compared with those with a decrease of less than 49% ( P , .05). Conclusion: Early assessment of response to RIT by using PET/CT might be useful in the identifi cation of patients needing additional therapeutic strategies.