Dosimetry of 90Y-Ibritumomab Tiuxetan as Consolidation of First Remission in Advanced-Stage Follicular Lymphoma: Results from the International Phase 3 First-Line Indolent Trial

The objective of this analysis was to assess the radiation exposure associated with Y-90-ibritumomab tiuxetan when used as consolidation therapy in adults with low or minimal tumor burden after first-line therapy of advanced follicular lymphoma (FL). Methods: The patients who were enrolled in the phase 3 first-line indolent trial were 18 y or older, with CD20(+) grade 1 or 2 stage III or IV FL, and a partial response, complete response, or unconfirmed complete response to first-line chemotherapy. The patients were allocated randomly to receive a single infusion of unlabeled rituximab 250 mg/m(2) on day 27 and consolidation on day 0 with a single dose of Y-90-ibritumomab tiuxetan, 14.8 MBq/kg, immediately after unlabeled rituximab, 250 mg/m(2), or no further treatment. On day 27, a subset of patients received an injection of 185 MBq of In-111-ibritumomab tiuxetan immediately after unlabeled rituximab, 250 mg/m(2), for central dosimetry analysis. Correlations were assessed between organ radiation absorbed dose and toxicity, body weight, body mass index, and progression-free survival. Results: Central dosimetry evaluations were available from 57 of 70 patients. Median radiation absorbed doses were 100 cGy (range, 28-327 cGy) for the red marrow and 72 cGy (range, 46-106 cGy) for the whole body. Radiation absorbed doses did not differ significantly between patients who had a partial response or complete response to initial therapy. Progression-free survival correlated significantly with the whole-body (r = 0.4401; P = 0.0006) and bone marrow (r = 0.2976; P = 0.0246) radiation dose. Body weight was significantly negatively correlated with whole-body radiation dose (r = 20.4971; P < 0.0001). Neither the whole-body radiation dose nor the bone marrow radiation dose correlated with hematologic toxicity. Conclusion: In patients with low or minimal residual tumor burden after first-line chemotherapy of advanced FL, whole-body and bone marrow exposure after Y-90-ibritumomab tiuxetan consolidation showed a significant positive correlation with progression-free survival, whereas dosimetric data could not predict hematologic toxicity.