90Y Bremsstrahlung Imaging for Absorbed-Dose Assessment in High-Dose Radioimmunotherapy

This feasibility study demonstrates Y-90 quantitative bremsstrahlung imaging of patients undergoing high-dose myeloablative Y-90-ibritumomab treatment. Methods: The study includes pretherapy In-111 SPECT/CT and planar whole-body (WB) imaging at 7 d and therapy Y-90 SPECT/CT at 6 d and Y-90 WB imaging at 1 d. Time-activity curves and organ-absorbed doses derived from Y-90 SPECT images were compared with pretherapy In-111 estimates. Organ activities derived from Y-90 WB images at the first day were compared with corresponding pretherapy estimates. Results: Pretherapy In-111 images from 3 patients were similar to the Y-90 images. Differences between absorbed-dose estimates from pretherapy In-111 and Y-90 therapy were within 25%, except for the lungs. Corresponding activity differences derived from WB images were within 25%. Differences were ascribed to incomplete compensation methods and real differences in pharmacokinetics between pretherapy and therapy. Conclusion: Quantitative bremsstrahlung imaging to estimate organ activities and absorbed doses is feasible.