90Y Bremsstrahlung imaging for absorbed-dose assessment in high-dose radioimmunotherapy

This feasibility study demonstrates 90Y quantitative bremsstrah-lung imaging of patients undergoing high-dose myeloablative 90Y-ibritumomab treatment. Methods: The study includes pre-therapy 111In SPECT/CT and planar whole-body (WB) imaging at 7 d and therapy 90Y SPECT/CT at 6 d and 90Y WB imaging at 1 d. Time–activity curves and organ-absorbed doses derived from 90Y SPECT images were compared with pretherapy 111In estimates. Organ activities derived from 90Y WB images at the first day were compared with corresponding pretherapy esti-mates. Results: Pretherapy 111In images from 3 patients were similar to the 90Y images. Differences between absorbed-dose estimates from pretherapy 111In and 90Y 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 differ-ences in pharmacokinetics between pretherapy and therapy. Conclusion: Quantitative bremsstrahlung imaging to estimate organ activities and absorbed doses is feasible