SPECT/CT 90Y-Bremsstrahlung images for dosimetry during therapy

BACKGROUND: the characteristics of (90)Y, suitable for therapy, are denoted by the lack of γ-emission. Alternative methods, using analogues labelled with (111)In or (86)Y, are generally applied to image (90)Y-conjugates, with some inevitable drawbacks. New generation SPECT/CT image systems offer improved Bremsstrahlung images. The intent of this brief communication is to show that high quality (90)Y-Bremsstrahlung SPECT-CT images can be obtained, allowing the biodistribution of pure β-emitter therapeutical agents to be evaluated, also during the course of therapy. METHODS: the hybrid system Siemens Symbia-T2 was used for the acquisition of images of a patient given 1.7 GBq of (90)Y-DOTATATE. The following parameters were set for SPECT: 80 (50%) and 120 (30%) keV energy windows; medium energy collimators; 128 × 128 matrix, 64 projections (40s/step). Low-dose CT was acquired (80 mAs) for attenuation correction. Images were reconstructed with the OSEM 3D-Fast algorithm. RESULTS: post-therapy SPECT-CT (90)Y-Bremsstrahlung images of a patient undergoing receptor peptide radionuclide therapy are presented. (90)Y-Bremsstrahlung images obtained are suitable for tumour and normal organ dosimetry, providing detailed information on biodistribution, comparable to (111)In-diagnostic images. CONCLUSIONS: the improved Bremsstrahlung images means that the diagnostic examinations can be used for patient recruitment and that dosimetry evaluation can be restricted only to treated patients. This could avoid the need for a different radionuclide or isotope to mimic therapy. The clinical impact might be notable, as dosimetry and toxicity information are essential in radionuclide therapy, especially in patients with risk factors.