RT Journal Article SR Electronic T1 90Y-DOTATOC Dosimetry–Based Personalized Peptide Receptor Radionuclide Therapy JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1692 OP 1698 DO 10.2967/jnumed.117.202903 VO 59 IS 11 A1 Yusuf Menda A1 Mark T. Madsen A1 Thomas M. O’Dorisio A1 John J. Sunderland A1 G. Leonard Watkins A1 Joseph S. Dillon A1 Sarah L. Mott A1 Michael K. Schultz A1 Gideon K.D. Zamba A1 David L. Bushnell A1 M. Sue O’Dorisio YR 2018 UL http://jnm.snmjournals.org/content/59/11/1692.abstract AB Pretherapy PET with 86Y-DOTATOC is considered the ideal dosimetry protocol for 90Y-DOTATOC therapy; however, its cost, limited availability, and need for infusion of amino acids to mimic the therapy administration limit its use in the clinical setting. The goal of this study was to develop a dosimetric method for 90Y-DOTATOC using 90Y-DOTATOC PET/CT and bremsstrahlung SPECT/CT and to determine whether dosimetry-based administered activities differ significantly from standard administered activities. Methods: This was a prospective phase 2 trial of 90Y-DOTATOC therapy in patients with somatostatin receptor–positive tumors. 90Y-DOTATOC was given in 3 cycles 6–8 wk apart. In the first cycle of therapy, adults received 4.4 GBq and children received 1.85 GBq/m2; the subsequent administered activities were adjusted according to the dosimetry of the preceding cycle so as not to exceed a total kidney dose of 23 Gy and bone marrow dose of 2 Gy. The radiation dose to the kidneys was determined from serial imaging sessions consisting of time-of-flight 90Y-DOTATOC PET/CT at 5 h after therapy and 90Y-DOTATOC bremsstrahlung SPECT/CT at 6, 24, 48, and 72 h. The PET/CT data were used to measure the absolute concentration of 90Y-DOTATOC and to calibrate the bremsstrahlung SPECT kidney clearance data. The radiation dose to the kidneys was determined by multiplying the time-integrated activity (from the fitted biexponential curve of renal clearance of 90Y-DOTATOC) with the energy emitted per decay, divided by the mass of the kidneys. Results: The radiation dose to the kidneys per cycle of 90Y-DOTATOC therapy was highly variable among patients, ranging from 0.32 to 3.0 mGy/MBq. In 17 (85%) of the 20 adult patients who received the second and the third treatment cycles of 90Y-DOTATOC, the administered activity was modified by at least 20% from the starting administered activity. Conclusion: Renal dosimetry of 90Y-DOTATOC is feasible using 90Y-DOTATOC time-of-flight PET/CT and bremsstrahlung SPECT/CT and has a significant impact on the administered activity in treatment cycles.