title: Characteristics of Bremsstrahlung emissions of (177)Lu, (188)Re, and (90)Y for SPECT/CT quantification in radionuclide therapy.
abstract: OBJECTIVE
  Beta particles emitted by radioisotopes used in targeted radionuclide therapies (TRT) create Bremsstrahlung (BRS) which may affect SPECT quantification when imaging these isotopes. The purpose of the current study was to investigate the characteristics of Bremsstrahlung produced in tissue by three β-emitting radioisotopes used in TRT.
  
  
  METHODS
  Monte Carlo simulations of (177)Lu, (188)Re, and (90)Y sources placed in water filled cylinders were performed. BRS yields, mean energies and energy spectra for (a) all photons generated in the decays, (b) photons that were not absorbed and leave the cylinder, and (c) photons detected by the camera were analyzed. Next, the results of simulations were compared with those from experiments performed on a clinical SPECT camera using same acquisition conditions and phantom configurations as in simulations.
  
  
  RESULTS
  Simulations reproduced relatively well the shapes of the measured spectra, except for (90)Y which showed an overestimation in the low energy range. Detailed analysis of the results allowed us to suggest best collimators and imaging conditions for each of the investigated isotopes. Finally, our simulations confirmed that the BRS contribution to the energy spectra in quantitative imaging of (177)Lu and (188)Re could be ignored.
  
  
  CONCLUSIONS
  For (177)Lu and (188)Re, BRS contributes only marginally to the total spectra recorded by the camera. Our analysis shows that MELP and HE collimators are the best for imaging these two isotopes. For (90)Y, HE collimator should be used.
authors.affiliation: Medical Imaging Research Group, University of British Columbia, Vancouver, British Columbia, Canada; Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: curibe@bccrc.ca.
authors.forename: Carlos F
authors.initials: CF
authors.lastname: Uribe
authors.affiliation: Medical Imaging Research Group, University of British Columbia, Vancouver, British Columbia, Canada; Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Esquinas
authors.affiliation: Vancouver Coastal Health Authority, Vancouver, British Columbia, Canada.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Gonzalez
authors.affiliation: Medical Imaging Research Group, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Anna
authors.initials: A
authors.lastname: Celler
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008187:Lutetium / Q000737:chemistry*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D011868:Radioisotopes / Q000737:chemistry* / Q000627:therapeutic use*; D012211:Rhenium / Q000737:chemistry*; D000072098:Single Photon Emission Computed Tomography Computed Tomography; D014867:Water / Q000737:chemistry; D015021:Yttrium Radioisotopes / Q000737:chemistry*
chemical_list: D011868:Radioisotopes; D015021:Yttrium Radioisotopes; D014867:Water; D008187:Lutetium; D012211:Rhenium
keywords: Bremsstrahlung; Energy spectrum; Imaging; Radioisotopes; Targeted radionuclide therapy