title: Organ-specific SPECT activity calibration using 3D printed phantoms for molecular radiotherapy dosimetry.
abstract: BACKGROUND
  Patient-specific absorbed dose calculations for molecular radiotherapy require accurate activity quantification. This is commonly derived from Single-Photon Emission Computed Tomography (SPECT) imaging using a calibration factor relating detected counts to known activity in a phantom insert.
  
  
  METHODS
  A series of phantom inserts, based on the mathematical models underlying many clinical dosimetry calculations, have been produced using 3D printing techniques. SPECT/CT data for the phantom inserts has been used to calculate new organ-specific calibration factors for (99m) Tc and (177)Lu. The measured calibration factors are compared to predicted values from calculations using a Gaussian kernel.
  
  
  RESULTS
  Measured SPECT calibration factors for 3D printed organs display a clear dependence on organ shape for (99m) Tc and (177)Lu. The observed variation in calibration factor is reproduced using Gaussian kernel-based calculation over two orders of magnitude change in insert volume for (99m) Tc and (177)Lu. These new organ-specific calibration factors show a 24, 11 and 8 % reduction in absorbed dose for the liver, spleen and kidneys, respectively.
  
  
  CONCLUSIONS
  Non-spherical calibration factors from 3D printed phantom inserts can significantly improve the accuracy of whole organ activity quantification for molecular radiotherapy, providing a crucial step towards individualised activity quantification and patient-specific dosimetry. 3D printed inserts are found to provide a cost effective and efficient way for clinical centres to access more realistic phantom data.
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK. andrew.paul.robinson@manchester.ac.uk.
authors.forename: Andrew P
authors.identifier: http://orcid.org/0000-0002-2510-1321
authors.initials: AP
authors.lastname: Robinson
authors.affiliation: Christie Medical Physics and Engineering (CMPE), The Christie NHS Foundation Trust, Wilmslow Road, Manchester, M20 4BX, UK.
authors.forename: Jill
authors.initials: J
authors.lastname: Tipping
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Cullen
authors.affiliation: Christie Medical Physics and Engineering (CMPE), The Christie NHS Foundation Trust, Wilmslow Road, Manchester, M20 4BX, UK.
authors.forename: David
authors.initials: D
authors.lastname: Hamilton
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Brown
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Flynn
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Oldfield
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.|Christie Medical Physics and Engineering (CMPE), The Christie NHS Foundation Trust, Wilmslow Road, Manchester, M20 4BX, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Page
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Emlyn
authors.initials: E
authors.lastname: Price
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Andrew
authors.identifier: http://orcid.org/0000-0002-2510-1321
authors.initials: A
authors.lastname: Smith
authors.affiliation: Schuster Laboratory, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Snee
keywords: 3D printing; Absorbed dose; Activity quantification; Molecular radiotherapy; SPECT