title: Absorbed dose evaluation of Auger electron-emitting radionuclides: impact of input decay spectra on dose point kernels and S-values.
abstract: The aim of this study was to investigate the impact of decay data provided by the newly developed stochastic atomic relaxation model BrIccEmis on dose point kernels (DPKs - radial dose distribution around a unit point source) and S-values (absorbed dose per unit cumulated activity) of 14 Auger electron (AE) emitting radionuclides, namely67Ga,80mBr,89Zr,90Nb,99mTc,111In,117mSn,119Sb,123I,124I,125I,135La,195mPt and201Tl. Radiation spectra were based on the nuclear decay data from the medical internal radiation dose (MIRD) RADTABS program and the BrIccEmis code, assuming both an isolated-atom and condensed-phase approach. DPKs were simulated with the PENELOPE Monte Carlo (MC) code using event-by-event electron and photon transport. S-values for concentric spherical cells of various sizes were derived from these DPKs using appropriate geometric reduction factors. The number of Auger and Coster-Kronig (CK) electrons and x-ray photons released per nuclear decay (yield) from MIRD-RADTABS were consistently higher than those calculated using BrIccEmis. DPKs for the electron spectra from BrIccEmis were considerably different from MIRD-RADTABS in the first few hundred nanometres from a point source where most of the Auger electrons are stopped. S-values were, however, not significantly impacted as the differences in DPKs in the sub-micrometre dimension were quickly diminished in larger dimensions. Overestimation in the total AE energy output by MIRD-RADTABS leads to higher predicted energy deposition by AE emitting radionuclides, especially in the immediate vicinity of the decaying radionuclides. This should be taken into account when MIRD-RADTABS data are used to simulate biological damage at nanoscale dimensions.
authors.affiliation: Department of Oncology, CR-UK/MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford, United Kingdom. Department of Biomedical Science, Tshwane University of Technology, Pretoria, South Africa.
authors.forename: Nadia
authors.initials: N
authors.lastname: Falzone
authors.forename: Boon Q
authors.initials: BQ
authors.lastname: Lee
authors.forename: José M
authors.initials: JM
authors.lastname: Fernández-Varea
authors.forename: Christiana
authors.initials: C
authors.lastname: Kartsonaki
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Stuchbery
authors.forename: Tibor
authors.initials: T
authors.lastname: Kibédi
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Vallis
mesh_terms: D065638:Absorption, Radiation; D004583:Electrons; D009010:Monte Carlo Method; D017785:Photons; D011829:Radiation Dosage; D011868:Radioisotopes / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000737:chemistry*
chemical_list: D011868:Radioisotopes; D019275:Radiopharmaceuticals