Absorbed dose evaluation of Auger electron-emitting radionuclides: impact of input decay spectra on dose point kernels and S-values

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, namely 67Ga, 80mBr, 89Zr, 90Nb, 99mTc, 111In, 117mSn, 119Sb, 123I, 124I, 125I, 135La, 195mPt and 201Tl. 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.Comment: 27 pages, 4 figures, 3 table

IAEA coordinated research project on nuclear data for charged-particle monitor reactions and medical isotope production

An IAEA coordinated research project was launched in December 2012 to establish and improve the nuclear data required to characterise charged-particle monitor reactions and extend data for medical radionuclide production. An international team was assembled to undertake work addressing the requirements for more accurate cross-section data over a wide range of targets and projectiles, undertaken in conjunction with a limited number of measurements and more extensive evaluations of the decay data of specific radionuclides. These studies are nearing completion, and are briefly described below

Auger yield calculations for medical radioisotopes

Auger yields from the decays of 71Ge, 99mTc, 111In and 123–125I have been calculated using a Monte Carlo model of the Auger cascade that has been developed at the ANU. In addition, progress to improve the input data of the model has been made with the Multiconfiguration Dirac-Hartree-Fock method

Auger yield calculations for medical radioisotopes

Auger yields from the decays of 71Ge, 99mTc, 111In and 123–125I have been calculated using a Monte Carlo model of the Auger cascade that has been developed at the ANU. In addition, progress to improve the input data of the model has been made with the Multiconfiguration Dirac-Hartree-Fock method

Patients to Peers: Barriers and Opportunities for Doctors with Disabilities

Electron capture on $^{20}$Ne is thought to play a crucial role in the final evolution of electron-degenerate ONe stellar cores. Recent calculations suggest that the capture process is dominated by the second-forbidden transition between the ground states of $^{20}$Ne and $^{20}$F, making an experimental determination of this transition strength highly desirable. To accomplish this task we are refurbishing an intermediate-image magnetic spectrometer capable of focusing 7 MeV electrons, and designing a scintillator detector surrounded by an active cosmic-ray veto shield, which will serve as an energy-dispersive device at the focal plane.Comment: 4 pages, 1 figure, NIC-XI

A stochastic cascade model for Auger-electron emitting radionuclides

To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Sch€onfeld’s algorithms and the BRICC code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z¼1–100. Atomic transition energies were evaluated using a relativistic Dirac- Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of 123I, 124I, and 125I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study

Table of radionuclides (Vol. 8 - A = 41 to 198)

International audienceThe purpose of this monograph, number 5 of the series, is to present the recommended values of nuclear and decay data for a wide range of radionuclides. Activity measurements for more than sixty-three of these radionuclides have already been the subject of comparisons under the auspices of the Section II (dedicated to the measurement of radionuclides) of the CCRI. The material for this monograph is now covered in seven volumes. The first two volumes contain the primary recommended data relating to half-lives, decay modes, x-rays, gamma-rays, electron emissions, alpha- and beta-particle transitions and emissions, and their uncertainties for a set of sixty-eight radionuclides, Volume 1 for those radionuclides with mass number up to and including 150 and Volume 2 for those radionuclides with mass number over 150. Volume 3 contains the equivalent data for twenty-six additional radionuclides as listed and re-evaluation for 125Sb and 153Sm. Volume 4 contains the data for a further thirty-one radionuclides with re-evaluation for 226Ra. Volume 5 includes seventeen new radionuclide evaluations and eight re-evaluations of previous data as identified in the contents pages. Volume 6 contains twenty-one new radionuclide evaluations and four re-evaluations for 64Cu, 236Np, 237Np and 239U. Volume 7 contains twenty-four new radionuclide evaluations and five re-evaluations for 67Ga, 208Tl, 228 Th, 242Cm and 244Cm. Volume 8 contains twenty-three new radionuclide evaluations and nine re-evaluations for 88Y, 93mNb, 109Cd, 131I, 131mXe, 133Ba, 140Ba, 140La and 198au. The data have been collated and evaluated by an international working group (Decay Data Evaluation Project) led by the Laboratoire National de métrologie et d'Essais - Laboratoire national Henri Becquerel (LNE-LNHB). The evaluators have agreed on the methodologies to be used and their comments for each radionuclide in addition to the data tables in the present monograph can now both be found on the BIPM website at http://www.bipm.org/en/publications/scientific-output/monographies-ri.html. Consequently, the CD-ROM that accompanied previous issues is no longer deemed necessary and has been discontinued

A benchmarking study of Geant4 for Auger electrons emitted by medical radioisotopes

Auger emitting radioisotopes are of great interest in targeted radiotherapy because, once internalised in the tumour cells, they can deliver dose locally to the radiation sensitive targets, while not affecting surrounding cells. Geant4 is a Monte Carlo code widely used to characterise the physics mechanism at the basis of targeted radiotherapy. In this work, we benchmarked the modelling of the emission of Auger electrons in Geant4 deriving from the decay of 123I, 124I, 125I radionuclides against existing theoretical approaches. We also compared Geant4 against reference data in the case of 131Cs, which is of interest for brachytherapy. In the case of 125I and 131Cs, the simulation results are compared to experimental measurements as well. Good agreement was found between Geant4 and the reference data. As far as we know, this is the first study aimed to benchmark against experimental measurements the emission of Auger electrons in Geant4 for radiotherapy applications