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, namely Ga,Br, Zr,Nb, Tc,In, Sn,Sb, I,I, I,La, Pt andTl. 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.

Subcellular Targeting of Theranostic Radionuclides

“…Energy and dose-deposition profiles for various radionuclides in spherical water volumes up to 100 μm in diameter. Calculations for electrons are based on a Monte Carlo method described by Falzone et al (2017) . Energy deposition by α-particles and recoiling daughter nuclei is derived from the NIST ( Berger et al, 2005 ) and SRIM ( Ziegler et al, 2010 ) stopping power data, respectively, and a straight projectile is assumed.…”

Targeting Micrometastases: The Effect of Heterogeneous Radionuclide Distribution on Tumor Control Probability

“…Absorbed fractions ( S -values) were calculated with the self-contribution (self-dose) to total S -values for each source cell, i.e. the dose from the surface of a source cell to its nucleus (N←Cs), the cytoplasm to its nucleus (N←Cy), and the nucleus to itself (N←N), derived from dose-point kernels of 111 In in liquid water using the terminology described in (4). The cross-dose was derived from the difference between the self-dose and simulated total dose (26).…”

“…It is postulated that short-range electron-emitting radionuclides that bind to or intercalate into the DNA are ideal for targeted radionuclide therapy (TRT) of single cells, limited volume disseminated cancer and micrometastases (1, 2). This hypothesis is based on the high linear-energy transfer (LET) (4–26 keV/μm) of the low energy Auger electrons (AE) that deposit energy within a few cubic nanometers of the decay site (3, 4). The localized absorption of multiple low energy electrons results in complex irreparable DNA damage (5).…”

The Heavy Ion Accelerator Facility: Research Achievements and Aspirations

“…The HIAF supports Australia's only experimental nuclear physics program (both fundamental and applied), a major accelerator mass spectrometry program, and facilities for ion-beam modification and analysis of materials. Newer initiatives include aspects of radiobiology [1][2][3], and detector characterisation for Australia's growing contributions to dark matter particle physics research, particularly for the SABRE experiment [4][5][6].…”