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$β^+$ radioactive nuclei created during proton therapy

Izabela Skwira-Chalot, Przemysław Sekowski, Agata Taranienko, Adam Spyra, Tomasz Matulewicz, Jan Swakoń, Joanna Matulewicz

TL;DR

This work addresses beam-range verification in proton therapy by quantifying proton-induced production of beta+-emitting nuclei $^{11}$C, $^{13}$N, and $^{15}$O in tissue-relevant elements. Using stacks of solid targets (C, BN, $SiO_2$) irradiated at $E_p<58$ MeV and detecting $511$ keV annihilation photons with $LaBr_3$ detectors, the authors extract cross sections with percent-level precision. The results generally reproduce the excitation function from prior studies across C, N, O and tissue, with detailed comparisons in each material and tissue type. They emphasize the practical significance for PET-based beam tracking, report some neutron-induced observations, and advocate a PDG-like dedicated evaluation group to standardize cross-section data for tissue-relevant reactions.

Abstract

During proton therapy, the beam flux decreases due to inelastic interactions with nuclei. At the highest energies used in proton therapy around 25\% protons initiate nuclear reactions. This report presents the cross section measurements of proton-induced production of three $β^+$ emitters -- $^{11}$C, $^{13}$N, $^{15}$O -- with half-lives between 2 and 20 minutes, using solid C, BN and SiO$_2$ targets. Stacks of up to 15 targets were irradiated simultaneously with proton beams of kinetic energy below 58 MeV at the AIC-144 cyclotron of the Institute of Nuclear Physics, Polish Academy of Sciences. The measured cross sections follow the excitation function obtained in the previous experiments, with uncertainty of a few percent.

$β^+$ radioactive nuclei created during proton therapy

TL;DR

This work addresses beam-range verification in proton therapy by quantifying proton-induced production of beta+-emitting nuclei C, N, and O in tissue-relevant elements. Using stacks of solid targets (C, BN, ) irradiated at MeV and detecting keV annihilation photons with detectors, the authors extract cross sections with percent-level precision. The results generally reproduce the excitation function from prior studies across C, N, O and tissue, with detailed comparisons in each material and tissue type. They emphasize the practical significance for PET-based beam tracking, report some neutron-induced observations, and advocate a PDG-like dedicated evaluation group to standardize cross-section data for tissue-relevant reactions.

Abstract

During proton therapy, the beam flux decreases due to inelastic interactions with nuclei. At the highest energies used in proton therapy around 25\% protons initiate nuclear reactions. This report presents the cross section measurements of proton-induced production of three emitters -- C, N, O -- with half-lives between 2 and 20 minutes, using solid C, BN and SiO targets. Stacks of up to 15 targets were irradiated simultaneously with proton beams of kinetic energy below 58 MeV at the AIC-144 cyclotron of the Institute of Nuclear Physics, Polish Academy of Sciences. The measured cross sections follow the excitation function obtained in the previous experiments, with uncertainty of a few percent.

Paper Structure

This paper contains 8 sections, 1 equation, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental procedure
  3. Experimental results
  4. Carbon
  5. Nitrogen
  6. Oxygen
  7. Tissue
  8. Conclusions

Figures (3)

  • Figure 1: The experimental set-up. The rotating wheel (moved with a stepping motor) provides space for up to 16 irradiated targets. They are positioned, in a predefined experimental sequence, between 3 pairs of scintillation detectors.
  • Figure 2: The measured activity of an irradiated tissue sample, interpreted as the sum of $^{11}$C, $^{13}$N and $^{15}$O decays. The uncertainty is statistical only. The time scale starts at the end of irradiation of the sample.
  • Figure 3: The activity of the bone samples irradiated by protons, measured at the end of the irradiation with 100 Gy dose (preliminary results). The uncertainties come from the precision the decay curve was decomposed.