SU‐E‐T‐236: Deconvolution of the Total Nuclear Cross‐Sections of Therapeutic Protons and the Characterization of the Reaction Channels

Abstract

Purpose:The knowledge of the total nuclear cross‐section Qtot(E) of therapeutic protons Qtot(E) provides important information in advanced radiotherapy with protons, such as the decrease of fluence of primary protons, the release of secondary particles (neutrons, protons, deuterons, etc.), and the production of nuclear fragments (heavy recoils), which usually undergo β+/− decay by emission of γ‐quanta. Therefore determination of Qtot(E) is an important tool for sophisticated calculation algorithms of dose distributions. This cross‐section can be determined by a linear combination of shifted Gaussian kernels and an error‐function. The resonances resulting from deconvolutions in the energy space can be associated with typical nuclear reactions.Methods:The described method of the determination of Qtot(E) results from an extension of the Breit‐Wigner formula and a rather extended version of the nuclear shell theory to include nuclear correlation effects, clusters and highly excited/virtually excited nuclear states. The elastic energy transfer of protons to nucleons (the quantum numbers of the target nucleus remain constant) can be removed by the mentioned deconvolution.Results:The deconvolution of the term related to the error‐function of the type cerf*er((E‐ETh)/σerf] is the main contribution to obtain various nuclear reactions as resonances, since the elastic part of energy transfer is removed. The nuclear products of various elements of therapeutic interest like oxygen, calcium are classified and calculated.Conclusions:The release of neutrons is completely underrated, in particular, for low‐energy protons. The transport of seconary particles, e.g. cluster formation by deuterium, tritium and α‐particles, show an essential contribution to secondary particles, and the heavy recoils, which create γ‐quanta by decay reactions, lead to broadening of the scatter profiles. These contributions cannot be accounted for by one single Gaussian kernel for the description of lateral scatter.