Speakers
Description
Several studies show that the combination of high-Z nanoparticles (NPs) and external radiotherapy (RT) leads to an increased radiation effect in tumoral cells without an increase of the patient dose [1,2]. Among the various elements with sensitizing potential, Au NPs have been the most studied due to the greater biocompatibility of gold. In this technique, Au NPs are incorporated inside tumor cells with the aid of biomolecules with specific affinity for each cell type. Thus in an RT treatment it is possible to produce additional secondary radiation enhancement in the tumor tissues internalized with Au NPs. This additional radiation results mostly from electronic collisions of the external beam used in RT with the NPs. Particularly relevant is the ionization of internal atomic shells that lead to a cascade of transitions. The low-energy component of the Auger spectrum produces electrons with a very short range (smaller than the cell dimensions) and, therefore, contribute significantly to the local radiosensitizing effect of NPs.
Dosimetric calculations of RT with NPs are based on Monte Carlo (MC) simulations using well-known codes [3]. These typically use libraries of atomic parameters calculated several decades ago with outdated models. Since the low-energy component of the Auger spectrum is particularly sensitive to correlation effects, we present in this paper new calculations based on the Multiconfiguration Dirac-Fock method. For this, the code developed by Desclaux and Indelicato [4,5] was used to compute radiative and radiationless transition rates as well as photoionization cross-sections for different energies relevant in RT. The Auger spectrum is simulated using an MC-based method to produce the atomic de-excitation cascades. The impact of the new calculations will be discussed based on simulations of the radial dose profile in a water sphere using the TOPAS code [6,7].
References
[1] K. Haume et al. Cancer Nanotech. 7:1 (2016)
[2] S. Lacombe, E. Porcel, E. Scifoni. Cancer Nanotech. 8:9 (2017)
[3] S. Incerti et al. Nucl. Instrum. Methods. B 372:91–101 (2016)
[4] J.Desclaux, Comp. Phys. Commun. 9:31(1975)
[5] P. Indelicato, Phys. Rev. A 51:1132 (1995)
[6] J. Per et al. Med. Phys. 39(11):6818-37 (2012)
[7] B. Faddegon et al. Phys Med. 72:114-121 (2020)
