Electron emission spectra from gold-nanoparticles for dose estimation in radiation therapy

• Applicant: Dr. Hans Rabus, since 4/2020
• Subject Area: Experimental Condensed Matter Physics ; Nuclear Medicine, Radiotherapy, Radiobiology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 386872118

Radiotherapy is one of the most common modalities for cancer treatment. As the radiation passes through cells and tissues, it deposits energy and forms ions which can result in cancer cell death. Such cytotoxic effects are initiated by the primary particle and even more by secondary electrons. Because ionizing processes are not cell specific and damage tumor and healthy cells alike, a deposition of radiation absorbing elements into the tumor can sensitize it to radiation, which effectively reduces the dose to healthy tissue. Studies have shown that the use of gold nanoparticles can produce a dose enhancement for irradiation with X-rays [1] and proton beams [2]. Due to the steep dose gradient in the vicinity of nanoparticles, conventional macroscopic dosimetry is insufficient for the characterization of dose distribution. Monte Carlo track structure simulations are therefore required to account for localized nanoscopic interactions of secondary electrons [3]. These simulations are currently based in simplified theoretical scattering models, which are no longer valid for energies below a few keV resulting in extrapolations with large uncertainties. In the case of water (often used as a substitute for biological matter), these models could be adjusted to experimental data so that the simulation is valid for microscopic applications [4]. For gold, however, the required atomic scattering cross sections cannot be obtained experimentally, but experimental electron spectra from gold nanoparticles can be used to benchmark the simulated data, and thus, reduce the uncertainty of subsequent dose calculations.Measured electron spectra from gold nanoparticles were recently reported for low keV energies, where the agreement with Geant4 MC simulation was poor [5]. To account for the localized dose-enhancement at therapeutic X-ray energies, it is crucial to investigate electron emission at photon energies sufficient to trigger a large Auger cascade with many low-energy secondary electrons. The energy loss and self-absorption of electrons within the gold nanoparticle should also be determined, in terms of the particle size.The resent proposal aims to measure energy spectra of electrons emitted from gold nanoparticles of different size for X-rays and proton beam irradiation. The proposed X-ray energies are above the gold L-edge (12 keV) and produced by a synchrotron and clinical X-ray sources. The proposed proton energy is 100 keV, which is within the Bragg-peak. The project will obtain important fundamental data to estimate the dose distribution and dose enhancement by gold nanoparticle and thereby promote the translation of such radiosensitizers into clinical applications.[1] J.F. Hainfeld et al., J. Pharm., 60, 977-85 (2008).[2] J.C. Polf et al., Appl. Phys. Lett., 98, 3-5 (2011).[3] H.N. McQuaid et al., Sci. Rep., 6, 19442 (2016).[4] S. Incerti et al., Med. Phys., 37, 4692-4708 (2010).[5] R. Casta et al., Phys. Med. Biol., 60, 9095-9105 (2015).

• DFG Programme: Research Grants
• Ehemalige Antragstellerinnen / Ehemalige Antragsteller: Dr. Heidi Nettelbeck, from 7/2019 until 4/2020; Dr. Benedikt Rudek, until 6/2019