February 26th, 2021

лошадь, диаграмма, Фейнман

Красивые картинки кривой Брэгга для терапии ионами углерода

Bragg-Curve Simulation of Carbon-Ion Beams for Particle-therapy Applications: a study with the GEANT4 toolkit^ https://arxiv.org/abs/2102.12743

M. Kh. Hamad
We used the GEANT4 Monte Carlo MC Toolkit to simulate carbon ion beams incident on water, tissue, and bone, taking into account nuclear fragmentation reactions. Upon increasing the energy of the primary beam, the position of the Bragg-Peak transfers to a location deeper inside the phantom. For different materials, the peak is located at a shallower depth along the beam direction and becomes sharper with increasing electron density NZ. Subsequently, the generated depth dose of the Bragg curve is then benchmarked with experimental data from GSI in Germany. The results exhibit a reasonable correlation with GSI experimental data with an accuracy of between 0.02 and 0.08 cm, thus establishing the basis to adopt MC in heavy-ion treatment planning. The Kolmogorov-Smirnov K-S test further ascertained from a statistical point of view that the simulation data matched the experimentally measured data very well. The two-dimensional isodose contours at the entrance were compared to those around the peak position and in the tail region beyond the peak, showing that bone produces more dose, in comparison to both water and tissue, due to secondary doses. In the water, the results show that the maximum energy deposited per fragment is mainly attributed to secondary carbon ions, followed by secondary boron and beryllium. Furthermore, the number of protons produced is the highest, thus making the maximum contribution to the total dose deposition in the tail region. Finally, the associated spectra of neutrons and photons were analyzed. The mean neutron energy value was found to be 16.29 MeV, and 1.03 MeV for the secondary gamma. However, the neutron dose was found to be negligible as compared to the total dose due to their longer range.
лошадь, диаграмма, Фейнман

О радиобиологических эффектах облучения с большой мощностью дозы

Хорошо изложено, начиная от радиолиза воды, подойдет освежить мои лекции.

Does FLASH deplete Oxygen? Experimental Evaluation for Photons, Protons and Carbon Ions: https://arxiv.org/abs/2102.12762

Jeannette Jansen (1,2), Jan Knoll (1,2), Elke Beyreuther (3,4), Jörg Pawelke (3,5), Raphael Skuza (1,2), Rachel Hanley (1,2), Stephan Brons (6), Francesca Pagliari (1), Joao Seco (1,2) ((1) Division of Biomedical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany, (2) Faculty of Physics and Astronomy, Ruprecht-Karls-University Heidelberg, Germany, (3) OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University, Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, (4) Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Radiation Physics, Dresden, Germany, (5) Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Radiooncology-OncoRay, Dresden, Germany, (6) Heidelberg Ion-Beam Therapy Center (HIT), Heidelberg, Germany)
Purpose: To investigate experimentally, if FLASH irradiation depletes oxygen within water for different radiation types such as photons, protons and carbon ions.
Methods: This study presents measurements of the oxygen consumption in sealed, 3D printed water phantoms during irradiation with X-rays, protons and carbon ions at varying dose rates up to 340 Gy/s. The oxygen measurement was performed using an optical sensor allowing for non-invasive measurements.
Results: Oxygen consumption in water only depends on dose, dose rate and linear energy transfer (LET) of the irradiation. The total amount of oxygen depleted per 10 Gy was found to be 0.04 - 0.18 % atm for 225 kV photons, 0.04 - 0.25 % atm for 224 MeV protons and 0.09 - 0.17 % atm for carbon ions. consumption depends on dose rate by an inverse power law and saturates for higher dose rates because of self-interactions of radicals. Higher dose rates yield lower oxygen consumption. No total depletion of oxygen was found for clinical doses.
Conclusions: FLASH irradiation does consume oxygen, but not enough to deplete all the oxygen present. For higher dose rates, less oxygen was consumed than at standard radiotherapy dose rates. No total depletion was found for any of the analyzed radiation types for 10 Gy dose delivery using FLASH.
Comments: 23 pages, 7 figures
лошадь, диаграмма, Фейнман

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