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Investigation of Ocular Tumor Dose Enhancement in Proton Therapy in the Presence of Nanoparticles of Different Materials

Alamgir, Jafar | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56346 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Hosseini, Abolfazl; Salimi, Ehsan
  7. Abstract:
  8. In recent years, the effect of the presence of nanoparticles in the tumor in order to increase the benefit of the treatment in radiation therapy has been the focus of many researchers. Although for photon irradiation, a significant dose increase due to the presence of nanoparticles has been observed, in the case of proton irradiation, due to the different nature of the beam and the lower cross-section of protons with metals compared to photons, scattered and in some cases contradictory findings have been published in the articles, and more studies are needed in this field. Due to laboratory limitations, Monte Carlo simulation is an appropriate tool for simulating difficult real-world situations. This research has implemented a comprehensive study on the effect of nanoparticles on dosimetry parameters in proton therapy of eye tumors in three stages: 1-The first stage (in macroscopic scale): realistic definition of nanoparticles in the eye tumor volume placed in a head phantom along with simulation of a therapeutic accelerator; 2-The second stage (in microscopic scale): defining a single nanoparticle in the water medium in order to more accurately examine the secondary particles emitted from the nanoparticle’s surface, and to plot the radial dose distribution and the dose enhancement factor; 3-The third stage (in microscopic scale): defining a human cell model in order to calculate the dose and direct and indirect DNA damages with and without the presence of nanoparticles in the cell. All the above stages were repeated for gold, hafnium and gadolinium nanoparticles. The proton energy in the first stage was 62.8 MeV, and in the second and third stages, it was considered selectively from 5 to 150 MeV. Also, two different physical interaction models (Livermore and Penelope) were compared. The results showed that the difference between the two physical models in the production of secondary particles was often less than 10%, although in some cases it reached up to 30%. In the case of a single nanoparticle, the dose enhancement factor around the gold nanoparticle was 14 times, which is the highest value compared to hafnium and gadolinium nanoparticles, which were 10 and 6 times, respectively. This drastic increase in dose is achieved due to the excessive increase of proton interactions with the metal in the microscopic scale. The results of the third stage, in which the ability to define the concentration of nanoparticles is also available and this is closer to the real conditions, show that except for very high concentrations (which are not clinically achievable), a significant dose increase due to the presence of nanoparticles in proton therapy was not observed, which is consistent with the results published in the articles. Therefore, it can be concluded that, from the point of view of simulation, the use of metal nanoparticles in proton therapy of eye tumor will not have a noticeable effect on the dosimetry parameters due to the limitation in the concentration of nanoparticle injection. In the end, some suggestions are given for the continuation of this study
  9. Keywords:
  10. Proton Therapy ; DNA Damage ; GEANT4 Toolkit ; Nanoparticles ; Eye Tumor

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