Dosimetry of brachytherapy using radioactive nanoparticles: in silico

• Autor(a) principal: Baljeet Seniwal
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/36710; https://orcid.org/0000-0001-8250-5982
• topic: LDR brachytherapy; Radioactive nanoparticles; Dose point kernels; Monte Carlo methods; Engenharia nuclear; Braquiterapia; Método de Monte Carlo

Radioactive nanoparticles (radio-NPs) functionalized with tumor specific biomolecules, injected intratumorally, have been reported as an alternative to low dose rate (LDR) seed based brachytherapy (BT). In radiation based cancer treatments accurate estimation of absorbed dose is crucial for proper disease control and to minimize the risk of radiation induced side effects. Currently, used Medical Internal Radiation Dose (MIRD) formalism for internal dosimetry purposes do not consider the impact of uptake and washout of radiopharmaceutical on the cell survival fraction (SF) and absorbed dose estimation. The single cell dosimetry (SCD), based on MIRD formalism, is generally used to evaluate the dosimetric characteristics of radionuclides for theranostic applications. However, there exists discrepancies in the graphical methods and radial energy distribution, used to estimate the dose distribution. Moreover, precise modeling of radiation transport in the medium by Monte Carlo (MC) codes plays a pivotal role in the estimation of absorbed dose. The dose point kernel (DPK) are used to: (i) test the accuracy of different Monte Carlo (MC) codes, by performing comparison in terms of DPK; and (ii) estimate 3D-absorbed dose in nuclear medicine. However, as per our knowledge the impact differences in DPK on absorbed dose was not investigated. This PhD project aims to perform dosimetry of LDR BT applications, using radio-NPs, and fill the above mentioned gaps in literature using MC methods. The dosimetric calculations were performed using two widely used MC codes: Geant4-DNA and EGSnrc. Initially, the comparison in terms of DPK for electrons in energy range of 1 keV to 3 MeV was made to test the accuracy of both codes. After validation, SCD approach was used to evaluate the dosimetric characteristics of 12 alpha/beta/auger emitting radionuclides for theranostic applications. The concept of radial dose function was also proposed for graphical representation of dose distribution. Further, the cell survival curves published in literature were replicated using the mathematical model proposed by Sefl et al. 2016. Our findings show that, both Geant4-DNA and EGSnrc can accurately simulate the transport of low energy electrons with respect to other MC codes. Moreover, the largest differences between DPKs were found for electron energies below 10 keV, which resulted in inhomogeneous dose distribution in micrometer and no impact on millimeter sized voxels. The alpha emitters were found to deposit highest absorbed dose in comparison to auger and beta emitters. Furthermore, we effectively replicated the cell survival curves published in literature on the use of radio-NPs for LDR BT applications. It was concluded that the accuracy of the MC codes and MC parameters must be validated and benchmarked before using them for dosimetry purposes. Also, the accurate knowledge of uptake rate, washout rate of NPs, radio-sensitivity and tumour repopulation rate is important for the calculation of cell survival curves.