Browsing by Author "Moskvin, Vadim"

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    Challenges of dosimetry of ultra-short pulsed very high energy electron beams
    (Elsevier, 2017-10-01) Subiel, Anna; Moskvin, Vadim; Welsh, Gregor H.; Cipiccia, Silvia; Reboredo, David; DesRosiers, Colleen; Jaroszynski, Dino A.; Radiation Oncology, School of Medicine
    Very high energy electrons (VHEE) in the range from 100 to 250MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetric properties compared with 6–20MV photons generated by clinical linear accelerators (LINACs). VHEE beams have characteristics unlike any other beams currently used for radiotherapy: femtosecond to picosecond duration electron bunches, which leads to very high dose per pulse, and energies that exceed that currently used in clinical applications. Dosimetry with conventional online detectors, such as ionization chambers or diodes, is a challenge due to non-negligible ion recombination effects taking place in the sensitive volumes of these detectors. FLUKA and Geant4 Monte Carlo (MC) codes have been employed to study the temporal and spectral evolution of ultrashort VHEE beams in a water phantom. These results are complemented by ion recombination measurements employing an IBA CC04 ionization chamber for a 165MeV VHEE beam. For comparison, ion recombination has also been measured using the same chamber with a conventional 20MeV electron beam. This work demonstrates that the IBA CC04 ionization chamber exhibits significant ion recombination and is therefore not suitable for dosimetry of ultrashort pulsed VHEE beams applying conventional correction factors. Further study is required to investigate the applicability of ion chambers in VHEE dosimetry.
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    A semi-empirical model for the therapeutic range shift estimation caused by inhomogeneities in proton beam therapy
    (American Association of Physicists in Medicine, 2012-03-08) Moskvin, Vadim; Cheng, Chee-Wai; Fanelli, Leia; Zhao, Li; Das, Indra J.; Radiation Oncology, School of Medicine
    The purpose of this study was to devise a simple semi-empirical model to estimate the range shift in clinical practices with high-Z inhomogeneity in proton beam. A semi-empirical model utilizing the logarithmic dependence on Z in stopping power from Bohr's classical approach has been developed to calculate the range shift due to the presence of inhomogeneity. Range shift from metallic plates of atomic number Z of various thicknesses were measured in water using a parallel plate ionization chamber and calculated with the FLUKA Monte Carlo code. The proton range shifts for bone and polymethyl methacrylate (PMMA) were estimated using the semi-empirical model and compared with Monte Carlo calculation. The semi-empirical equation to determine range shift and water equivalent thickness is presented. The model predicts a shift of the therapeutic range to within 2.5% accuracy for initial proton energies of 50 to 250 MeV and atomic numbers from 3.3 (effective Z for water) to 82. This equation is independent of beam energy, and thus provides range shift from high-Z materials without the knowledge of proton energy. The proposed method of calculating the therapeutic range shift accurately requires only knowledge of the effective or actual atomic number of the inhomogeneity and the thickness of the inhomogeneity along the beam direction. The model generalizes the range shift calculation for any material based on its effective atomic number, and permits reliable prediction of the range shift for material combinations where no data is currently available. The proposed model can be readily implemented in routine clinical practice for proton range shift estimation and quality assurance on the treatment planning.
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    Very High Energy Electron Laser Plasma Accelerators for use in Radiotherapy
    (Office of the Vice Chancellor for Research, 2010-04-09) DesRosiers, Colleen; Moskvin, Vadim; Stewart, Keith
    Very high energy electron beams, greater than 150 MeV, have been shown to have potential benefit in radiotherapy applications. Laser plasma technology is a highly efficient electron accelerator and this technology may be used to design an optimal radiotherapy accelerator.