Physics study of microbeam radiation therapy with PSI-version of Monte Carlo code GEANT as a new computational tool.
Microbeam radiation therapy (MRT) is a currently experimental method of radiotherapy which is mediated by an array of parallel microbeams of synchrotron-wiggler-generated x-rays. Suitably selected, nominally supralethal doses of x-rays delivered to parallel microslices of tumor-bearing tissues in rats can be either palliative or curative while causing little or no serious damage to contiguous normal tissues. Although the pathogenesis of MRT-mediated tumor regression is not understood, as in all radiotherapy such understanding will be based ultimately on our understanding of the relationships among the following three factors: (1) microdosimetry, (2) damage to normal tissues, and (3) therapeutic efficacy. Although physical microdosimetry is feasible, published information on MRT microdosimetry to date is computational. This report describes Monte Carlo-based computational MRT microdosimetry using photon and/or electron scattering and photoionization cross-section data in the 1 eV through 100 GeV range distributed publicly by the U.S. Lawrence Livermore National Laboratory (LLNL) in the 1990s. These are compared with Monte Carlo-based microdosimetric computations using a code and physical data available in the 1980s. With the aim of using the PSI-version of GEANT Monte Carlo code for future macro- and micro/nano-dosimetric studies of Microbeam Radiation Therapy (MRT) a comparison of this code is made with the INHOM(EGS4) (version 1990), Dilmanian-CPE and Persliden-CPE Monte Carlo photon-electron codes (both version 1990) with which the absorbed dose distributions were calculated in 1990 and 1991 considering, (a) a single cylindrical microbeam, (b) multiple cylindrical microbeams in an orthogonal square bundle, and (c) multiple planar microbeams. It is shown that the PSI-version of GEANT can potentially deliver more accurate results (a) using presently the most advanced atomic data, and especially (b) employing "Single-collision" electron transport instead of only the "Condensed-history" electron transport as in code INHOM(EGS4). In contrast Dilmanian-CPE and Persliden-CPE codes deposit the electron energy locally instead of transporting it to the correct position.
Stepanek
J
J
Institute of Pathology, University of Bern, Switzerland. stepanek@psi.ch
Blattmann
H
H
Laissue
J A
JA
Lyubimova
N
N
Di Michiel
M
M
Slatkin
D N
DN
D000465:Algorithms; D002244:Carbon; D004307:Dose-Response Relationship, Radiation; D004579:Electron Transport; D004583:Electrons / Q000627:therapeutic use; D006801:Humans; D006859:Hydrogen; D007477:Ions; D009010:Monte Carlo Method; D009374:Neoplasms, Experimental / Q000532:radiotherapy; D009584:Nitrogen; D010100:Oxygen; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011874:Radiometry / Q000379:methods; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation; D012984:Software; D014867:Water; D014965:X-Rays
D007477:Ions; D014867:Water; D002244:Carbon; D006859:Hydrogen; D009584:Nitrogen; D010100:Oxygen