Monte Carlo simulation of dose distributions from a synchrotron-produced microplanar beam array using the EGS4 code system⁴

Abstract

Microbeam therapy is established as a general concept for brain tumour treatment. A synchrotron based x-ray source was chosen for experimental research into microbeam therapy, and therefore new simulations were essential for investigating the therapy parameters with a proper description of the synchrotron radiation characteristics. To design therapy parameters for tumour treatments, the newly upgraded LSCAT (Low energy SCATtering) package of the EGS4 Monte Carlo simulation code was adapted to develop an accurate self-written user code for calculating microbeam radiation dose profiles with a precision of 1 microm. LSCAT is highly suited to this purpose due to its ability to simulate low-energy x-ray transport with detailed photon interactions (including bound electron incoherent scattering functions, and linear polarized coherent scattering). The properties of the synchrotron x-ray microbeam, including its polarization, source spectrum and beam penumbra, were simulated by the new user codes. Two concentric spheres, an inner sphere, defined as a brain, and a surrounding sphere, defined as a skull, represented the phantom. The microbeam simulation was tested using a 3 x 3 cm array beam for small treatment areas and a 6 x 6 cm array for larger ones, with different therapy parameters, such as beam width and spacing. The results showed that the microbeam array retained an adequate peak-to-valley ratio, of five times at least, at tissue depths suitable for radiation therapy. Dose measurements taken at 1 microm resolution with an 'edge-on' MOSFET validated the basics of the user code for microplanar radiation therapy.

Interlaced x-ray microplanar beams: A radiosurgery approach with clinical potential

“…This version included such details as the beam's linear polarization (27,28). The work followed similar calculations made earlier (18,19,21).…”

“…Compton scattering and photoelectric events that set electrons in motion produce the dose, and Monte Carlo simulations are used to calculate the MRT dose distributions (18)(19)(20)(21).…”

MOSFET dosimetry for microbeam radiation therapy at the European Synchrotron Radiation Facility

“…Most of the theoretical calculations using Monte Carlo codes 8,9 have predicted the dose distribution around one single microbeam in the radial direction for very small voxel sizes like 1 m cube. These calculations must be performed for distances from the microbeam peak extending perpen-dicular about 25 millimeters outwards, since the actual valley dose is calculated by overlapping the tails of the microbeams.…”

“…There are several reports on Monte Carlo based computational MRT microdosimetry 8,9 that quantify the dependence of doses in the peaks and valleys in an H 2 O filled phantom on parameters that include beam photon energy spectrum, size and number of microbeams, dimensions of the phantom, microbeam spacing, position of microbeams, and depth of the point of interest from the phantom surface. Our MOSFET results are compared with computations using the PSI version of the GEANT Monte Carlo photon-electron transport code, 10 into which the photon and electron cross section and atomic data compiled at Lawrence Livermore National Laboratory in the 1990s have been incorporated ͑the Evaluated Photon Data Library, EPDL, 11,12 the Evaluated Electron Data Library EEDL, 13 and the Evaluated Atomic Data Library EADL 14 ͒.…”

Use of MOSFET dosimeters to validate Monte Carlo radiation treatment calculation in an anthropomorphic phantom

“…In 2003, [4] the author demonstrated a good match for the MOSFET measures and MC calculated dose by electron beams in radiotherapy. Three years before, I. Orion [5] measurements with MOSFET validated the basics of the EGS4code for synchrotron-produced microplanar for radiation therapy. This paper goes a step further in this research field, including a full detailed model of LinAc head irradiation, and the customized model of the patient geometry.…”