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WE‐C‐AUD‐04: Monte Carlo Simulations of Air Cavities in Phantoms Submerged in Magnetic Fields
Author(s) -
Yanez R,
Dempsey J F
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2761511
Subject(s) - monte carlo method , electron , magnetic field , magnetic resonance imaging , materials science , dosimetry , absorbed dose , radiation treatment planning , radiation , computational physics , medical imaging , radius , radiation therapy , physics , nuclear medicine , optics , computer science , radiology , nuclear physics , medicine , computer security , statistics , mathematics , quantum mechanics
Purpose: We present studies in support of the development of a magnetic resonance imaging (MRI) guided intensity modulated radiation therapy (IMRT) device for the treatment of cancer patients. Fast and accurate computation of the absorbed ionizing radiation dose delivered in the presence of the MRI magnetic field are required for clinical implementation. Method and Materials: The fast Monte Carlo simulation code DPM, optimized for radiotherapy treatment planning, is modified to simulate electron transport in uniform, static magnetic fields. Results: Simulations of dose deposition in inhomogeneous phantoms in which a layer of air is sandwiched in water shows that a lower MRI field strength is to prefer in order to avoid dose build‐up, due to returning electrons, in tissue surfaces. For a magnetic field of 0.3 T, cavities of up to several millimeters in thickness are safe from build‐ups. Larger cavities require the use of opposing beams to cancel out the effect of returning electrons. Conclusions: The effect of a B=0.3 T magnetic field in the dose deposition by a Co‐60 source is only appreciable in large air cavities, where a dose build‐up due to returning electrons is formed near material boundaries. Cavities with dimensions smaller than the gyration radius are not severely affected by dose build‐ups. For B=0.3 T cavities of the order of several millimeters are safe from dose build‐ups. Research sponsored by ViewRay Incorporated.