Study on Dose Deposited Characteristics of Small-Field X-Ray Beam from Accelerator in Heterogeneous Phantom Under Magnetic Field
Objective To investigate the dose deposited characteristics of small-field X-ray beam generated by accelerator in heterogeneous phantom under magnetic field using Monte Carlo simulation method.Methods A TrueBeam 6 MV head model was constructed using EGSnrc combined with phase space file provided by Varian's official.Simulations were performed at a source-to-skin distance of 100 cm for both a routine-field of 10 cm×10 cm and a small-field of 2 cm×2 cm.First,the energy deposition of the routine-field was simulated in homogeneous water phantom to validate the model's accuracy.Then,the energy deposition of the small-field was simulated in heterogeneous water-lung-water and water-bone-water phantoms.A 1.5 T static magnetic field orthogonal to the beam direction was added to the spatial setup before conducting the simulations.Finally,the dose deposition characteristics were analyzed.Results The results for the routine-field showed that without a magnetic field,the depth of Dmax was 1.5 cm;the built-up area was shortened and the depth of Dmax shifted forward to 1.1 cm in the presence of magnetic field.The results for the small-field showed that the presence of magnetic field would lead to a reversal in the dose deposited characteristics.There was a dose change of 36.92%and-36.44%at the two interface regions in the water-lung-water phantom,and there was a dose change of-11.17%and 10.89%at the two interface regions in the water-bone-water phantom.Conclusion The presence of magnetic field can cause significant changes in the dose deposition of the small-field beam generated by the accelerator within the phantom,especially at the junction of heterogeneous mediums.
Monte Carlo simulationmagnetic fieldsmall-field beamheterogeneous phantomdose deposited characteristic
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