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On pathlength and energy straggling of megavoltage electrons slowing down

      Abstract

      Purpose

      to elucidate the effects of multiple scattering and energy-loss straggling on electron beams slowing down in materials.

      Methods

      EGSnrc Monte Carlo simulations are done using a purpose-written user-code.

      Results

      Plots are presented of the primary electron’s energy as a function of pathlength for 20 MeV electrons incident on water and tantalum as are plots of the overall distribution of pathlengths as the 20 MeV electrons slow down under various Monte Carlo scenarios in water and tantalum. The distributions range from 1 % to 135 % of the CSDA range in water and from 1 % to 186 % in tantalum. The effects of energy-loss straggling on energy spectra at depth and electron fluence at depth are also presented.

      Conclusions

      The role of energy-loss straggling and multiple scattering are shown to play a significant role in the range straggling which determines the dose fall-off region in electron beam dose vs depth curves and a significant role in the energy distributions as a function of depth.

      Keywords

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        Accurate condensed history Monte Carlo simulation of electron transport. I. EGSnrc, the new EGS4 version.
        Med Phys. 2000; 27: 485-498
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