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Example 1: Source modelling in Elekta Oncentra
Source modelling is part of the calculation of direct photon energy fluence (the
energy fluence of non-scattered photons reaching the patient which calculated
on a 1mm matrix resolution).
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Beam source of finite size
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Source intensity distribution model:
2D Gaussian
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Source intensity distribution parameters:
Determined individually for each machine
and beam energy using measured data (fitting measured profiles and small field output
factors)
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Source distribution is discretised on a 2D grid; amplitudes on each position
renormalized to sum up to unity
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The resolution of this grid depends on its size, the resolution of the energy fluence
matrix and the distance to the collimators; derived at runtime
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Geometric penumbra modelled by
accounting for shape of collimator/MLC edge and its
position with respect to the source
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For collapsed code dose calculation: The effect of the finite source is considered
by convolving the projected source distribution with a constant energy fluence
bounded by the actual field shape. The method takes into account the position
of the collimating element from the beam axis accounting of the distance of the
collimating device from the source.
Manual: Physics and Algorithms v4.3
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