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Beam Modifiers
Most of the calculation time of a MCTP system is spent in the
jaws and MLC (when tracking photons and electrons through
high-Z materials many particles are lost, so it requires a lots of
CPU time to obtain sufficient particles that manage to cross
these parts)
To avoid waste of CPU time on photons and electrons tracking
through MLC and other collimating devices approximations
are introduced
Chen et al (2000): MCDOSE Ray-tracing based method for
calculating transmission through MLC geometry (only
works with virtual source model)