A virtual source model recently developed for external radiotherapy,
which includes two photon sources and two electron sources, is tested for stereotactic
radiosurgery with a dynamic micro-multileaf collimator. A 6 MV Elekta Precise
linac that incorporates a 3Dline L’Arancio dynamic micro-multileaf collimator was
considered. The capabilities of the virtual source model have been tested against
full simulations performed with the Monte Carlo simulation code PENELOPE using
both PENELOPE itself and the rapid Monte Carlo code DPM. The reference
10 cm × 10 cm radiation field as well as small fields of 1.2 cm × 1.2 cm, 2.9 cm × 2.9 cm
and 5.8 cm×5.8 cm were considered. The dynamic micro-multileaf collimator effect can
be included in the virtual source model by reducing the width of the photon primary
source by a factor 3. In all cases the virtual source model simulations were in very
good agreement with the complete ones including the linac and collimator geometries.
