Highlights
- •A general methodology for optimization of existing Phase Space files was developed.
- •A linear relationship between beam divergence and lateral profiles was obtained.
- •Optimization factors for particles’ energy and direction have been identified.
- •Remarkable improvement in the agreement among measured and simulated data observed.
- •Viable alternative in absence of geometric information and validated Phase Space.
Abstract
This work proposes a methodology to produce an optimized phase-space (PhSp) for the
Elekta Synergy linac by tuning the energy and direction of particles inside the 6-MV
Elekta Precise PhSp, provided by the International Atomic Energy Agency (IAEA), for
Monte Carlo (MC) simulations. First, the energies of the particles emerging from the
original PhSp were increased by different factors, producing new PhSps. Percentage
depth dose (PDD) profiles were simulated and compared to measured data from a Synergy
linac for 6-MV photon beam. This process was repeated until a minimum difference was
reached. Particles’ directions were then manipulated following identified correlations
to lateral profiles, resulting in two distinct perturbation factors based on inline
and crossline profiles. Both factors were merged into one single optimal factor. For
energy optimization, an increase of 0.32 MeV applied to all particles inside the original
PhSp, but to 0.511 MeV annihilation photons, provided the best results. The direction
optimization factor was the combination of the individual factors for inline (0.605%)
and crossline (0.051%). The agreement between measured and simulated profiles, when
using the optimized PhSp, improved considerably in comparison to simulations performed
with the original IAEA PhSp. For all fields and depths analyzed, the discrepancies
for PDD, inline and crossline profiles dropped from 11.2%, 15.7% and 27.5% to under
1.4%, 4.7% and 13.2%, respectively. The optimized PhSp should not replace the full
linac modelling, however it offers an alternative for MC dose calculations when neither
geometric details nor validated IAEA PhSp are available to the user.
Keywords
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Article info
Publication history
Published online: June 24, 2019
Accepted:
June 15,
2019
Received in revised form:
June 5,
2019
Received:
December 7,
2018
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
