Highlights
- •Developing an MC-based analytical model reproducing stray neutrons in proton therapy.
- •Upgrading the literature model to enable full 3D H*(10) neutron mapping.
- •Limited efficiency of the literature model in a clinically-relevant configuration.
- •Upgrades given to model neutron variation with beam collimation and modulation.
- •MC-based analytical model consolidated with experimental measurements.
Abstract
Purpose
This study focuses on the configuration and validation of an analytical model predicting
leakage neutron doses in proton therapy.
Methods
Using Monte Carlo (MC) calculations, a facility-specific analytical model was built
to reproduce out-of-field neutron doses while separately accounting for the contribution
of intra-nuclear cascade, evaporation, epithermal and thermal neutrons. This model
was first trained to reproduce in-water neutron absorbed doses and in-air neutron
ambient dose equivalents, H*(10), calculated using MCNPX. Its capacity in predicting out-of-field doses at any
position not involved in the training phase was also checked. The model was next expanded
to enable a full 3D mapping of H*(10) inside the treatment room, tested in a clinically relevant configuration and
finally consolidated with experimental measurements.
Results
Following the literature approach, the work first proved that it is possible to build
a facility-specific analytical model that efficiently reproduces in-water neutron
doses and in-air H*(10) values with a maximum difference less than 25%. In addition, the analytical
model succeeded in predicting out-of-field neutron doses in the lateral and vertical
direction. Testing the analytical model in clinical configurations proved the need
to separate the contribution of internal and external neutrons. The impact of modulation
width on stray neutrons was found to be easily adjustable while beam collimation remains
a challenging issue. Finally, the model performance agreed with experimental measurements
with satisfactory results considering measurement and simulation uncertainties.
Conclusion
Analytical models represent a promising solution that substitutes for time-consuming
MC calculations when assessing doses to healthy organs.
Keywords
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Article info
Publication history
Published online: February 12, 2015
Accepted:
January 26,
2015
Received in revised form:
January 22,
2015
Received:
December 10,
2014
Identification
Copyright
© 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.
