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Monte Carlo calculations of an Elekta Precise SL-25 photon beam model

Published online by Cambridge University Press:  18 August 2015

Fátima Padilla-Cabal ,
Mailyn Pérez-Liva ,
Elier Lara ,
Rodolfo Alfonso  and
Neivy Lopez-Pino
Fátima Padilla-Cabal
Affiliation:
Nuclear Physics Department, Instituto Superior de Tecnologías y Ciencias Aplicadas, La Habana, Cuba
Mailyn Pérez-Liva*
Affiliation:
Grupo de Física Nuclear, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Madrid, Spain
Elier Lara
Affiliation:
Department of Radiotherapy, Instituto Nacional de Oncología y Radiobiología, La Habana, Cuba
Rodolfo Alfonso
Affiliation:
Nuclear Physics Department, Instituto Superior de Tecnologías y Ciencias Aplicadas, La Habana, Cuba
Neivy Lopez-Pino
Affiliation:
Nuclear Physics Department, Instituto Superior de Tecnologías y Ciencias Aplicadas, La Habana, Cuba
*
Correspondence to: Mailyn Pérez-Liva, Ave Complutense, S/N, Grupo de Física Nuclear, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain. Tel: +34 91 394 4484. Fax: +34 91 394 5193. E-mail: mailyn01@ucm.es
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Abstract

Background

Monte Carlo (MC) simulations have been used extensively for benchmarking photon dose calculations in modern radiotherapy using linear accelerators (linacs). Moreover, a major barrier to widespread clinical implementation of MC dose calculation is the difficulty in characterising the radiation source using data reported from manufacturers.

Purpose

This work aims to develop a generalised full MC histogram source model of an Elekta Precise SL-25 linac (electron exit window, target, flattening filter, monitor chambers and collimators) for 6 MV photon beams used in standard therapies. The inclusion of many different probability processes such as scatter, nuclear reactions, decay, capture cross-sections and more led to more realistic dose calculations in treatment planning and quality assurance.

Materials and methods

Two different codes, MCNPX 2·6 and EGSr-BEAM, were used for the calculation of particle transport, first in the geometry of the internal/external accelerator source, and then followed by tracking the transport and energy deposition in phantom-equivalent tissues. A full phase space file was scored directly above the upper multilayer collimator’s jaws to derive the beam characteristics such as planar fluence, angular distribution and energy spectrum. To check the quality of the generated photon beam, its depth dose curves and cross-beam profiles were calculated and compared with measured data.

Results

In-field dose distributions calculated using the accelerator models were tuned to match measurement data with preliminary calculations performed using the accelerator information provided by the manufacturer. Field sizes of 3×3, 5×5, 10×10, 15×15 and 20×20 cm2 were analysed. Local differences between calculated and measured curve doses beneath 2% were obtained for all the studied field sizes. Higher discrepancies were obtained in the air–water interface, where measurements of dose distributions with the ionisation chamber need to be shifted for the effective point of measurement.

Conclusion

The agreements between MC-calculated and measured dose distributions were excellent for both codes, showing the strength and stability of the proposed model. Beam reconstruction methods as direct input to dose-calculation codes using the recorded histograms can be implemented for more accurate patient dose estimation.

Keywords

Elekta-linacMonte Carlo (MC) simulationsphoton beam model
Type
Technical Note
Information
Journal of Radiotherapy in Practice , Volume 14 , Issue 3 , September 2015 , pp. 311 - 322
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Copyright
© Cambridge University Press 2015 

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