Bahreyni Toosi, M. T. and Momen Nezhad, M. and Saberi, H. and Bahreyni Toosi, M. H. and Hashemian, A. and Salek, R. and Miri, H. (2005) A Monte Carlo Simulation of Photon Beam Generated by a Linear Accelerator. Iranian Journal of Medical Physics, 2 (2). pp. 312.

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Abstract
ntroduction: Â Monte Â Carlo Â simulation Â is Â the Â most Â accurate Â method Â of Â simulating Â radiation Â transport Â andÂ predicting doses at different points of interest in radiotherapy. A great advantage of the Monte Carlo methodÂ compared Â to Â the Â deterministic Â methods Â is Â the Â ability Â to Â deal Â accurately Â with Â any Â complex Â geometry. Â ItsÂ disadvantage is the extremely long computing time required to obtain a dose distribution with good statisticalÂ accuracy.Â Materials and Methods: The MCNP4C Monte Carlo code was used to simulate a 9 MV photon beam fromÂ a Neptun 10PC linear accelerator. The accelerator was modeled as a complete unit consisting of a target, exitÂ window, initial collimator, primary collimator, flattening filter, monitor chamber and secondary collimator.Â The geometrical details and the composition of each component was either obtained from the manufacturer orÂ was Â directly Â measured. Â The Â simulation Â of Â the Â source Â was Â performed Â in Â a Â two Â step Â process. Â Initially, Â theÂ electron source was defined. Secondly, the bremsstrahlung energy spectra and the fluence distribution at theÂ scoring Â planes Â were Â used Â to Â define Â the Â photon Â source. Â The Â simulated Â electron Â beam Â energy Â followed Â aÂ Gaussian distribution, with FWHM equal to 12 in nominal energy. The used intensity distribution of theÂ electron beam also followed a Gaussian distribution with a FWHM equal to 0.34 cm. To compute the photonÂ beam data a 50 Ã� 50 Ã� 40 cm 3 Â water phantom located at SSD = 100 cm was simulated. The depth dose andÂ the dose profile curves were calculated for four different field sizes (5Ã�5, 10Ã�10, 20Ã�20 and 30Ã�30 cm 2 ) andÂ compared against the measured values. The lowenergy cutoff for the photons and electrons was 10 and 500Â KeV, respectively. The measurements were carried out by using a Scanditronix dose scanning system and aÂ 0.12 cm 3 Â RK ionization chamber.Â Results: To verify the simulated model, the calculated Monte Carlo dose data were compared against theÂ corresponding measured values. The energy spectra and the angular distribution of the xray beam generatedÂ by the Neptun 10PC linac was examined. The result showed an efficiency of about 73 for the production ofÂ bermsstrahlung photon by the target. The agreement between the calculated and the measured depth dose andÂ the dose profile was generally better than 2 for all the fields.Â Discussion and Conclusion: The simulation of the Neptun 10PC linac performed in this work is capable ofÂ computing the depth dose data and the beam profiles in water phantom for all the predefined fields includingÂ 5Ã�5, 10Ã�10, 20Ã�20 and 30Ã�30 cm 2 . Therefore, it can be concluded that MCNP4C is a suitable tool for theÂ dose calculation in radiotherapy. The simulated linac machine and the resulting data can be used to predictÂ the dose distribution in all complex fields.Â
Item Type:  Article 

Subjects:  WN Radiology . Diagnostic Imaging 
Divisions:  Journals > Iranian J Medical Physics 
Depositing User:  ijmp ijmp 
Date Deposited:  21 Jan 2018 15:31 
Last Modified:  21 Jan 2018 15:31 
URI:  http://eprints.mums.ac.ir/id/eprint/8999 
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