4 th International Conference on Automation, Control Engineering and Computer Science (ACECS - 2017) Proceedings of Engineering and Technology – PET Vol.19, pp.104-110 Copyright IPCO-2017 ISSN 2356-5608 Modeling of a Linear Accelerator Saturne 43 and Study of Photon Dose Distributions A.ZEGHARI*, R.SAAIDI, M.MGHAR, R. CHERKAOUI EL MOURSLY Laboratory of Nuclear Physics, Faculty of Sciences, , Mohammed V University, Rabat, Morocco krmzeghari@gmail.com Abstract— BEAMnrc is a widely used Monte Carlo (MC) code for simulation of photon and electron transport in the radiotherapy area. The aim of this study was to ameliorate a technique that changing the initial properties of incident electron beam as purpose to have the difference between calculated and measured values of doses produced by the linear accelerator (linac) Saturne 43 machine to be within 1.5%/1mm. We changed the initial electron energy and full width half maximum (FWHM) of the radius of the electron beam incident on the tungsten target to find the percentage depth dose(PDD), dose profile(DP) curves, the tissue-phantom ratio TPR 20/10 , the energy fluence distribution and angular distribution for a square field size 10×10 cm 2 . The value of TPR 20/10 agrees well with the publisher related works, also we could find quantitatively good results which agree well with experimental PDD and lateral profiles at 10 cm depth. Moreover, we could reduce the discrepancy between measured and calculated data photon dose distributions to be within 1.5%/1mm in the gamma index method for the energy 11.8 MeV and FWHM= 0.07 cm. Using BEAMnrc code on modeling and simulation of the treatment head of the Saturne 43 machine was successfully done altering the initial properties of electron source. That shows the efficacy and accuracy of the technique used in this paper to obtain the discrepancy within 1.5%/1 mm. Keywords— Monte Carlo; photon dose distribution; BEAMnrc; Tissue-Phantom Ratio I. INTRODUCTION Cancer is the principal cause of death globally. The International Agency for Research on Cancer (IARC) recently estimated that 7.6 million deaths worldwide were due to cancer with 12.7 million new cases per year being reported worldwide. External beam radiation is delivered by aiming high-energy rays (photons) to the position of the tumour to destroy cancer cells. The evolution of external radiotherapy techniques allows an improvement in the development of the treatment plan. This stage consists in defining in a sophisticated way all the irradiations that will have to be applied to the patient in order to completely destroy his tumour, made up of cancer cells. Clinical application of such techniques requires reliable estimation of the absorbed dose distributions to sufficiently irradiate the cancerous tissue. Patient dosimetry then becomes the stage where treatment planning can be calculated, evaluated, verified experimentally and finally validated. Monte Carlo techniques are the reference tool for precise dose calculations and their accuracy has been fully quantified in the literature. Researchers and clinicians used the MC simulations to test the accuracy of the computation dose for the treatment planning systems (TPS) in the simple geometry. In the last years, MC techniques can be used in the dosimetry and TPS using the last development of computer technology. Photon beams parameters generated by linacs show differences between manufacturers and may be seen also by the same manufacturer. There have been many works of MC techniques in the simulation of the linacs machine (Varian, Elekta, Siemens, Philips…) defining the influence of multi levelled equations, graphics, and tables are not prescribed, initial electron beam parameters for radiotherapy photon beams. Verhaegen and Seuntjens [1] used the mean energy of 6 MeV and the FWHM electron spot of 0.2 cm. Sheikh-Baghri and Rogers [2] simulated the Siemens KD, Varian Clinac, and Elekta SL25, they altered the energy in steps of 0.1 MeV over a range from 5.5 to 6.6 MeV and varied the radius from