A simple approach to study the performance of electron Monte Carlo algorithm in cancer treatment using medical Linear Accelerator
Publication Date : 24/11/2015
Radiation therapy is a cancer treatment technique using ionizing radiations. This is possible by a medical Linear Accelerator (LINAC) along with a Treatment Planning System (TPS). Most commercial TPS incorporates complex treatment planning algorithms. The electron Monte Carlo (eMC) dose calculation algorithm of the EclipseTM TPS is based upon Monte Carlo simulation of the LINAC head and modelling of the beam characteristics. In this study, a simple and direct dosimetric method is introduced to check the performance of this algorithm for clinical use. The eMC calculated values of different dosimetric quantities such as treatment monitor units (MU), output factors (O.F) and cutout factors are compared with the measured data for available applicators, energy and selected Source to Surface Distances (SSD). Measurements were performed in Varian clinac - iX LINAC using plastic water phantom and 0.13 cm3 ionization chamber. The cutouts, made up of an alloy cerrobend, were prepared in various sizes and shapes. Our results show that the eMC calculated relative O.F for all applicators at different SSDs agree with the measurement within 3%. A clinically acceptable variation of 3% is observed in the cutout factors for square cutouts with sizes of 4 x 4 cm2 or larger. The comparison of irregular clinical cutouts in low and high energy beams with nominal and extended SSDs, yields that Monte Carlo calculated MU matches with corrected MU within 4%. Our results indicate that eMC algorithm shows acceptable agreement with the measured data. The implemented new method of direct measurement successfully validates the eMC for clinical use. Keywords: Linear accelerator; electron Monte carlo (eMC); monitor units; electron cutout; out put factor.
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