Analysis of dosimetric characteristics of energy 6 MV with and without flattening filter photon beam generated by the varian true beam linac using kruskal wallis H test

Abstract

Author(s): Achir Sara*, Mohammed El Adnani Krabch and Mourad Trihi

The aim of this study is to assess the capacity of the beam-matching of the characteristics of the Flattened (FF) and Unflattened (FFF) photon beam of the 6 MV energy of the Varian TrueBeam linac located at the Achifaa Specialized Center in Casablanca (Morocco). The dosimetric parameters in this research such as Percentage Depth Dose (PDD), surface dose, beam profile, Output Factor (OF), Transmission Factor (TF) and Dosimetric Leaf Gap (DLG) are analyzed by a non-parametric Kruskal-wallis test in order to study their degree of independence and a coefficient of variation a descriptive statistical analysis to measure the difference between these measurements. We observed a similarity between the FFF and FF beam data for surface dose and the beam profile for large irradiation field sizes; the output factor for small to medium field sizes, it was noted that the maximum depth dose (dmax) and the DLG factor were less than 1 mm. But a slight disparity existed between the FFF beams compared to the FF beams for the surface dose which was higher for small fields, the dmax was 7% lower and closer to the surface, the average energy of the PDD was 5% lower; the TPR (20/10) phantom tissue ratio was 6% lower for the reference field size (10* 10 cm2). The energy spectra of the photons was smoother generally, profiles are sharper for medium to large field sizes, the penumbra width was smaller and 7% lower, the output factor was 2% lower for the selected fields, 5% lower for medium to large field sizes, transmission factor was reduced by 17%. Finally, the parameters were reproducible between both types of beam energy ×6 MV (FFF-FF) since the p-value> 5% and V.R <20%; except the DLG of the MLC was 24% lower for the same X6 MV energy.

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