Canan KÖKSAL AKBAŞ, Nazmiye DÖNMEZ KESEN

The Investigation of The Anisotropic Analytical Algorithm (AAA) and the Acuros XB (AXB) Dose Calculation Algorithms Accuracy in Surface and Buildup Region for 6 MV Photon Beam Using Gafchromic EBT3 Film

OBJECTIVE Due to the complexity of build-up region dosimetry, treatment planning system (TPS) calculations may present significant inaccuracy in surface and buildup regions. The main aim of the current study was to investigate the calculated build-up and surface doses for 6 MV photon beams by Eclipse TPS version 15.1 Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB) algorithm. METHODS Calculations were compared to surface doses measured by Markus parallel-plate ionization chamber which is admitted asan alternative to the extrapolation chambers to obtain the most accurate results for surface region and by Gafchromic EBT3 film which is frequently preferred in in vivo dosimetry (IVD) applications for skin dose measurements because of their practical usage. The measurements were made for 5×5, 10×10, and 20×20 cm2 field sizes at the surface and in the buildup region of 6 MV. Dosimetry systems were placed in a water equivalent solid phantom; all measurements were performed at 100 cm source-detector distance. RESULTS The surface doses using 6 MV photon beams for 5×5, 10×10, and 20×20 cm2 field sizes at 0.07 mm was found to be 14.00% and 12.79%; 19.69% and 18.80%; and 30.87% and 27.07% for Markus chamber and Gafchromic EBT3 film, respectively. CONCLUSION In clinics, to be sure of the correctness of surface and buildup region dose calculation, QA procedures must be performed for all algorithms implanted in TPS before using them for patient treatment planning. Since it exhibits the similar results by Markus parallel plate ion chamber in the surface and buildup region, Gafchromic EBT3 film can be a preferable dosimeter in IVD.

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