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Figure 3: Comparisons between calculated and measured PDD at points between 1 and 5 cm distance from the air/solidwater interface in phantoms A (2cm air gap), B (4cm air gap), and C (6cm air gap), (from left to right) for field sizes 3 × 3, 5 × 5, and 10 × 10 cm2 (from top to bottom). The Ä (%) was calculated using Equation 1. (6 MV photon beam, 100 cm SSD, 100 MUs).Abbreviations: AAA = Anisotropic Analytical Algorithm, AXB = Acuros XB Algorithm, PDD = Percent Depth Dose, Ä (%) = Dose Difference, SSD = Source to Surface Distance, MUs = Monitor Units. 
