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In (a)–(c) the horizontal calibration factor, C(x), is plotted for a 4 × 4, 10 × 10, and 20 × 20 cm2 6 MV beam at imaging distances of L = 45, 100, and 150 cm. In (b) the vertical calibration factor, C(z), for all three field sizes at each imaging distance is plotted.
