Table 2.

The RPC‐measured and institution treatment planning system‐calculated small field size dependence output factor values for Elekta machines. The values in square brackets and parentheses beneath each energy for each field size value are the average absolute percent differences and standard deviations of the values, respectively. For each energy and field size, the number of measurements (accelerators) is also shown.

	Elekta 6 MV		Elekta 10 MV		Elekta 18 MV
Field Size (cm x cm)	RPC	Institution	RPC	Institution	RPC	Institution
$10\times 10$	1.000	1.000	1.000	1.000	1.000	1.000
$6\times 6$	0.930	0.934	0.937	0.940	0.945	0.947
	(0.010)	(0.009)	(0.004)	(0.005)	(0.002)	(0.003)
	[0.5%]		[0.7%]		[0.3%]
	$(\mathrm{n}=18)$		$(\mathrm{n}=6)$		$(\mathrm{n}=5)$
$4\times 4$	0.878	0.888	0.890	0.891	0.901	0.918
	(0.015)	(0.027)	(0.009)	(0.010)	(0.002)	(0.039)
	[1.3%]		[0.6%]		[0.4%]
	$(\mathrm{n}=22)$		$(\mathrm{n}=8)$		$(\mathrm{n}=6)$
$3\times 3$	0.842	0.848	0.857	0.862	0.861	0.863
	(0.012)	(0.009)	(0.003)	(0.005)	(0.003)	(0.004)
	[0.9%]		[0.6%]		[0.6%]
	$(\mathrm{n}=17)$		$(\mathrm{n}=6)$		$(\mathrm{n}=4)$
$2\times 2$	0.790	0.796	0.796	0.802	0.786	0.798
	(0.007)	(0.010)	(0.009)	(0.008)	(0.006)	(0.019)
	[1.6%]		[1.3%]		[2.4%]
	$(\mathrm{n}=17)$		$(\mathrm{n}=6)$		$(\mathrm{n}=4)$