Table 4.

Off‐axis‐ratio for selected field sizes measured at different depths (D) and 90 cm SSD.

Field Size (cm2)	Energy	$D=D_{\mathit{\text{max}}}$	$D=5\hspace{0.17em}\mathit{\text{cm}}$	$D=10\hspace{0.17em}\mathit{\text{cm}}$	$D=20\hspace{0.17em}\mathit{\text{cm}}$
$2\times 2$	10 MV	0.858	0.861	0.872	0.879
	10MVFFF	0.915	0.913	0.912	0.912
$4\times 4$	10 MV	0.970	0.966	0.963	0.964
	10MVFFF	0.947	0.943	0.941	0.943
$10\times 10$	10 MV	0.986	0.973	0.958	0.942
	10MVFFF	0.827	0.818	0.808	0.803
$15\times 15$	10 MV	1.007	0.990	0.973	0.944
	10MVFFF	0.748	0.741	0.730	0.721
$20\times 20$	10 MV	1.011	1.004	0.981	0.946
	10MVFFF	0.669	0.664	0.656	0.647
$25\times 25$	10 MV	1.020	1.014	0.992	0.947
	10MVFFF	0.607	0.602	0.595	0.582
$30\times 30$	10 MV	1.042	1.029	1.006	0.951
	10MVFFF	0.550	0.545	0.542	0.533
$35\times 35$	10 MV	1.047	1.034	1.007	0.951
	10MVFFF	0.502	0.497	0.489	0.486
$40\times 40$	10 MV	1.049	1.034	1.007	0.952
	10MVFFF	0.459	0.456	0.452	0.443