Table 2.

Surface dose (D_s) values (%) in the presence of air gaps under different thicknesses of gel bolus and water surface of radiation field analyzer-300, obtained from central axis depth dose curve of 6 MV clinical photon beam for different field sizes

Bolus thickness (cm)	Field size (cm2)	Air gap (cm)					Reduction in “Ds”**
		0.0		1.0	2.0	3.0
No bolus	5 × 5	48.7	9.9*	-	-	-	-
	10 × 10	54.2	15.6*	-	-	-	-
	15 × 15	59.9	21.6*	-	-	-	-
	20 × 20	64.1	27.2*	-	-	-	-
	25 × 25	67.7	32.4*	-	-	-	-
0.5	5 × 5	92.0		87.0	83.6	77.2	14.8
	10 × 10	93.9		90.0	88.9	87.3	6.6
	15 × 15	95.3		92.1	91.5	90.9	4.4
	20 × 20	96.6		94.0	93.4	92.9	3.7
	25 × 25	97.4		95.1	94.5	94.2	3.2
1.0	5 × 5	99.4		97.3	92.4	84.5	14.9
	10 × 10	99.8		98.2	97.4	94.9	4.9
	15 × 15	99.9		99.2	98.4	97.4	2.5
	20 × 20	99.9		99.4	99.0	98.3	1.6
	25 × 25	99.9		99.8	99.3	98.8	1.1
1.5	5 × 5	99.8		99.1	95.2	87.2	12.6
	10 × 10	99.9		99.5	95.2	96.5	3.4
	15 × 15	99.8		99.7	99.2	98.5	1.3
	20 × 20	100.0		99.9	99.4	98.8	1.2
	25 × 25	99.9		100.0	99.5	99.2	0.7

*Value after application of correction factor (C_i [L]),[5] **Value obtained by subtracting the D_s value without (0.0 cm) and with 3.0 cm air gap