Table 2.

Measured surface doses relative to the dose maximum $({\mathrm{D}}_{max})$ (in percentage) with different couch inserts in the beam with energies of 6 and 15 MV. Measurements were performed with $10\times 10\hspace{0.17em}{\text{cm}}^2$ and $20\times 20\hspace{0.17em}{\text{cm}}^2$ open fields with a direct posterior beam (gantry angle 180°). The corrected surface dose takes into account the perturbation effect of the used plane‐parallel ionization chamber. The couch inserts are in descending order with respect to relative surface dose.

	6 MV		15 MV
	$10\times 10\hspace{0.17em}c{m}^2$	$20\times 20\hspace{0.17em}c{m}^2$	$10\times 10\hspace{0.17em}c{m}^2$	$20\times 20\hspace{0.17em}c{m}^2$
Measured Surface Dose	44.3	53.4	27.6	39.1
Corrected Surface Dose	35.2	44.3	21.0	32.6
Dose at Dmax	100.0	100.0	100.0	100.0
BrainLAB	98.6	99.4	84.5	89.9
Varian Exact IGRT	90.8	94.0	69.6	77.7
Universal Sandwich Panel	90.2	93.2	69.2	76.9
MEDTEC	90.1	93.4	69.1	77.3
Qfix kVue Standard	88.5	92.1	66.9	75.2
DIGNITY AirPlate	86.0	89.8	66.0	74.3
Qfix kVue DoseMax	75.1	80.9	52.8	63.0
Varian Grid Insert	61.2	69.0	41.0	51.7