Table I.

Numerical comparison among CBCT, sCT generated by U-Net, with and without AG

	CBCT	U-Net	CycleGAN	CycleGAN with AC
MAE (HU)	81.06 ± 15.86	66.71 ± 15.82	63.72 ± 10.55	56.89 ± 13.84
SNU	0.25 ± 0.097	0.19 ± 0.088	0.15 ± 0.096	0.12 ± 0.085
PSNR (dB)	22.89 ± 2.89	28.17 ± 3.34	25.69 ± 3.40	28.80 ± 2.46
NCC	0.85 ± 0.081	0.87 ± 0.033	0.94 ± 0.040	0.96 ± 0.022
SSIM	0.60 ± 0.063	0.56 ± 0.085	0.70 ± 0.044	0.71 ± 0.032

AG, attention gate; CBCT, cone-beam CT; MAE, mean absolute error; PSNR, peak signal to noise ratio; SNU, spatial nonuniformity; sCT, synthetic CT.