Table 1.

Basic characteristics of the included studies

Author	Year	Nation	Study design	SCC/AC	TNM stage	Groups	Patients Number	Radiation dose#	Category of RT type
He et al 14	2014	USA	Retrospective	193/0	I-IV	Standard dose	137	Median: 50.4 Gy (41.4-50.4 Gy)	3D-CRT, IMRT and Proton therapy
						High dose	56	Median: 60 Gy (52.2-66 Gy)
Chen et al 15	2016	China	Retrospective*	648/0	I-IV	Standard dose	324	50-50.4 Gy	3D-CRT and IMRT
						High dose	324	≥60 Gy
Chang et al 16	2017	China	Retrospective	2061/0	IA-IIIC	Standard dose	1134	Median: 50.4 Gy (45-59.4 Gy)	IMRT
						High dose	927	Median: 66.6 Gy (60-72 Gy)
Kim et al 17	2017	Korea	Retrospective	230/6	II-III	Standard dose	120	Median: 50.4 Gy (45-59.4 Gy)	3D-CRT and IMRT
						High dose	116	Median: 63 Gy (60-66.6 Gy)
Nayan et al 18	2018	India	Prospective	28/0	II-III	Standard dose	14	50.4 Gy	3D-CRT and IMRT
						High dose	14	64.8 Gy
Ren et al 19	2018	China	Retrospective*	380/0	I-IV	Standard dose	190	50.4-54 Gy	3D-CRT and IMRT
						High dose	190	60 Gy
Ke et al 23	2018	China	Retrospective	84/0	I-III	Standard dose	42	Median: 49.5 Gy (44-50.4 Gy)	IMRT and Conformal Arc
						High dose	42	Median: 61.8 Gy (52.2-70 Gy)
Welsh et al 25	2016	USA	Retrospective	45/89	I-IV	Standard dose	97	50.4 Gy	IMRT and Proton therapy
						High dose	38	Median: 63 Gy (58.8-63 Gy)
Clavier et al 26	2013	France	Retrospective	113/30	I-IV	Standard dose	60	Median: 50Gy (38-50.4 Gy)	3D-CRT and IMRT
						High dose	83	Median: 66Gy (50.7-72 Gy)
Higuchi et al 27	2014	Japan	Retrospective	42/0	I-IV	Standard dose	30	50.4 Gy	3D-CRT and IMRT
						High dose	12	61.2 Gy
Nemoto et al 28	2020	Japan	Retrospective	951/17	I-IV	Standard dose	171	50.4Gy	3D-CRT and IMRT
						High dose	825	60Gy

SCC, squamous cell carcinoma; AC, adenocarcinoma;

3D-CRT, 3-Dimensional conformal radiotherapy; IMRT, Intensity-modulated radiation therapy;

# Median radiation dose and the dose range of the whole group.

*Construct a propensity score matched cohort (1:1 for high dose vs standard dose).