Table 3.

Cox proportional hazards regression analysis for progression-free survival

Variable	HR	95% CI	P value
Age ≥ 60 years	1.90	0.84–4.28	0.122
OTT of RT > 61 days	1.61	0.69–3.78	0.273
T3 or T4 disease	2.72	1.30–5.71	0.008
N1 or N2 disease	2.55	1.15–5.63	0.021
Pretreatment SCC Ag > 10 ng/mL	2.20	1.03–4.71	0.041
Post-treatment SCC Ag > 1.5 ng/mL	2.01	0.82–4.96	0.129
EQD2 of Point A ≥ 81 Gy	1.39	0.65–2.97	0.403
RT techniquea			0.423
VMAT	0.53	0.13–2.08	0.359
Tomotherapy	0.91	0.25–3.33	0.889

HR hazard ratio, CI confidence interval, OTT overall treatment time, RT radiation therapy, SCC Ag squamous cell carcinoma antigen, EQD2 equivalent dose in 2-Gy fractions, VMAT volumetric modulated arc therapy

^aReference category: 3DCRT, three-dimensional conformal radiation therapy