Table 4.

Cox proportional hazards model to predict variables associated with overall survival and progression free survival.

	Overall survival		Progression free survival
	HR (95% CI)	p	HR (95% CI)	p
Variables
Age: >58 years (Ref: ≦58 years)	1.4 (0.8–2.6)	0.28	1.2 (0.6–2.0)	0.61
Gender: female (Ref: male)	0.8 (0.3–2.7)	0.68	0.7 (0.2–2.4)	0.59
Smoking: yes (Ref: no)	0.9 (0.4–2.8)	0.97	1.2 (0.5–3.2)	0.68
Betel nut: yes (Ref: no)	1.1 (0.4–2.6)	0.95	0.7 (0.3–1.6)	0.38
P-16: positive (Ref: negative or unknown)	0.9 (0.4–1.9)	0.61	0.8 (0.4–1.9)	0.65
Primary cancer sites: others (Ref: oral cavity)	1.2 (0.6–2.4)	0.52	1.1 (0.6–2.1)	0.74
Original AJCC stage: IV (Ref: I-III)	1.0 (0.4–2.1)	0.93	1.2 (0.5–2.5)	0.70
Recurrent AJCC stage: rcIVb (Ref: rcIVa)	2.5 (0.7–9.7)	0.17	2.3 (0.6–8.7)	0.20
Re-irradiation interval: ≦12 months (Ref: >12 months)	3.3 (1.7–6.5)	<0.001	3.1 (1.6–5.9)	<0.001
SBRT sites: N or T + N (Ref: T)	0.8 (0.4–1.5)	0.45	0.9 (0.5–1.9)	0.92
SBRT dose: >40 Gy (Ref: 40 Gy)	0.6 (0.3–1.2)	0.12	0.6 (0.3–1.2)	0.16
Gross tumor volume: >50 ml (Ref:≦50 ml)	4.6 (2.1–9.9)	<0.001	3.5 (1.7–7.1)	0.001
Acne formation:≧grade 2 (Ref: grade 0–1)	0.6 (0.2–1.4)	0.22	0.6 (0.2–1.3)	0.16

Abbreviations: HR: Hazard ratio; CI: confidence interval; Ref: reference; SBRT: stereotactic body radiotherapy; T: gross tumor area; N: gross nodal area; AJCC: American Joint Committee on Cancer Staging System, 8th edition.