Table 2. Multivariate analysis of prognostic factors in the 291 patients with locally recurrent NPC receiving salvage IMRT.

Endpoint	Variable	HR	95% CI	P value
LFFS	Recurrent T classification* (rT3-4vs. r1-2)	3.837	1.543–9.542	0.004
DMFS	TV	1.013	1.004–1.022	0.003
OS	TV	1.015	1.011–1.020	<0.001
	Age	1.025	1.012–1.038	<0.001
	Recurrent T classification* (rT3-4vs. r1-2)	1.916	1.206–3.042	0.006
	Recurrence interval	0.994	0.990–0.998	0.003
TRD	TV	1.014	1.007–1.021	<0.001
	Age	1.026	1.007–1.045	0.006
	Recurrence interval	0.994	0.989–1.000	0.048

Abbreviations: TV, gross recurrent tumor volume; HR, hazard ratio; CI, confidence interval; LFFS, local failure-free survival; DMFS, distant metastasis-free survival; OS, overall survival; TRD, toxicity-related death.

* According to the 7th AJCC/UICC staging system. The following parameters were included in the Cox proportional hazards model by backward elimination: recurrence interval as a continuous variable, age as a continuous variable, gender (female vs. male), World Health Organization (WHO) histological grade (Type II vs. Type I), recurrent T classification (rT3-4 vs. rT1-2), recurrent N classification (rN1-3 vs. rN0), initial radiotherapy dose (>70Gy vs. ≤ 70Gy), use of chemotherapy (with vs. without) and TV as a continuous variable.