PET–CT	positron emission tomography–computed tomography
18FDG-PET–CT	18-fluorodeoxyglucose positron emission tomography–computed tomography
HR	hazard ratio
aHR	adjusted hazard ratio
CI	confidence interval
NCCN	National Comprehensive Cancer Network
RCT	randomized controlled trial
PSM	propensity score matching
HWDC	Health and Welfare Data Center
NHI	National Health Insurance
AJCC	American Joint Committee on Cancer
CCI	Charlson comorbidity index
OS	overall survival
ICD-10-CM	International Classification of Diseases, Tenth Revision, Clinical Modification
ICD-9-CM	International Classification of Diseases, Ninth Revision, Clinical Modification
RT	radiotherapy
CCRT	concurrent chemoradiotherapy
CT	computed tomography
MRI	magnetic resonance imaging
NHIRD	National Health Insurance Research Database
SCC	squamous cell carcinoma