Fig. 3From: Association between postoperative radiotherapy for young-onset head and neck cancer and long-term risk of second primary malignancy: a population-based studySIRs and RRs for second primary malignancy. a External comparison of PORT-associated risk by estimating SIRs, taking the general population as a reference. b Internal comparison of PORT-associated risk by estimating RRs. SIR, standardized incidence ratio; RR, relative risk; PORT, postoperative radiotherapyBack to article page