Clinical and dosimetric characteristics of temporal lobe injury following intensity modulated radiotherapy of nasopharyngeal carcinoma

Background and purpose: To evaluate the temporal lobe injury (TLI) in nasopharyngeal carcinoma (NPC) patients who had received intensity modulated radiotherapy (IMRT) and to assess the dosimetric parameters associated with TLI. Materials and methods: Forty of 870 patients were diagnosed with TLI after IMRT, the clinical and dosimetric characteristics of these TLI were analyzed. Results: A total of 4.6% (40/870) patients have developed TLI. However, TLI is not observed in T1–2 patients, the incidences are 3.1% and 13.4% in T3 and T4 patients respectively. The Dmax (maximum point dose, Gy) and D1cc (the dose delivered to the 1 cubic centimeter volume, Gy) in injured temporal lobes (TLs) are greater than that in normal TLs (P < 0.01). TLI is not observed in TLs with Dmax < 64 Gy or D1cc < 52 Gy, and the 5-year incidence of TLI in patients with Dmax 64–68 Gy or D1cc 52–58 Gy is <5.0%. A linear regression demonstrates a 2.6% augment of TLI per Gy of Dmax exceeding 64 Gy and a 2.5% augment of TLI per Gy of D1cc exceeding 52 Gy; TLI is correlated with Dmax (r = 0.89, P < 0.01) and D1cc (r = 0.87, P < 0.01) respectively. Conclusions: The incidence of TLI is relatively high, especially for patients with advanced T-stage NPC, and correlated with Dmax and D1cc. IMRT with Dmax < 68 Gy or D1cc < 58 Gy in TLs is relatively safe.