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

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.Forty of 870 patients were diagnosed with TLI after IMRT, the clinical and dosimetric characteristics of these TLI were analyzed.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 D1 cc (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 D1 cc<52 Gy, and the 5-year incidence of TLI in patients with Dmax 64-68 Gy or D1 cc 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 D1 cc exceeding 52 Gy; TLI is correlated with Dmax (r=0.89, P<0.01) and D1 cc (r=0.87, P<0.01) respectively.The incidence of TLI is relatively high, especially for patients with advanced T-stage NPC, and correlated with Dmax and D1 cc. IMRT with Dmax<68 Gy or D1 cc<58 Gy in TLs is relatively safe.