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

Abstract

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 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.

Conclusions: 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.