Asymptomatic temporal lobe injury after radiotherapy for nasopharyngeal carcinoma: incidence and determinants.

Computed tomography (CT) scans were performed on a cohort of 60 patients for detection of temporal lobe injury (TLI) at 1-3.5 years after radiation therapy for nasopharyngeal carcinoma. Nine cases of TLI were identified, five of which were asymptomatic. The earliest case of asymptomatic TLI was found at 2.2 years after radiation therapy and the earliest symptomatic case at 2.3 years. A significantly higher incidence of TLI was found in patients with decreased temporal lobe shielding consequent to omitted eyeshield to the anterior photon beam and in patients treated with a hyperfractionation schedule giving 67.2 Gy in 42 fractions in 6 weeks. The incidence in these subgroups at 2-3.5 years after radiation therapy was 56% (5/9 patients) and 35% (8/23 patients), respectively. No patient in this study had TLI in the absence of these two factors. The implications of the results are discussed.