Radiation-induced temporal lobe injury after intensity modulated radiotherapy in nasopharyngeal carcinoma patients: a dose-volume-outcome analysis

BACKGROUND: To identify the radiation volume effect and significant dosimetric parameters for temporal lobe injury (TLI) and determine the radiation dose tolerance of the temporal lobe (TL) in nasopharyngeal carcinoma (NPC) patients treated with intensity modulated radiation therapy (IMRT). METHODS: Twenty NPC patients with magnetic resonance imaging (MRI)-diagnosed unilateral TLI were reviewed. Dose-volume data was retrospectively analyzed. RESULTS: Paired samples t-tests showed all dosimetric parameters significantly correlated with TLI, except the TL volume (TLV) and V(75) (the TLV that received ≥75 Gy, P = 0.73 and 0.22, respectively). Receiver operating characteristic (ROC) curves showed V(10) and V(20) (P = 0.552 and 0.11, respectively) were the only non-significant predictors from V(10) to V(70) for TLI. D(0.5cc) (dose to 0.5 ml of the TLV) was an independent predictor for TLI (P < 0.001) in multivariate analysis; the area under the ROC curve for D(0.5cc) was 0.843 (P < 0.001), and the cutoff point 69 Gy was deemed as the radiation dose limit. The distribution of high dose ‘hot spot’ regions and the location of TLI were consistent. CONCLUSIONS: A D(0.5cc) of 69 Gy may be the dose tolerance of the TL. The risk of TLI was highly dependent on high dose ‘hot spots’ in the TL; physicians should be cautious of such ‘hot spots’ in the TL during IMRT treatment plan optimization, review and approval.