Half-Brain Delineation for Prediction of Radiation-Induced Temporal Lobe Injury in Nasopharyngeal Carcinoma Receiving...

To investigate the role of half-brain delineation in the prediction of radiation-induced temporal lobe injury (TLI) in nasopharyngeal carcinoma (NPC) receiving intensity-modulated radiotherapy (IMRT).

A total of 220 NPC cases treated with IMRT and concurrent platinum-based chemotherapy were retrospectively analyzed. Dosimetric parameters of temporal lobes, half-brains, and brains included maximum dose (D_max), doses covering certain volume (D_V) from 0.03 to 20 cc and absolute volumes receiving specific dose (V_D) from 40 to 80 Gy. Inter-structure variability was assessed by coefficients of variation (CV) and paired samples t-tests. Receiver operating characteristic curve (ROC) and Youden index were used for screening dosimetric parameters to predict TLI. Dose/volume response curve was calculated using the logistic dose/volume response model.

CVs of brains, left/right half-brains, and left/right temporal lobes were 9.72%, 9.96%, 9.77%, 27.85%, and 28.34%, respectively. Each D_V in temporal lobe was significantly smaller than that in half-brain (P < 0.001), and the reduction ranged from 3.10% to 45.98%. The area under the curve (AUC) of D_V and V_D showed an "increase-maximum-decline" behavior with a peak as the volume or dose increased. The maximal AUCs of D_Vs in brain, half-brain and temporal lobe were 0.808 (D_2cc), 0.828 (D_1.2cc) and 0.806 (D_0.6cc), respectively, and the maximal AUCs of V_Ds were 0.818 (D_75Gy), 0.834 (V_72Gy) and 0.814 (V_70Gy), respectively. The cutoffs of V_70Gy (0.86 cc), V_71Gy (0.72 cc), V_72Gy (0.60 cc), and V_73Gy (0.45 cc) in half-brain had better Youden index. TD5/5 and TD50/5 of D_1.2cc were 58.7 and 80.0 Gy, respectively. The probability of TLI was higher than >13% when V_72Gy>0 cc, and equal to 50% when V_72Gy = 7.66 cc.

Half-brain delineation is a convenient and stable method which could reduce contouring variation and could be used in NPC patients. D_1.2cc and V_72Gy of half-brain are feasible for TLI prediction model. The dose below 70 Gy may be relatively safe for half-brain. The cutoff points of V_70-73Gy could be considered when the high dose is inevitable.