Half-Brain Delineation For Prediction Of Radiation-Induced Temporal Lobe Injury In Nasopharyngeal Carcinoma Receiving Intensity-Modulated Radiotherapy

PurposeTo 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).Methods and MaterialsA 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.ResultsCVs 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(V)s 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(D)s 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.ConclusionHalf-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 V70-73Gy could be considered when the high dose is inevitable.