The error estimate for contouring the brainstem in radiotherapy of head and neck cancer: a multi-center study from north China.

PURPOSE To analyze the error in contouring the brainstem for patients with head and neck cancer who underwent radiotherapy (RT) based on computed tomography (CT) and magnetic resonance (MR) images. METHODS 20 patients with brain tumor and 17 patients with nasopharyngeal cancer (NPC) were randomly selected. Each patient underwent MR and CT scanning. For each patient, one observer contoured the brainstem on CT and MR images 10 times, and 10 observers from 5 centers delineated the brainstem on CT and MR images only one time. The inter- and intra-observers volume and outline variations were compared. RESULTS The volumes of brainstem contoured by inter and intra-observers on CT and MR images were similar (p>0.05). The reproducibility of contouring brainstem on MR images was better than that on CT images (p<0.05) for both inter- and intra-observer variability. The inter- and intra-observer variability for contouring the brainstem on CT images reached mean values of 0.81±0.05 (p>0.05) and of 0.85±0.05 (p>0.05), respectively, while on MR images the respective values were 0.90±0.05 (p>0.05) and 0.92±0.04 (p>0.05). CONCLUSION Contouring the brainstem on MR images was more accurate and reproducible than that on CT images. Precise information might be more helpful for the patients whose lesion were closed to brainstem.