Automatic segmentation of organs at risk for nasopharyngeal carcinoma with Smart Segmentation and MIM Atlas

Objective To compare the accuracy of two automatic segmentation softwares (Smart Segmentation and MIM Atlas) in organs at risk (OARs) contouring for nasopharyngeal carcinoma (NPC). Methods Totally 55 NPC patients were retrospectively reviewed with manually contoured OARs on CT images, in which 30 cases were randomly selected to create a data base in the Smart Segmentation and MIM Atlas. The remaining 25 cases were automatically contoured with Smart Segmentation and MIM as test cases. The automatic contouring accuracies of two softwares were evaluated with Dice coefficient(DSC), Hausdorff distance(HD), and absolute volume difference(△V) using manual contours as a golden standard. Results The overall DSC, HD and △V of all organs contoured by MIM Atlas and Smart Segmentation were (0.79±0.13) vs. (0.62±0.24) (t=14.06, P<0.05), (5.50±3.84)mm vs.(8.38±4.88)mm (t=-11.40, P<0.05), and (1.52±2.46) cm3vs. (2.38±3.57) cm3 (t=-4.70, P<0.05), respectively. The average DSC of 11 organs (brain stem, optic chiasm, bilateral lens, bilateral optic nerve, bilateral eyeballs, bilateral parotid gland, spinal cord) delineated by MIM Atlas was statistically greater than that of Smart Segmentation (t=5.27, 4.41, 6.34, 5.70, 10.62, 7.45, 3.96, 4.26, 6.25, 5.42, 7.23, P<0.05). The average HD of 10 organs (brain stem, optic chiasm, bilateral lens, bilateral optic nerve, bilateral eyeballs, left parotid gland, spinal cord) delineated by MIM Atlas was statistically less than that of Smart Segmentation (t=-4.51, -4.49, -3.92, -3.45, -5.36, -5.56, -3.89, -3.90, -3.60, -3.68, P<0.05). The average △V of 6 organs (brain stem, optic chiasm, left len, bilateral optic nerve, right eyeball) delineated by MIM Atlas was statistically less than that of Smart Segmentation (t=-2.83, -3.39, -2.56, -2.27, -2.43, -2.51, P<0.05). Conclusions Both softwares have reasonable contouring accuracy for larger organs. The accuracy decreased with the decrease of organ volumes and blurred boundary. Generally, MIM Atlas′s performs better than Smart Segmentation does. Key words: Automatic contouring; Organs-at-risk segmentation; Atlas library; Nasopharyngeal carcinoma