Artificial intelligence in rectal cancer

Table 1 Target volume and organs at risk contouring with artificial intelligence

Ref.	Number of patients	Imaging method	Contouring	Artificial intelligence method	Results
Wang et al[54], 2018	93	MR (3 Tesla, T2 -weighted)	GTV, CTV	CNN	Between deep learning-based autosegmentation and manual contouring DSC (P = 0.42), JSC (P = 0.35), HD (P = 0.079), and ASD (P = 0.16); Before postprocess process only in HD (P = 0.0027).
Trebeschi et al[55], 2017	140	Multiparametric MRI (1.5 Tesla, T2- weighted)	GTV	CNN	According to CNN and both radiologists in independent validation data set DSC: 0.68 and 0.70; For both radiologists AUC: 0.99.
Song et al[56], 2020	199	CT (3 mm section thickness)	CTV and OAR	CNNs (DeepLabv3+ and ResUNet)	CTV segmentation better with DeepLabv3+ than ResUNet (volumetric DSC, 0.88 vs 0.87, P = 0.0005; surface DSC, 0.79 vs 0.78, P = 0.008); DeepLabv3+ model segmentation was better in the small intestine, with the ResUNet model, bladder and femoral heads segmentation results were better. In both models, the OAR manual correction time was 4 min.
Men et al[60], 2017	278	CT (5 mm section thickness)	CTV and OAR	CNN (DDCNN)	DSC values; CTV: 87.7%, bladder: 93.4%, left femoral head: 92.1%, right femoral head: 92.3%, small intestine: 65.3%, colon 61.8%.
Men et al[61], 2018	100	CT (3 mm section thickness)	CTV and OAR	CNN	CTV and bladder contouring were better in the model trained in the same position than the model trained in a different position (P < 0.05). No statistically significant difference between femoral heads (P > 0.05). No statistical difference between accuracy rates in CTV, bladder, and femoral heads segmentation in the model trained in both positions (P > 0.05).

AUC: Area under the curve; ASD: Average surface distance; CNN: Convolutional neural network; CT: Computed tomography; CTV: Clinical target volume; DDCNN: Deep dilated convolutional neural network; DSC: Dice similarity coefficient; GTV: Gross tumor volume; HD: Hausdorff distance; JSC: Jaccard index; MRI: Magnetic resonance imaging; OAR: Organs at risk.