“…Methodologies inspired on U-net [ 154 ] cover the majority of deep learning-based attempts [ 155 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 ]. To increase the complexity of the feature extraction task, the encoder module could reuse transferred weights from pre-trained networks, as in the works by Vu et al [ 163 ] and Jalali et al [ 166 ], where the VGG-16 and ResNet-34 models were adopted to work as encoder blocks, respectively. More investigations on improvements in typical convolutional blocks can also be found, integrating residual blocks [ 164 , 167 ], inception modules with dense connections [ 162 ], and squeeze-and-excitation blocks to target specific thoracic organs at risk [ 165 ].…”