Higher accuracy and lower complexity: convolutional neural network for multi-organ segmentation

In computed tomography (CT), segmentation of organs-at-risk (OARs) is a key task in formulating the radiation therapy (RT) plan. However, it takes a lot of time to delineate OARs slice by slice in CT scans. The proposal of deep convolutional neural networks makes it possible to effectively segment medical images automatically. In this work, we propose an improved 2D U-Net to segment multiple OARs, aiming to increase accuracy while reducing complexity. Our method replaces vanilla convolutions with Octave Convolution (OctConv) units to reduce memory use and computation cost without accuracy sacrifice. We further plug a ‘Selective Kernel’ (SK) block after the encoder to capture multi-scale information and adaptively recalibrate the learned feature maps with attention mechanism. An in-house dataset is used to evaluate our method, where four chest organs are involved: left lung, right lung, heart, and spinal cord. Compared with the naive U-Net, the proposed method can improve Dice by up to nearly 3% and has fewer float-point operations (FLOPs).