Real-time deep neural network-based automatic bowel gas segmentation on X-ray images for particle beam treatment

Since particle beam distribution is vulnerable to change in bowel gas because of its low density, we developed a deep neural network (DNN) for bowel gas segmentation on X-ray images. We used 6688 image datasets from 209 cases as training data, 736 image datasets from 23 cases as validation data and 102 image datasets from 51 cases as test data (total 283 cases). For the training data, we prepared three types of digitally reconstructed radiographic (DRR) images (all-density, bone and gas) by projecting the treatment planning CT image data. However, the real X-ray images acquired in the treatment room showed low contrast that interfered with manual delineation of bowel gas. Therefore, we used synthetic X-ray images converted from DRR images in addition to real X-ray images.We evaluated DNN segmentation accuracy for the synthetic X-ray images using Intersection over Union, recall, precision, and the Dice coefficient, which measured 0.708 +/- 0.208, 0.832 +/- 0.170, 0.799 +/- 0.191, and 0.807 +/- 0.178, respectively. The evaluation metrics for the real X-images were less accurate than those for the synthetic X-ray images (0.408 +/- 0237, 0.685 +/- 0.326, 0.490 +/- 0272, and 0.534 +/- 0.271, respectively). Computation time was 29.7 +/- 1.3 ms/image. Our DNN appears useful in increasing treatment accuracy in particle beam therapy.