Deep learning based ultra‐low dose fan‐beam computed tomography image enhancement algorithm: Feasibility study in image quality for radiotherapy

Abstract Objective We investigated the feasibility of deep learning‐based ultra‐low dose kV‐fan‐beam computed tomography (kV‐FBCT) image enhancement algorithm for clinical application in abdominal and pelvic tumor radiotherapy. Methods A total of 76 patients of abdominal and pelvic tumors were prospectively selected. The Catphan504 was acquired with the same conditions as the standard phantom test set. We used a CycleGAN‐based model for image enhancement. Normal dose CT (NDCT), ultra‐low dose CT (LDCT) and deep learning enhanced CT (DLR) were evaluated by subjective and objective analyses in terms of imaging quality, HU accuracy, and image signal‐to‐noise ratio (SNR). Results The image noise of DLR was significantly reduced, and the contrast‐to‐noise ratio (CNR) was significantly improved compared to the LDCT. The most significant improvement was the acrylic which represented soft tissue in CNR from 1.89 to 3.37, improving by 76%, nearly approaching the NDCT, and in low‐density resolution from 7.64 to 12.6, improving by 64%. The spatial frequencies of MTF10 and MTF50 in DLR were 4.28 and 2.35 cycles/mm in DLR, respectively, which are higher than LDCT 3.87 and 2.12 cycles/mm, and even slightly higher than NDCT 4.15 and 2.28 cycles/mm. The accuracy and stability of HU values of DLR were similar to NDCT. The image quality evaluation of the two doctors agreed well with DLR and NDCT. A two‐by‐two comparison between groups showed that the differences in image scores of LDCT compared with NDCT and DLR were all statistically significant ( p < 0.05), and the subjective scores of DLR were close to NDCT. Conclusion The image quality of DLR was close to NDCT with reduced radiation dose, which can fully meet the needs of conventional image‐guided adaptive radiotherapy (ART) and achieve the quality requirements of clinical radiotherapy. The proposed method provided a technical basis for LDCT‐guided ART.