A 4D CT sorting algorithm based on image boundary discontinuity

Respiration induces significant movements of thorax and abdomen, which shift target site and thus degrade the accuracy and efficacy of radiotherapy. 4D CT sorting is an indispensable and important step to retrospectively rearrange the reconstructed CT images sampled at scan positions to get a set of volume images corresponding to different respiratory phases. Currently, most current sorting methods depend on external surrogates of respiratory motion, which may not always accurately catch the internal motion especially when irregular breathing occurs and lead to severe image artifacts. The 4D CT images produced by our method present fewer artifacts than that by RPM phase-based sorting, which shows that our method is feasible to sort 4D CT images without using external motion monitoring system.