Inclusion Criteria:  Received or will receive stereotactic ablative body radiotherapy (SABR) treatment for liver cancer at a participating site. Received a radio-opaque contrast agent (e.g. Lipiodol™ or DC Bead LUMI™) that is visible on the radiation treatment planning CT scan The radio-opaque contrast agent mass is or will be within the x-ray imaging field of view during the CBCT scan and any planned intra-fraction imaging. Note that there is no requirement of the distance between the contrast agent mass and the treated tumour as the goal of the study is the contrast agent mass tracking. Provides written informed consent (prospectively recruited) or meets criteria for waiving of the requirement for consent (retrospectively recruited)  Exclusion Criteria:  Less than 18 years of age Minimum image dataset is not available Image dataset is not in a compatible format