Abstract: Disclosed is a medical system (100, 500) that comprises a radiotherapy system (102) configured for controllably irradiating a target volume (114) within an irradiation zone (112); a subject support (120) configured for supporting at least a ventral region (124) of a subject (122) within the irradiation zone; a breath monitor system (132, 132?) configured for providing a motion signal (154, 158) descriptive of subject breathing motion; and a subject display (130, 130?) configured for displaying a breathing phase indicator (160, 160?) to the subject when supported by the subject support. Execution of the machine executable instructions (150) causes a processor (142) controlling the medical system to receive (200) a time resolved magnetic resonance imaging dataset (152) synchronized to a measured motion signal (154).

Abstract: Disclosed herein is a medical system (100, 300, 500) comprising a processor (104) configured for controlling the medical system and a memory (110) for storing machine executable instructions. Execution of the instructions causes the processor to receive (200) four-dimensional Dixon magnetic resonance image data (122). The four-dimensional Dixon magnetic resonance imaging data is T1 weighted. The four-dimensional Dixon magnetic resonance image data is synchronized to a respiratory signal (124). Execution of the instructions further causes the processor to reconstruct (202) synthetic four-dimensional computed tomographic image data (12) from the four-dimensional Dixon magnetic resonance imaging data. The four-dimensional Dixon magnetic resonance imaging data is synchronized to the respiratory signal.