A system for performing a treatment fraction of radiation therapy, the system comprising: an X-ray imager; a treatment-delivering X-ray source configured to direct treatment X-rays to a target volume of patient anatomy; an imaging X-ray source configured to direct imaging X-rays through the target volume and toward the X-ray imager; and a processor; a signal bearing medium including one or more sets of executable instructions that, when executed by said processor, provide the functionality of: while a patient is disposed in a first position and maintains a first inspiration level, acquire a set of projection images, generated by the X-ray imager, of the target volume associated with the patient; characterized by further providing the functionality of: based on a treatment planning digital volume associated with the radiation therapy process (700, 800) and the set of projection images, generate a synthetic digital volume that includes the target volume; based on a treatment plan associated with the treatment planning digital volume and on the synthetic digital volume, generate a modified treatment fraction; and while the patient remains in the first position and maintains at least the first inspiration level, cause the modified treatment fraction to be performed by the treatment-delivering X-ray source. an X-ray imager; a treatment-delivering X-ray source configured to direct treatment X-rays to a target volume of patient anatomy; an imaging X-ray source configured to direct imaging X-rays through the target volume and toward the X-ray imager; and a processor; a signal bearing medium including one or more sets of executable instructions that, when executed by said processor, provide the functionality of: while a patient is disposed in a first position and maintains a first inspiration level, acquire a set of projection images, generated by the X-ray imager, of the target volume associated with the patient; characterized by further providing the functionality of: based on a treatment planning digital volume associated with the radiation therapy process (700, 800) and the set of projection images, generate a synthetic digital volume that includes the target volume; based on a treatment plan associated with the treatment planning digital volume and on the synthetic digital volume, generate a modified treatment fraction; and while the patient remains in the first position and maintains at least the first inspiration level, cause the modified treatment fraction to be performed by the treatment-delivering X-ray source. while a patient is disposed in a first position and maintains a first inspiration level, acquire a set of projection images, generated by the X-ray imager, of the target volume associated with the patient; characterized by further providing the functionality of: based on a treatment planning digital volume associated with the radiation therapy process (700, 800) and the set of projection images, generate a synthetic digital volume that includes the target volume; based on a treatment plan associated with the treatment planning digital volume and on the synthetic digital volume, generate a modified treatment fraction; and while the patient remains in the first position and maintains at least the first inspiration level, cause the modified treatment fraction to be performed by the treatment-delivering X-ray source. based on a treatment planning digital volume associated with the radiation therapy process (700, 800) and the set of projection images, generate a synthetic digital volume that includes the target volume; based on a treatment plan associated with the treatment planning digital volume and on the synthetic digital volume, generate a modified treatment fraction; and while the patient remains in the first position and maintains at least the first inspiration level, cause the modified treatment fraction to be performed by the treatment-delivering X-ray source.