A radiotherapy delivery device comprising: a rotatable gantry system positioned at least partially around a patient support; a first source of radiation coupled to the rotatable gantry system, the first source of radiation being configured as a source of therapeutic radiation; a second source of radiation coupled to the rotatable gantry system, the second source of radiation being configured as a source of imaging radiation having an energy level less than the source of therapeutic radiation; a radiation detector coupled to the rotatable gantry system and positioned to receive radiation from the second source of radiation; a beamformer configured to adjust a shape of a radiation beam emitted by the second source of radiation, such that the shape of the radiation beam is configured for a wide aperture scan of a wide axial region and a narrow aperture scan of a narrow axial region within the wide axial region; and a data processing system configured to: receive measured projection data in the wide axial region and the narrow axial region; determine the estimated scatter in the wide axial region using a kernel-based technique, wherein the estimated scatter in the wide axial region is based on the projection data from the narrow axial region; reconstruct a patient image based on the estimated scatter; and deliver a dose of therapeutic radiation to the patient via the first radiation source based on the patient image during Adaptive Image-Guided Radiation Therapy (IGRT). a rotatable gantry system positioned at least partially around a patient support; a first source of radiation coupled to the rotatable gantry system, the first source of radiation being configured as a source of therapeutic radiation; a second source of radiation coupled to the rotatable gantry system, the second source of radiation being configured as a source of imaging radiation having an energy level less than the source of therapeutic radiation; a radiation detector coupled to the rotatable gantry system and positioned to receive radiation from the second source of radiation; a beamformer configured to adjust a shape of a radiation beam emitted by the second source of radiation, such that the shape of the radiation beam is configured for a wide aperture scan of a wide axial region and a narrow aperture scan of a narrow axial region within the wide axial region; and a data processing system configured to: receive measured projection data in the wide axial region and the narrow axial region; determine the estimated scatter in the wide axial region using a kernel-based technique, wherein the estimated scatter in the wide axial region is based on the projection data from the narrow axial region; reconstruct a patient image based on the estimated scatter; and deliver a dose of therapeutic radiation to the patient via the first radiation source based on the patient image during Adaptive Image-Guided Radiation Therapy (IGRT). receive measured projection data in the wide axial region and the narrow axial region; determine the estimated scatter in the wide axial region using a kernel-based technique, wherein the estimated scatter in the wide axial region is based on the projection data from the narrow axial region; reconstruct a patient image based on the estimated scatter; and deliver a dose of therapeutic radiation to the patient via the first radiation source based on the patient image during Adaptive Image-Guided Radiation Therapy (IGRT).