A method includes positioning a patient at a first orientation relative to a radiation source. The method further includes using a 3D imaging technique to measure one or more positions of the patient's chest. The method further includes, while using the 3D imaging technique to measure the one or more positions of the patient's chest: generating a model of the patient's chest using the one or more positions of the patient's chest; updating the model of the patient's chest as the patient breathes; and exposing the patient to a dose of radiation using the radiation source, wherein the dose is based on the model of the patient's chest.