A phantom setup and source-to-surface distance (SSD) verification method uses radiation images. In an exemplary method, a phantom is positioned on a support relative to a radiation source such that a surface of the phantom is horizontally leveled at or approximate to a desired value of SSD. The radiation source is then positioned at a gantry angle predetermined at least based on the desired value of SSD such that a ray of radiation from the radiation source aligns with a horizontal surface located at the desired value of SSD. An image is acquired using radiation from the radiation source at the predetermined gantry angle. Verification is performed to confirm, based on an analysis of the image, if the surface of the phantom is positioned at the desired value of SSD.
