Some embodiments include determination of a first projection image of a phantom based on first imaging geometry parameters associated with a first radiation-based imaging system and on a virtual model of the phantom, acquisition of a second projection image of the phantom based on radiation emitted from the first radiation-based imaging system, the phantom located at a first position and determination of a difference between the first projection image and the second projection image. Second imaging geometry parameters are determined based on the first imaging geometry parameters and the difference between the first projection image and the second projection image, a third projection image of the phantom is determined based on the second imaging geometry parameters and on the virtual model of the phantom, and a fourth projection image of the phantom located at the first position is acquired based on radiation emitted from the first radiation-based imaging system. A difference between the third projection image and the fourth projection image is determined and it is determined that the difference between the third projection image and the fourth projection image is less than a threshold.