Some embodiments include determination of a first misalignment between an imaging device and an axis of a radiation beam emitted from a treatment head, determination of a rotational misalignment between the imaging device and the treatment head within a plane normal to the axis of the radiation beam, acquisition of an image using the imaging device, and modification of the acquired image based on the determined first misalignment and rotational misalignment. Embodiments may further include determination of a second rotational misalignment between the imaging device and the plane normal to the axis of the radiation beam, and modification of the acquired image based on the determined first misalignment, rotational misalignment and second rotational misalignment.