A first self-calibration curve relates a first array image to a first acquired image, the first array image being recorded from application of a first radiation treatment plan to a detector array, and the first acquired image being recorded from application of the first radiation treatment plan to a radiation detector. At least one subsequent self-calibration curve relates at least one subsequent array image to at least one subsequent acquired image, the subsequent array image being recorded from application of at least one subsequent radiation treatment plan to the detector array, and the subsequent acquired image being recorded from application of the subsequent radiation treatment plan to the radiation detector. In some embodiments, the detector array is pre-calibrated to a predefined standard.