The software IsoCheck epid helps the medical physics expert to ensure the correct positioning of the LINAC radiological rotational isocenters. This is done by comparing the position of a high density ball (ISOBALL T42037) aligned to the treatment room lasers to the center of a radiation field irradiating this ball. The results can be displayed visually or numerically. Trends over time can be displayed in a separate QA statistics tab.