This upload contains the instructions and guidelines for the STOPSTORM.eu Center Accreditation Program benchmark, developed within the EU Horizon Europe project STOPSTORM (Grant Agreement ID: 945119). Two complementary benchmark exercises are provided: Critical Structures Contouring Benchmark: guidance for delineating cardiac and thoracic organs at risk (whole heart, cardiac chambers, left ventricle segments, valves, coronary arteries, great vessels, nodes, lungs, trachea, bronchus, esophagus, stomach, spinal canal and ICD) on three benchmark cases, each comprising a planning-CT and a co-registered contrast-enhanced cardiac-CT. Treatment Planning Benchmark: instructions for performing stereotactic arrhythmia radioablation (STAR) treatment plans on the same three cases, using the pre-contoured OARs and PTVs.