European guideline for imaging of primary paediatric and adult osteosarcoma and Ewing sarcoma: systematic review and joint statement by the FOSTER consortium, Euro Ewing Consortium, European Society of Paediatric Radiology, and the European Association of Nuclear Medicine.

Imaging is central to diagnosing, staging, evaluating treatment response, and guiding post-therapy surveillance in osteosarcoma and Ewing sarcoma, yet no international consensus defines optimal modalities or schedules. This European guideline, developed by 36 multidisciplinary experts, seeks to standardise imaging for research and enhance patient care. A systematic review identified 2026 studies, of which 13 met criteria, revealing marked heterogeneity in diagnoses, chemotherapy regimens, and imaging protocols. Evidence remains inconclusive regarding the optimal modality for detecting bone metastases, and no metabolic imaging indices or MRI parameters consistently predict response or survival. Data are similarly insufficient to define the ideal frequency of post-treatment surveillance. Recommendations for clinical practice were formulated according to International Guideline Harmonization Group standards, based on evidence and expert opinion. In total, 32 consensus-based recommendations were issued. Substantial evidence gaps persist, underscoring the need for international prospective imaging studies to establish robust, harmonised standards for future patient care.