The study consists in the retrospective and prospective collection of imaging data (along with clinical information related to treatment) of skull-base chordoma patients treated with particle therapy, to derive imaging biomarkers which, integrated with advanced mathematical models, will allow predicting treatment outcome on a multi-scale basis.

The study design consists of the retrospective collection of routinely-acquired data (CT, MRI and dose maps, along with relevant clinical information) and the prospective acquisition of optimized non-invasive MR imaging data, of skull-based chordoma patients treated with particle therapy (PT) at the National Center for Oncological Hadrontherapy (CNAO, Pavia, Italy).

This data will be stored in a proper repository under CNAO's control, shared with Politecnico di Milano through encrypted channels, and it will be used to implement mathematical models able to predict treatment outcome at different scales (macroscopic, microscopic and radiobiological).

Inclusion Criteria:

• Patients with histologically confirmed diagnosis of chordoma of the skull base
• Particle therapy with curative intent
• Karnofsky Performance status greater than or equal to 60
• Patients with macroscopic disease detectable at pre-radiotherapy imaging
• Patients undergoing PT with standardized treatment procedures
• Patients who have signed the written informed consent for research

Exclusion Criteria:

• Metastatic disease
• Palliative treatment
• Other malignancies with disease-free interval < 5 years (excepting pre- cancerous lesions)
• Pregnancy
• Simultaneous CHT or Immunotherapy
• Extensive metal instrumentation/implants
• Patients with autoimmune diseases (ADs) -including collagen-vascular (CVD) and inflammatory bowel (IBD)

skull-based chordoma patients treated with particle therapy at the National Center for Oncological Hadrontherapy (CNAO, Pavia, Italy).