Radiotherapy remains a cornerstone of oncology care, particularly for rare or orphan cancers and chronic oncologic and rare non oncologic conditions, where precision and individualized treatment planning are necessary. Advances in imaging technologies are crucial to overcome the challenges posed by these cases, especially in achieving accurate tumor delineation and dose delivery. Photon-counting CT (PCCT) represents a transformative step forward in imaging technology. Unlike conventional energy-integrating CT, PCCT offers a) superior spatial resolution, enabling clearer visualization of tumor margins and fine anatomical structures, b) enhanced tissue characterization, allowing better differentiation between tumor tissues and normal tissue; c) spectral imaging capabilities, facilitating improved dose calculations. These attributes are particularly advantageous in high-precision radiotherapy techniques, such as stereotactic body radiotherapy (SBRT) or proton therapy, where small errors in target delineation or dose delivery can significantly impact treatment outcomes. However, very limited data reporting the clinical use of PCCT for RT planning are available.

Inclusion criteria:

• ≥18 years old patients
• tumors located in challenging anatomical regions (brain, head and neck, liver, pancreas prostate), or Cardiac disease requiring RT by photon or proton at our Institution.

Exclusion criteria:

- 18 years old patients

patients undergoing radiotherapy for orphan cancers, chronic conditions, and anatomically complex regions such as brain, head and neck, thorax, liver, pancreas and pelvis.