| Carbon ion radiotherapy (CIRT) is an advanced, biologically optimized form of particle therapy. As of 2024, over 63,800 patients worldwide have been treated with CIRT. This review comprehensively synthesizes current evidence on the efficacy of CIRT for rare tumors arising in the head and neck region, central nervous system, and soft tissues—particularly in comparison with conventional photon-based radiotherapy. Robust clinical data demonstrate superior local control and survival outcomes with CIRT in spinal chordomas, selected rare head and neck malignancies—including adenoid cystic carcinoma—and mucosal malignant melanoma. Promising early results also support its potential utility in high-grade gliomas. In choroidal melanoma, CIRT appears to offer higher local control and eye preservation rates than photon stereotactic ablative radiotherapy (SABR). For unresectable soft tissue sarcomas, CIRT achieves excellent local tumor control with the added benefit of a significantly shortened treatment course. Collectively, these findings inform evidence-based patient selection for CIRT and provide practical guidance for the clinical implementation and strategic planning of new carbon ion facilities. |
