In 1994 a Phase I/II clinical study on
carbon ion radiotherapy was begun at NIRS using HIMAC, which was then the world's only heavy ion accelerator complex dedicated to medical use in a hospital environment. Among several types of ion species, we have chosen
carbon ions for
cancer therapy because they had the most optimal properties in terms of possessing, both physically and biologically, the most effective dose-localization in the body. The purpose of the clinical study was to investigate the efficacy of
carbon ion radiotherapy against a variety of
tumors as well as to develop effective techniques for delivering an efficient dose to the
tumor. The RBE of
carbon ions was estimated to be 2.0 to 3.0 along the SOBP for acute skin reactions. As of August 2006, a total of 2,867 patients had been entered into Phase I/II or Phase II studies and analyzed for toxicity and local
tumor response. The results have shown that
carbon ion radiotherapy has the potential ability to provide a sufficient dose to the
tumor with acceptable morbidity in the surrounding normal tissues.
Tumors that appear to respond favorably to
carbon ions include locally advanced
tumors and those with histologically non-squamous cell type of
tumors such as
adenocarcinoma,
adenoid cystic carcinoma,
malignant melanoma,
hepatoma, and bone/
soft tissue sarcoma. By taking advantage of the
biological and physical properties of high-LET radiation, the efficacy of treatment regimens with small fractions in short treatment times has been confirmed for almost all types of
tumors in
carbon ion radiotherapy.