10 years' history of heavy ion radiotherapy at the National Institute of Radiological Sciences

In 1994, a clinical study on heavy-ion therapy was begun at National Institute of Radiological Sciences (NIRS) using HIMAC (Heavy-Ion Medical Accelerator in Chiba), which was the world's only heavy ion accelerator complex dedicated to medical use in a hospital environment. Among several types of ion species, carbon ions were chosen for clinical use because they had the most optimal properties in terms of biologically effective dose-localization. The purpose of the clinical study was to investigate the efficacy of carbon ions against a variety of tumors, as well as to develop effective techniques for delivering charged particle beams. The relative biological effectiveness (RBE) of carbon ions was estimated to be 2.0∼3.0 at the spread-out Bragg peak (SOBP) for acute skin reactions. As of February 2004, a total of 1,796 patients were entered in Phase I/II or Phase II trials. Of them, 1,549 patients who had a minimum follow-up of 6 months were analyzed for toxicity and tumor response. The results have shown that carbon ion therapy 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 and soft tissue sarcoma. By using biological properties of high-linear energy transfer (LET) radiations, the efficacy of treatment regimen with small fractions and short treatment times has been confirmed for tumors of the parenchymal (parallel) organs such as the liver and lung as well as other types of tumors including prostate cancer, bone and soft tissue tumor, and head and neck cancer. (author)