Present status of fast neutron therapy in Asian countries.

In Asian countries, fast neutron therapy was first introduced at the National Institute of Radiological Sciences (NIRS), and followed by the Institute of Medical Science (IMS), Tokyo University, and Korea Cancer Center Hospital (KCCH). At NIRS, 2,129 patients were treated with d(30 MeV)+Be neutrons between 1975 and 1994. There were 274 patients referred for the treatment with P(50.5 MeV)+Be neutrons at KCCH during the period of 1986 through 1992. Unfortunately, fast neutron therapy performed at IMS was discontinued in 1991, where 458 patients had been treated with d(14 MeV)+Be neutrons since 1976. At NIRS, a vertical beam with multileaf collimator system was used for treatment of patients referred. The results showed that local control rates were 79% (19/24), 53% (14/26), and 89.3% (50/56) for carcinoma of the salivary gland, osteogenic sarcoma and carcinoma of the prostate, while complications for those were found to be 8.8, 8.3 and 17.8%, respectively. In the treatment of carcinoma of the lung, results were better for patients with adenocarcinoma than those with squamous cell carcinoma. Of 32 patients suffering from Pancoast tumor, 14 achieved local control, whereas 2 of 32 patients developed complications. On the other hand, salvage surgery was required in the treatment of malignant melanoma. In the treatment of malignant glioma, dose localization has to be improved in the target area to confirm local control. Experiences performed at KCCH have shown that, of 53 patients suffering from unresectable primary or recurrent rectal carcinomas, 28 achieved local control. It was concluded from the experiences with fast neutrons in Asian countries that adenocarcinomas as well as slowly growing tumors are indications for fast neutrons and that dose localization has to be improved in order to advance high LET radiation therapy. Clinical trials with 70 MeV protons started at NIRS in 1979, where the aim of study has been focused on treatment of choroidal melanoma, whereas, at Tsukuba University, 250 MeV protons have been used in the treatment of tumors deeply seated. Based on experiences of fast neutrons and protons, clinical trials with heavy ions initiated at NIRS in October 1994. Clinical studies with high LET radiations will be performed by using heavy ions in order to pursue indications of particle radiation therapy.