Creation of ¹¹C⁺ ion beam for further acceleration with HIMAC

At National Institute of Radiological Sciences (NIRS), National Institutes for Quantum and Radiological Science and Technology (QST), cancer therapy with the use of a carbon beam has been successfully applied since 1994 by 'HIMAC' (Heavy Ion Medical Accelerator in Chiba). The number of treated patients has been increased to nearly 1000 per year. Meanwhile, several carbon therapy facilities for certain kinds of cancers has been also proposed and constructed in Japan. The radiation treatment with the stable ¹²C ion beam has been well established and application of health insurance has been started from this April. Many patients, however, still suffer from refractory and/or spread-out cancers and wait for better treatments. In order to further advance the capability of carbon radiation therapy, the possibility of precise simultaneous observation of the dose distribution during real treatment with the use of positron emitting radioactive ¹¹C ion and the so-called "OPENPET" has been studied by the "Projectile Fragment" scheme. Its intensity, however, was rather limited (∼10⁵ pps) and a good S/N ratio had not been attained. So as to remedy this situation, the acceleration of radioactive ions created by the "ISOL(Isotope Separator Online)" scheme has been proposed. Radioactive ¹¹C ion beam produced by irradiation of high intensity proton beam from the cyclotron has been proposed. At NIRS, ¹¹C of the amount of about 10¹³ are produced in 20 minutes with the ¹¹B(p, n)¹¹C reaction by irradiation with 18 MeV proton beams onto a solid NaBH₄ target. A ¹¹C beam with an intensity of ∼10⁹ can be provided in each 20 minutes cycle. Recent scheme utilizes irradiation onto a solid target under the vacuum condition. Recently, a beam irradiation system to a solid target at a vertical proton beam line of NIRS930 has been completed. In the present paper, in connection with such recent developments, a mass analysing system to guide the selected ¹¹C⁺ ion beam to the HIMAC and its injector has been studied. (author)