Yield of OH near the Bragg peak of heavy-ion beam from HIMAC

Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*

Cancer therapy needs ions of several GeV to attain sufficiently long penetration depth into human body (normally 30 cm) to treat cancer in deep position. While advantages of heavy ion therapy are well-known phenomenologically, details of mechanism in which heavy ion irradiation leads to distinctive biological effectiveness have not been clarified yet. Then, understanding of water radiolysis with heavy ions is necessary because water is main component of human body. Aqueous solution of Coumarin-3-carboxylic acid (CCA) has been applied to yield-measurement of OH produced in water radiolysis with therapeutic carbon ion beam provided from HIMAC at NIRS. Production yield of a fluorescent probe, 7OH-CCA, which is a stable product produced after scavenging reaction for OH by CCA, was determined by using HPLC connected to a fluorometer. By using this chemical system, OH yields near the Bragg peak have been measured. Contribution of fragmentations, which are known to be significant near the Bragg peak of high-energy heavy ions, is also discussed by conducting fragmentation simulation.