22. Accelerated Reoxygenation of a Murine Fibrosarcoma after Carbon Ion Radiation

Koichi Ando, Sachiko Koike, Chisa Oohira, Y. -J. Chen, Kumie Nojima, Soichiro Ando Toru Ohbuchi, Nobuyoshi Kobayashi, Wakako Shimizu and Muneyasu Urano

Keywords: tumor groutth delay, lung colony, carbon ions, LET, OER

Reoxygenation of a murine tumor after irradiation with carbon ions was investigated and compared to that after gamma ray irradiation. NFSa fibrosarcoma cells were transplanted into the right hind legs of syngeneic C3H male mice. Conditioning irradiation of either 290 MeV/u carbon ions or 137-Cs -rays was delivered to the tumors (8 mm diameter). At given times after irradiation, the leg tumors, either clamped or intact received test doses of photons. Difference in tumor growth delay between the clamped and non-clamped tumors were interpreted in terms of reoxygenation. A lung colony assay was used to obtain cell survival curves. The oxygen enhancement ratio of the NFSa tumor for 74 keV/ p m carbon ions was 1.6 while that for -rays was 3.4. The NFSa tumors reoxygenated 4 days after 30 Gy of -ray irradiation, but reoxygenated as early as 1 day after 16 Gy of carbon ions. Reoxygenation after -rays was shortened to 1 day when the tumors were initially clamped for the conditioning irradia tion. We conclude that the fraction of surviving oxic cells in the NFSa tumors would be larger after irradiation with carbon ions than with -rays, resulting in accelerated reoxygenatnon.

Publication:
Ando, K., Koike, S., Oohira, C., Chen, Y. -J., Nojima, K., Ando, S., Ohbuchi, T., Kobayashi, N., Shimizu, W. and Urano, M.: Int. J. Radiat. Biol. 75(4), 505-512, 1999.