Accelerated reoxygenation of a murine fibrosarcoma after carbon-ion radiation

Purpose: Reoxygenation of a murine tumour after irradiation with carbon ion s was investigated and compared to that after gamma-rays. Materials and methods: NFSa fibrosarcoma cells were transplanted into the r ight hind legs of syngeneic C3H male mice. Conditioning irradiation with ei ther 290 MeV/u carbon ions or 137-Cs gamma-rays was delivered to the tumour s at 8 mm diameter. At given times after irradiation the leg tumours, eithe r clamped or not, received test doses of photons. Differences in tumour gro wth delay between the clamped and non-clamped tumours were interpreted in t erms of reoxygenation. A lung-colony assay was used to obtain cell-survival curves. Results: The oxygen enhancement ratio in the NFSa tumour For 74keV mu m(-1) carbon ions was 1.6 while that for gamma-rays was 3.4. The NFSa tumours re oxygenated 4 days after 30 Gy of gamma-ray irradiation, but reoxygenated as early as 1 day after 16Gy of carbon ions. Reoxygenation after gamma-rays s hortened to 1 day when the tumours were initially clamped for the condition ing irradiation. Conclusions: The fraction of surviving oxic cells in the NFSa tumours is la rger after irradiation with carbon ions than with gamma-rays, resulting in accelerated reoxygenation.