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Accelerated reoxygenation of a murine fibrosarcoma after carbon-ion radiation
1Space and Particle Radiation Science Research Group, National Institute of Radiological Sciences, Chiba, Japan. ando@nirs.go.jp
Purpose:
Reoxygenation of a murine tumour after irradiation with carbon ions was investigated and compared to that after gamma-rays.
Materials And Methods:
NFSa fibrosarcoma cells were transplanted into the right hind legs of syngeneic C3H male mice. Conditioning irradiation with either 290 MeV/u carbon ions or 137-Cs gamma-rays was delivered to the tumours at 8 mm diameter. At given times after irradiation the leg tumours, either clamped or not, received test doses of photons. Differences in tumour growth delay between the clamped and non-clamped tumours were interpreted in terms of reoxygenation. A lung-colony assay was used to obtain cell-survival curves.
Results:
The oxygen enhancement ratio in the NFSa tumour for 74 keV microm(-1) carbon ions was 1.6 while that for gamma-rays was 3.4. The NFSa tumours reoxygenated 4 days after 30 Gy of gamma-ray irradiation, but reoxygenated as early as 1 day after 16 Gy of carbon ions. Reoxygenation after gamma-rays shortened to 1 day when the tumours were initially clamped for the conditioning irradiation.
Conclusions:
The fraction of surviving oxic cells in the NFSa tumours is larger after irradiation with carbon ions than with gamma-rays, resulting in accelerated reoxygenation.