Time course of reoxygenation in experimental murine tumors after carbon-beam and X-ray irradiation

We compared the tumor reoxygenation patterns in three different murine tumo r cell lines after X-irradiation with those after carbon-beam irradiation u sing a heavy-ion medical accelerator (HIMAC) system. The tumors of the cell lines SCCVII, SCCVII- variant-1 and EMT6 on the hind legs of mice received local priming irradiation with a carbon-beam (8 Gy, 73 keV/pm in LET, 290 MeV/u, 6 cm SOBP) or X-rays (13 Gy, 250 kVp). After various intervals, the mice were given whole-body test irradiation (16 Gy, 250 kVp X-ray) either i n air or after they were killed. The hypoxic fractions were estimated as th e proportions of the surviving fractions of the tumors in killed mice to th ose in air-breathing mice. In the SCCVII tumors, the hypoxic fractions at 0 .5 h were 50% and 21 % (p < 0.05) after the priming X-irradiation and carbo n-beam irradiation, respectively. In the SCCVII-variant-1 tumors, the hypox ic fractions were 85% and 82% at 0.5 h, 84% and 20% at 12 h (p < 0.01), and 21% and 31% at 24 h after X-ray and after carbon-beam irradiation, respect ively. In the EMT6 tumors, the reoxygenation patterns after X-irradiation a nd carbon-beam irradiation were quite similar. We concluded that the reoxyg enation pattern differed among the three tumor cell lines, and that reoxyge nation tended to occur more rapidly after carbon-beam irradiation than afte r X-irradiation for SCCVII and SCCVII-variant-1 tumors.