Differences in pO₂ peaks of a murine fibrosarcoma between carbon-ion and X-ray irradiation

We measured and compared the oxygen partial pressure (pO₂) profiles in experimental tumors after irradiation with carbon ions and with X-rays. The NFSa fibrosarcomas grown in the hind legs of C3H male mice received isoeffect single doses of carbon ions or X-rays. Coaxial oxygen microelectrodes of high spatial resolution were inserted into the tumor with 20 μm steps by a computerized micromanipulator. The number of pO₂ peaks that reached 15 mmHg were at least 0.45 per 3,000 μm in unirradiated tumors and significantly increased to 1.55 per 3,000 μm as early as day 1 of carbon-ion irradiation (p < 0.001). The tumors that received X-ray irradiation also significantly increased pO₂ peaks, but as late as day 3. The time course of pO₂ peak appearance in the present study coincides with a previous report where reoxygenation was measured by paired growth delay assay. The pO₂ peaks appeared selectively in peripheral regions of X-ray irradiated tumors, but they appeared rather homogeneously in the tumor after carbon-ion irradiation. It is concluded that carbon-ion irradiation reoxygenated the NFSa fibrosarcomas earlier in time and deeper in space than the X-ray irradiation did.