Response of cultured mammalian cells to accelerated krypton particles.

One of the more interesting observations made in early studies with heavy ions is that the cross-section of the radiosensitive area in mammalian cells increases with LET of HZE particles. It is not certain, however, whether this radiosensitive area is limited to the nuclear area of cells. The successful acceleration of krypton ions to 8.5 MeV/amu at the HILAC Lawrence Berkeley Laboratory, has provided an opportunity to gain more information on this question. Cultured human kidney cells (T-1), growing in exponential phase, were exposed to 3 MeV/amu krypton particles and their colony-forming ability studied. The survival curve was found to be exponential with a mean lethal dose D0=720 rad. A calculation of the cross-section of the radio-sensitive area from the data obtained gives a value of about 145 micrometers2. Present results suggest that the inactivation cross-section stays about the same for heavy ions that have LET greater than 20,000 MeV cm2 g-1, that the nucleus is the only sensitive site for high LET radiation and that a single hit of a heavy ion with very high LET in the nuclear region of the cell can lead to lethal effects. Such particles are therefore extremely dangerous to proliferating living cells.