Induction of a bystander chromosomal damage of He-ion microbeams in mammalian cells

We report here a bystander effect in chromosomal damage using He-ion microbeam. Human-hamster hybrid cells were irradiated with a precision He-ion microbeam generated by the Columbia microbeam system. When 20% of the cells were exposed to single He ion, the incidence of cells with chromatid-type breaks detected with the PCC technique was covered wide range from 0 to 6 breaks per cell. In contrast, the distribution showed a mixed two-peak pattern, such as non-exposed and all-cell exposed patterns, under the condition of assuming no bystander effect by treating with an effective inhibitor of cell-cell communication. These findings provide clear evidence that single He-ion irradiated cells can induce bystander chromosomal alterations in neighboring cells not directly hit by He ion

Effects of irradiated medium on chromatid aberrations in mammalian cells using double mylar dishes.

We examined the potential contribution of irradiated medium on the bystander effect using custom made double-mylar stainless steel rings. Exponentially growing Human-hamster hybrid (AL) cells were plated on either one or both sides of double-mylar dishes 2-4 days before irradiation. One side (with or without cells) was irradiated with alpha particles using the track segment mode of a 4 MeV Van de Graaff accelerator at the Radiological Research Accelerator Facilities of Columbia University. Since alpha particles can only traverse a very limited distance, cells plated on the other side of a medium-filled mylar dish will not be irradiated by the alpha particles. The results of chromosomal aberrations on un-irradiated target cells that were attached to the top mylar layer indicate that the number of chromatid-type aberrations was higher when there was a bottom layer of cells in the medium filled chambers than just medium alone. Furthermore, when transferring the medium from these cell-irradiated dishes to fresh AL cultures, chromatid-type aberrations were produced in the un-irradiated fresh cells. In contrast, medium irradiated in the absence of cells had no effect on chromatid aberrations. These results suggest that certain modulating factors secreted from the irradiated cells on the bottom mylar layer into the medium, induce chromatin damage in the un-irradiated, bystander cells

Relative Efficiency of TLD-100 to High Linear Energy Transfer Radiation: Correction to Astronaut Absorbed Dose

Response of thermoluminescent detectors (TLD-100) to high linear energy transfer (LET) particles has been studied using helium, carbon, silicon, and iron ions from the Heavy Ion Medical Accelerator at Chiba (Japan), iron ions from the Brookhaven National Laboratory (NY) Alternate Gradient Synchrotron, and 53, 134, 185, and 232 MeV protons from the Loma Linda accelerator. Using the measured relative (to 137Cs) dose efficiency, and measured LET spectra from a tissue equivalent proportional counter (TEPC) on 20 Space Shuttle flights, and 7 Mir flights, the underestimation of absorbed dose by these detectors has been evaluated. The dose underestimation is between 15-20% depending upon the flight inclination and shielding location. This has been confirmed by direct correlation of measured dose by TEPC and TLD-100 at a low shielded location in the Shuttle mid-deck. A comparison of efficiency- LET data with a compilation of similar data from TLD-700, shows that shapes of the two curves are nearly identical, but that the TLD-100 curve is systematically lower by about 13%, and is the major cause of dose underestimation. These results strongly suggest that TLDs used for crew dose estimation be regularly calibrated using heavy ions