Recently,Histone H2AX phosphorylation on a serine four residues from the carboxylterminus (producing γH2AX) as an ultra-sensitive indicator of the presence of DSBs (sensitive even at the mGy level) has largely supplanted physical methods for the detection of DSBs[1].Analysis of γH2AX has potential to provide useful information on tumor and normal cell response to ionizing radiation after exposure to clinically relevant doses of radiation[2]. Recently, Histone H2AX phosphorylation on a serine four residues from the carboxylterminus (producing γH2AX) as an ultra-sensitive indicator of the presence of DSBs (sensitive even at the mGy level) has been largely supplanted physical methods for the detection of DSBs[1]. Analysis of γH2AX has potential to provide useful information on tumor and normal cell response to ionizing radiation after exposure to clinically relevant doses of radiation[2].