The ‘hit theory’ developed in 1920s to explain the actions
of ionizing radiation on cells and organisms was purely
physical, and its limitation was its inadequacy to address
the contemporary findings such as the oxygen enhancement
of radiobiological damage, and the increased radiosensitivity
of dividing compared to non-dividing cells.
The textbooks written prior to 1970s did not either refer
at all to oxygen as a radiosensitizer, or had mentioned it
only in a passing manner; yet ‘oxygen effect’ was emerging
as the central dogma in radiation biology! The oxygen
effect in radiation biology is highly interdisciplinary
encompassing atomic physics (i.e. interaction of photon
with matter), radiation chemistry (formation of reactive
oxygen species), molecular signalling, gene expression
and genetic alterations in cells (mutation, cancer) or the
cell death (apoptosis, necrosis, mitotic catastrophe, etc.).
Cell death in higher organisms is now recognized as the
precursor of possible error-free cell replacement repair.