How do X-rays cause damage
The precise mechanism of how X-rays cause these damaging effects is not yet fully known, but two main mechanisms are thought to be responsible:
- Direct damage to specific targets within the cell
- Indirect damage to the cell as a result of the ionization of water or other molecules within the cell.
Specific targets within the cell, probably the chromosomal DNA or RNA in the nucleus, take a direct hit from an incoming X-ray photon, or an ejected high-energy electron, which breaks the relatively weak bonds between the nucleic acids.
The subsequent chromosomal effects could include:
• Inability to pass on information
• Abnormal replication
• Cell death
• Only temporary damage — the DNA being repaired successfully before further cell division.
If the radiation hits somatic cells, the effects on the DNA (and hence the chromosomes) could result in a radiation-induced malignancy. If the
damage is to reproductive stem cells, the result could be a radiation-induced congenital abnormality.
What actually happens in the cell depends on several factors, including:
• The type and number of nucleic acid bonds that are broken
• The intensity and type of radiation
• The time between exposures
• The ability of the cell to repair the damage
• The stage of the cell’s reproductive cycle when irradiated.
As 75% of each cell consists of water, it is the water molecules that are most likely to be ionized by the incoming X-rays. The effects are shown in
(Figure) which illustrates that the damage to the cell results from the free radicals produced by the ionization process.