Janae, of Hamilton, asks :-

I am curious about how radiation causes cancer, yet also cures it?

John Le Heron, a Radiation Protection Specialistat the International Atomic Energy Agency in Vienna, Austria, responded.

Because we are bathed in radiation from cosmic rays and the environment the human body evolved to deal with radiation.

Ionising radiations (x-rays, gamma rays, beta particles, alpha particles, neutrons etc) can cause cancer by their ability to damage the DNA in a cell. The damaged DNA is either repaired (in which case there are no consequences) or is unable to be repaired or is mis-repaired, giving a change to the DNA code. With the latter two, the cell usually fails to divide successfully and the cell dies. The loss of small numbers of cells in this way is of no real consequence.

Tissues and organs in the body are designed to cope with cell loss. There are a small number of mis-repairs that still allow the cell to divide successfully, producing daughters that carry the same changed DNA code. These daughters in turn can divide successfully. It is thought that the changed DNA code in some of these cases can lay the basis for a future cancer. Several other factors and conditions typically must occur before this damage has any chance of ultimately leading to a cancer.

As said above, the damage to a cell can cause it to die. By using very large doses of radiation, large numbers of cells can be killed. This approach is used in treating cancer with radiation - cancer cells are killed by giving them a high dose of radiation. The real problem is how to restrict the radiation dose to just the cancer, avoiding the healthy tissue adjacent to the tumour. Another problem is ensuring all the cancer cells receive a high dose. When patients are treated in radiotherapy, the clinicians and physicists try to maximise the cancer dose and minimise the healthy tissue dose by utilising clever ways of delivering the radiation.

More information can be found at our web site: http://www.nrl.moh.govt.nz