Asked by: Odysseus Ray Lopez, US
It’s rather like the way guns can be used to commit crime, or stop it. Radiation causes cancer because its high-energy photons can cause breaks in the DNA strands in your cells. Cells can repair this damage up to a point, but sometimes the repair isn’t perfect and leaves some genes defective. If the break affects one of the many tumour-suppressing genes in your DNA, that cell can become cancerous. But cancer cells are also more vulnerable to radiation than ordinary cells. Part of what makes them cancer cells is their ability to divide rapidly and this normally means that some of the DNA ‘spellcheck’ mechanisms are turned off.
So when a cancer cell suffers a break in a DNA strand, it’s less likely to repair it correctly. Depending where the break occurs, it might either kill the cell outright, or make it reproduce more slowly. Radiation therapy uses a focused beam that is aimed at just the part of the body with the tumour, and the dose is carefully calculated to cause the minimum collateral damage to healthy cells. Even so, radiation therapy does very slightly increase your chances of developing a second cancer.