if radiation causes cancer, why does radiation therapy stop cancer and not give you more cancer?
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Radiation damages cell DNA, but DNA is most vulnerable while it is being used, and also while DNA is being repaired it is unavailable for use.
Cancer cells tend to grow out of control. The nastiest cancers grow way faster than normal cells. This means they are constantly using their DNA for growth. This makes them more vulnerable to radiation. The idea is to cause enough DNA damage that it won’t be available to support growth, and the tumor cells will run out of resources and die.
This is why radiation side effects are mainly on tissues which are constantly regenerating like the lining of the mouth and throat, intestines and blood.
Radiation is an important risk factor for cancer, because of DNA damage. However, cancer Requires a lot of DNA damage in very specific spots, but not enough to kill the cell. This means that radiation alone won’t do it in one go – the damage will kill the cell. However radiation damage with some repair and time to build up additional damage from aging can do it. You need about 10 – 30 years after radiation for cancer to develop.
So radiotherapy has a high risk of causing cancer later, but that is a lot later if you are treating a cancer which would otherwise kill in a year or two.
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