How can radiation be a therapy for cancer?
There are various forms of radiation that have different uses and also pose different risks to people.
Diagnostic x-rays have been critical in the medical field for diagnosis of many problems. Doctors have learned how to use the least radiation necessary to make a particular diagnosis. They have also learned to shield sensitive areas of the body, like the thyroid gland and the genitals, from radiation.
Radiation can also cause cell damage, and that is how it is used to treat cancer. Much more intense radiation is focused on the area of the tumor, while trying to protect adjacent normal tissue.
Like chemotherapy, radiation therapy stops the ability of cancer cells to grow and multiply. It is more toxic to those cells that are actively multiplying. Unlike chemotherapy, it does not get into the tissues of the entire body. Areas near the tumor will be affected, but usually recover.
For other cancers, radiation can sometimes be delivered by placing a source of radioactivity into the tumor. That does not work for mesothelioma because it spreads so much around all the surfaces it touches. It is not a discrete, separate tumor.
Radiation therapy is rarely, if ever, used as a primary treatment for mesothelioma. It can be used with other treatments, for example to shrink the size of a tumor before surgery, or to try and kill any remaining tumor cells after surgery.
It can also be used to control symptoms, including pain and shortness of breath, by shrinking the tumor.