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How Does Radiation Therapy Work to Treat Cancer?

By Richard Pearlman, M.D, radiation oncologist at Alliance Cancer Care

Whether you or a loved one has been diagnosed with cancer, radiation is likely to play some role in treatment. You are probably wondering what radiation is and how it can be used to treat and cure cancer. In this article, I will explain what radiation is and how it works.

When we talk about radiation, we are usually referring to what is called ionizing radiation. Radiation is just another word for electromagnetic radiation, which describes different types of light. Radio waves, microwaves, light we can see, and X-rays are all types of radiation. What makes them different are their energies. Radio waves have very low energy. X-rays have very high energy and cause electrons to be knocked off nearby atoms. These electrons produce the biological and therapeutic effects of radiation.

At this point, you are probably thinking, “that’s interesting, but how do X-rays damage and kill cancer cells?” That is an excellent question. The electrons produced by X-rays interact with the DNA of the cancer cells. DNA, or deoxyribonucleic acid, is the blueprint of all cells. The DNA tells the cell how to make proteins that are vital to its survival. When a high-energy electron from an x-ray hits the DNA, a break forms due to the damage. The cell may die shortly afterward as a result of damage to the DNA, but more commonly, the cell will continue to function immediately after an x-ray treatment.

Sometimes, we will tell patients that radiation continues to work after treatment. What we mean by this is that the damage caused by the radiation to the cell has already occurred, but the cell has not died yet or the tumor has not shrunk or gone away on imaging yet. It takes time for the effects of radiation to be seen on imaging, which is another topic entirely. When radiation damages DNA, the cell will usually die when it attempts to divide. Cancers grow when cells divide. One cell becomes two cells, and then two cells become four, and then four becomes eight, and so on until billions of cells form a tumor. When cells divide, they have to copy their DNA and properly split it between the two new cells. After damage has occurred to the DNA, when cells attempt to divide, the DNA does not properly separate between the two cells, and the cells die shortly afterward. This process depends on how quickly the cells divide, and it happens over several hours usually.

Now, you might be wondering, “does radiation harm normal cells?” The answer to that question is a little complicated, but it can be broken down into two parts. Firstly, we direct the highest doses of radiation to the cancer to help spare the body’s healthy cells. We achieve this goal through advanced targeting and treatment techniques. Secondly, cells can repair some DNA damage. Cancer cells by their very nature have a decreased ability to repair DNA damage compared to normal cells. That is how they became cancer in the first place. When the DNA of a normal cell is hit by radiation, the damage can sometimes be repaired by the cell. This is primarily why we do daily treatments spread out over several weeks as opposed to delivering the entire treatment at once. By spacing out the treatments, the body’s normal cells can repair DNA damage. The cancer cells lack the proper machinery to repair their own DNA, which makes them more sensitive to radiation. The inability to repair DNA damage helps to improve the therapeutic benefit of radiation while decreasing the side effects of treatment by sparing healthy tissue.

Through advances in physics and biology, we have developed the ability to use radiation to treat and cure several forms of cancer. Radiation is a form of high-energy light that causes DNA damage, which is difficult for cancer cells to repair. DNA is vital to the survival of all cells, and when cancer cells try to divide, the DNA is unable to properly split between the two new cells, causing the cells to die. By precisely targeting the radiation dose at the cancer, we can help spare the body’s normal tissues. Hopefully, you now have a better understanding of how radiation works. If you would like to learn more, please contact our center to speak to one of our radiation oncologists for suggestions for more in-depth sources related to this topic.