|Fig. 1: This is Gordon Isaacs, the first person to receive external beam radiotherapy for retinoblastoma. (Source: Wikimedia Commons)|
Cancer has long been identified as one of the top 10 leading causes of death in the world. But something really needs to be done. Thankfully, The American Cancer Society, in their most recent report "Annual Report to the Nation on the Status of Cancer, 1975-2006, Featuring Colorectal Cancer Trends and Impact of Interventions (Risk Factors, Screening, and Treatment) to Reduce Future Rates" has identified that both incidence and death rates from all cancers combined have significantly declined in the most recent time period.  This means that there must have been some sort of treatment for cancer. In this article, I will go in-depth about radiation therapy, a method of treating cancer.
First of all, what is radiation therapy (also known as radiotherapy). At high doses, radiation is used to treat cancer by killing cancerous cells; this stops the cancerous cells from spreading to other parts of the body. At low doses, radiation is used as an x-ray; think of all the times you've had to get an x-ray taken at the dentist or at the doctors when you have broken bones.  Every single time, you have been exposed to low doses of radiation.
So, how does radiation therapy actually work and how is it given? Radiation therapy can be given in two ways: through an external beam or through an internal beam. The external beam is when radiation is directed towards cancer cells from a machine outside of your body. The machine is generally very large and rotates around you. This allows the machine to send radiation to your body from many different directions. External beam radiation therapy is considered a local treatment. What this means is that radiation is aimed at a specific part of your body in an area called the treatment area or treatment port. Luckily, external beam radiation therapy does not make you radioactive, which means you are safe to be around other people.  Fig. 1 to the right is a picture of Gordon Isaacs, the first person to be treated with radiation therapy for retinoblastoma in 1957. Gordon's right eye had to be removed due to cancer, but his left eye just had a localized tumor. Therefore, external beam radiation therapy was perfect and he is now living fine with normal vision in his left eye. The internal beam is when radiation is put inside your body, generally in or near cancer cells. A radiation source can either be placed into your body near the cancer cells through the form of seeds, ribbons, or capsules, or you can received liquid radiation by drinking it, swallowing a pill, or through an IV. Liquid radiation is quite interesting as it travels throughout your entire body to find the cancer cells. Radiation sources can be kept inside your body anywhere from a few minutes to the rest of your life. It all depends on what kind of cancer you have. What makes this different from external beam radiation therapy is that you will actually give off radiation. With this danger, doctors, nurses, and visitors have to take extra precautions while contacting you. 
So how does radiation therapy affect cancerous cells and healthy cells? It's actually a fine line that doctors need to know how to balance. High doses of radiation can cure, stop, or slow the growth of cancer.  High-energy radiation damages the genetic material of cells like your DNA and therefore blocks these cells' ability to divide and proliferate further. However, radiation can also affect nearby healthy cells. Luckily, these healthy cells generally recover after the treatment is over. Healthy cells repair themselves faster and can retain its normal function status after radiation. Cancer cells, on the other hand, are not as efficient in repairing the damages and as a result gets killed. Therefore, it is extremely important to aim radiation at the right part of your body, maximize the radiation dose on cancer cells while minimizing exposure to normal cells. 
© Jessica Xu. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 B. K. Edwards et al., "Annual Report to the Nation on the Status of Cancer, 1975-2006, Featuring Colorectal Cancer Trends and Impact of Interventions (risk Factors, Screening, and Treatment) to Reduce Future Rates," Cancer 116, 544 (2010)
 "Radiation Therapy and You," National Cancer Institute, NIH Publication 12-7157, May 2012.
 R. Baskar et al., "Cancer and Radiation Therapy: Current Advances and Future Directions," Int. J. Med. Sci. 9, 193 (2012).