Adjuvant radiation therapy is delivered after a cancer is treated with primary therapy. Primary therapy, usually surgery, is first used to remove the canceorus growth or reduce the size of the tumor. Adjuvant therapy follows to destroy any remaining cancer cells in order to prevent recurrence in the same organ or to limit metastasis, or spread, to neighboring tissues.
These therapies tend to be systemic, or widespread throughout the body. Primary therapy specifically targets the tumor site. Radiation can be used as either primary or adjuvant therapy. Adjuvant radiation therapy is often used after primary therapy for breast cancer and prostate cancer.
The radiation damages the deoxyriboneucleic acid (DNA) of the cancer cells, either killing the cancer cells or destroying their ability to grow and divide. The radiation shrinks the tumor when used as primary therapy. When used as adjuvant therapy, radiation kills cancer cells that primary therapy might have left unharmed.
Adjuvant radiation therapy consists of focused gamma rays, X-rays and charged particles directed to the tumor site. Radiation therapy can be delivered externally, that is, from a machine outside the body, or internally from radioactive particles implanted near the tumor. Adjuvant radiation therapy also can be delivered throughout the body using radioactive iodine or other charged substances.
The type of radiation, the dose and the frequency of sessions all depend on the type and severity of the cancer. External radiation is typically delivered in daily sessions. These sessions typically are spread over the course of a few weeks.
Internal radiation, or brachytherapy, consists of small radioactive pellets inserted in or near the tumor. Cancerous cells are destroyed by the radiation that is emitted as the implanted particles break down. The pellets decay completely within a few weeks to a few months. The advantage of internal radiation therapy is that the particles are able to deliver a higher dose of radiation than external beam radiation but without as much damage to healthy cells — thus causing fewer side effects.
Adjuvant radiation therapy is unable to distinguish normal, healthy cells from cancerous cells. Although the therapy might be targeted to the region of the body near the original tumor, the radiation can affect and damage normal cells. Side effects vary depending on the location of the treatment, but the most common side effects include fatigue, nausea and vomiting. Other side effects, such as memory loss, bowel damage or infertility, might occur some time after treatment has ended. In rare cases, adjuvant radiation therapy damages normal cells and creates a new cancerous tumor, called a secondary cancer.