31 Neoplasms – Radiation Therapy

Radiation Therapy

Radiation therapy delivers a high dose of ionizing radiation directly to the tumor in order to destroy cancer cells by damaging their DNA.  DNA is damaged by the high-energy particles and photons emitted by the radiation itself, as well as by the free radicals that are created within the cell.  Cancerous cells are sensitive to radiation due to their constant state of cell cycling and proliferation.  Radiation therapy is often combined with surgery as it can shrink the tumor making it more accessible for surgery.  Additionally, because radiation therapy is very targeted to one area of the body, it works well when used in combination with chemotherapy.  Chemotherapy is better able to eliminate cells that have migrated away from the primary tumor and that may be missed by radiation therapy or surgery.  Other combinations of therapies are also useful and depend on the type of cancer.  It has been found that some types of cancer cells are very radio-sensitive and are easily killed by radiation, whereas other types of cancer cells are radioresistant and higher dosages of radiation are required.  The term adjuvant therapy refers to therapies that are used after primary treatments to lessen the chance of recurrence.

Delivery Methods of Radiation Therapy

There are many ways to deliver radiation therapy, which include external beam radiation, brachytherapy, radionuclide injections and solutions.

External beam radiation involves using a machine that emits high-dose x-rays or other form of ionizing radiation beam (e.g., gamma rays, proton beam) in a manner that is directed by a 3D image map that has been created of the tumor using MRI, CT scans, and/or PET scans.  Often there is a platform to support the patient in a position that allows the beam to rotate around the patient continually striking the tumor with the beam, while changing its entry point to minimize damage to the skin and surrounding tissues.  If the beam didn’t rotate and continually entered the body from one position, all of the healthy cells along the beam’s path to the tumor would be severely injured.  Sessions often last 30-90 minutes.

Brachytherapy delivers radiation to the body directly, often packaging radionuclides in a ‘seed’ that is implanted directly into the tumor or area that contained the tumor before being surgically removed. The insertion of the radioactive seed is guided by imaging (e.g., ultrasound or CT scan).  Most often any incisions required are small, as the seed can be put in place using a thin wire applicator or catheter.  Unlike external beam radiation therapy, the patient is radioactive while the seed is in place, and will need to stay in a private hospital room (days to weeks) until the treatment is complete and radioactive seed is removed.  Brachytherapy is often used to treat prostate, endometrial (uterine) or cervical tumors.

Radionuclide Injections are used to deliver radiation to specific areas of the body.  For example, the peritoneal body cavity may be injected radioactive gold salts to target cancers that have spread in that region.  Bone cancer that has metastasized can be targeted by using intravenous delivery of specific radionuclides that are preferentially taken up by bone.

Radionuclide Ingestion in which a solid (i.e., capsule) or liquid (i.e. drink or injection) form of radioactive iodine (I-131) is administered for thyroid cancer.  As the thyroid preferentially takes up iodine, the thyroid cancer can be treated while minimizing exposure of radiation to the rest of the body.

Benefits and Potential Adverse Side-Effects of Radiation Therapy

There are many potential benefits as well adverse side-effects of radiation therapy.

Potential benefits of radiation therapy include eliminating tumors from the body which can not only potentially cure cancer, but also eliminate any problems the tumor was creating.  The tumor may have been causing pain, obstruction, damage to surrounding tissues, and loss of function of surrounding tissues.  Radiation can help to shrink a tumor making it easier to remove surgically.  At times, radiation can damage blood vessels supplying the tumor which is also beneficial.

Adverse side-effects of radiation can be both local and systemic. Systemic effects can include fatigue.  Local effects most often relate to damage caused to nearby healthy cells.  For example, signs of inflammation (i.e., swelling, pain, warmth, redness, temporary loss of function).  If the digestive system or pelvis is impacted, symptoms can include nausea, vomiting, diarrhea, loss of appetite (contributing to fatigue), ulcers, gastric bleeding, urinary problems, sexual problems and infertility.  If the brain, head or upper torso is affected by radiation, headache, hair loss, memory and cognitive difficulties, nausea, vomiting, taste changes, dry mouth, stomatitis (inflammation of the mouth), trouble swallowing, cough and dyspnea may occur.   Any internal scarring may cause adhesions or obstructions.  Additionally, external beam radiation therapy can cause skin irritation at points of entry.  As mitotic cells that turn over more rapidly in the body are affected, there may be a decrease in white blood cells, red blood cells and platelets, which can lead to risk of infection, fatigue, and prolonged bleeding.  Similarly, other naturally mitotically-active cells such as epithelial cells can also be affected.  For example, epithelial cells of the skin, hair, and mucosal linings of the respiratory and digestive systems may be negatively impacted by radiation therapy leading to changes in skin, hair loss, and contribute to respiratory and GI problems (e.g., nausea, vomiting, taste changes, dry mouth, trouble swallowing, cough and dyspnea).