External Beam Radiation Therapy

Radiation therapy, also known as radiotherapy, is part of the multimodal treatment approach that is standard for the care of mesothelioma and for lung cancer. The other two therapies included in this treatment are surgery and chemotherapy.

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There are several different types of radiation therapy, but the one that is most frequently used is called external beam radiation because it uses a machine outside the body to administer treatment. The machine that is most often used is called a linear accelerator (LINAC).

Photon beams of light are directed at the location of the tumor to damage the cancer cells so they can no longer grow and spread. The photon beams are made up of either gamma rays, which have the highest level of energy, or X-rays, which have slightly less energy.

A radiation oncologist, a physician trained to use radiotherapy to treat cancer, administers the treatment. The course of treatment is usually five days a week over several weeks. It is usually performed on an outpatient basis.

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External Beam Radiotherapy and Mesothelioma

The two most common types of mesothelioma are pleural mesothelioma, which affects the membrane that lines the lungs, and peritoneal mesothelioma, which affects the peritoneum, the layer of tissue that lines the abdomen and covers most of the abdominal organs.

Surgery is the primary treatment for pleural mesothelioma. One of the secondary treatments that would be administered to eliminate cancer cells that were left behind during surgery is radiation.

Administering radiation after pleurectomy/decortication surgery (P/D) is difficult because of the possibility of extensive damage to the lungs, including pneumonitis, an inflammation of the air sacs in the lungs that causes difficulty in breathing.

However, radiotherapy after extrapleural pneumonectomy surgery (EPP) is found to extend survival rates because the photon beams are administered to the cavity where the lung has been removed. This lessens the risk of lung damage to the remaining lung, although pneumonitis remains possible.

Intensity Modulated Radiation Therapy

To help lessen the risk of adverse reactions, a specific type of external beam radiation is being explored called intensity modulated radiation therapy (IMRT). This is a type of treatment that uses linear accelerators that are guided by computers so that they deliver specific doses to a precise area. IMRT conforms to the three-dimensional shape of the tumor by controlling the beam so that it is emitted in multiple small doses. IMRT also permits higher doses to be centralized within the tumor while minimizing the dose to surrounding organs/tissues.

Radiation is found to have limited use in the treatment of peritoneal mesothelioma except as a way of preventing malignant "seeding" of the area where the surgical incision was made. Seeding is a condition in which cancerous cells are dropped into an area when the tumor is removed.

Other uses of radiation in the treatment of mesothelioma include:

  • Administering it before surgery to help shrink the tumor so it is easier to remove
  • Using it for palliative care, that is relieving the symptoms of mesothelioma, especially in Stage IV patients.

Adverse Reactions

The general side effects of external beam radiation therapy include fatigue and a reddening, rash and/or hair loss on the area of skin where the photon beams are aimed. When the treatment is used in combination with chemotherapy, it makes the side effects of chemotherapy worse.

A specific adverse reaction associated with radiation treatment for pleural mesothelioma is possible lung damage that can result in breathing problems and shortness of breath. When the therapy is used to treat peritoneal mesothelioma, the patient may experience nausea, vomiting, diarrhea, and a loss of appetite.

Additional Resources

  1. Intensity Modulated Radiation Therapy. (2011, June 24). RadiologyInfo.org. Retrieved from http://www.radiologyinfo.org/en/info.cfm?pg=imrt
  2. Malignant Mesothelioma. (2012, January 12). American Cancer Society. Retrieved from http://www.cancer.org/Cancer/MalignantMesothelioma/DetailedGuide/malignant-mesothelioma-treating-radiation
  3. Radiation Therapy. (2005, October 21). MedicineNet.com. Retrieved from: http://www.medicinenet.com/radiation_therapy/article.htm
  4. Radiation Therapy for Cancer. (n.d.). National Cancer Institute. Retrieved February 1, 2012, from: http://www.cancer.gov/cancertopics/factsheet/Therapy/radiation

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