Radiation therapy is the use of ionizing radiation to treat a medical condition. Radiation is ionizing if it is energetic enough to split molecular bonds. Contrary to common belief, radiation treatment is not a cautery or "burning out" modality, but is a form of chemical treatment. Ionizing radiation causes a change in the genetic material in a cell rendering the cell incapable of duplication. Chemical changes in body tissues result in both the desired effect and undesired side effects. The most common forms of radiation therapy are external beam treatment, brachytherapy, and radioisotope treatment.

External beam radiation most commonly uses a large machine called a linear accelerator to treat a carefully selected part of a patient with either high-energy x-rays or high-energy electrons. The energy of radiation is described in terms of MeV (million electron volts). One of our linear accelerators produces 6 MeV x-rays, the other 15 MeV x-rays and 5 energies of electrons from 6 MeV to 18 MeV. The electron beams are used when a tumor is close to the surface, as they deliver a high dose close to the surface, which tapers off rapidly at a depth determined by the energy.

Brachytherapy refers to radiation treatments given with radioactive material placed into the patient's body. The term intracavitary treatment is used when radioactive sources are placed into a body cavity; the most common circumstance is the placement of Cs-137 (Cesium 137) sources into a woman's uterus and cervix. Interstitial treatment involves the temporary or permanent placement of sources directly into tissue. Temporary Ir-192 (Iridium 192) implants are commonly used in patients with head and neck cancers. The most common permanent implant is the placement of I-125 (Iodine 125) or Pd-103 (Palladium 103) seeds for the treatment of prostate cancer.

Isotope treatment involves giving the patient radioactive material either as a pill or as an injection. Common uses are the use of I-131 (Iodine 131) for the treatment of hyperthyroidism or thyroid cancer, and the use of Sm-153 (Samarium 153) or Sr-89 (Strontium 89) for patients with breast or prostate cancer which has spread to the bone.

Radioisotopes are radioactive forms of naturally occurring elements. The radioisotopes in common use for radiation treatments are produced either in nuclear reactors or in cyclotrons. The number placed after the atomic symbol (e.g., I-131) refers to the number of neutrons plus protons in the atomic nucleus. The number of protons in the nucleus determines which element is present and the chemical behavior; the number of neutrons determines whether the isotope is stable or will go through a process of radioactive decay to an isotope of another element. The type and intensity of radiation differs, and different radioisotopes are therefore suitable for different applications.

Contact radiotherapy involves the use of low energy radiation for the treatment of early stage rectal cancers. Our office is one of the few in this country to offer this modality of treatment.