What is Radiation Therapy (RT)?

Radiation Therapy (RT) is a form of cancer treatment that uses Ionizing Radiation (strong beams of high-energy particles or waves) to destroy, damage or keep cancer cells from growing and dividing. Radiation Therapy, including intensity modulated radiotherapy, may be used in conjunction with surgery or chemotherapy to treat cancer. Chemotherapy drugs called "radiosensitizers" make cancer cells more sensitive to the radiation, which allows the radiation to better kill cancer cells.

Different types of radiation employed in Radiation Therapy include:

  • X-rays
  • Gamma Rays
  • Proton
  • Electron
  • Neutron

Other names for Radiation Therapy are: radiotherapy, irradiation, therapeutic radiation or x-ray therapy.

What is IR?

The particular type of radiation employed in Radiation Therapy is called "Ionizing Radiation". Ionizing Radiation is radiation with enough energy it can remove tightly bound electrons from the orbit of an atom, causing the atom to become "charged" or "ionized". These ions (electrically charged particles) form in the cells of the tissues it passes through. This can kill cells or change genes so the cancer cells cannot grow, leaving the normal cells to regrow and repair themselves.

Ionizing radiation is ubiquitous in the environment, and also comes from radioactive materials, X-ray tubes, and particle accelerators. It is invisible and not directly detectable by human senses, so instruments such as Geiger counters are usually required to detect its presence. Lower-energy radiation, such as visible light, infrared, microwaves, and radio waves, are not ionizing.

Ionizing radiation occurs in two forms; waves or particles.


Electromagnetic Radiation (e.g. visible light, radio waves) exhibit “wavelike” characteristics in it's interaction with matter (e.g. diffraction patterns, transmission and detection of radio signals). A good way to envision electromagnetic radiation is to describe a wave packet called a photon. Photons are chargeless bundles of energy that travel in a vacuum at the velocity of light, which is 300 000 km/sec.


There are three types of Ionizing Radiation:

  • Indirectly Ionizing
  • Gamma and Xray are types of Indirectly Ionizing radiation. These rays are indirectly ionizing because they are electrically neutral (as are all electromagnetic radiation) and do not interact with atomic electrons through Coulombic forces.

  • Electromagnetic (EMR)
  • EMR has both electric and magnetic field components that oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation and travel through space at the speed of light.

  • Particulate
  • Neutrons are considered directly ionizing because they carry a charge and can interact directly with atomic electrons through Coulombic forces (i.e. like charges repel each other; opposite charges attract each other).

What types of RT are used to treat cancer?

There is a wide range of ionizing radiation energetic particles used in Radiation Therapy. The higher the particle energy, the more deeply the radiation can penetrate the tissues. Also radioactive sources such as cobalt, cesium can be used however these types of radiation therapy aren't used as often in this day and age.

Photon Radiation Therapy

Photon Radiation Therapy is by far the most common type of radiation treatment in use today. X-rays are comprised of photons. Photon radiation uses high energy x-rays to kill cancer cells. A photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation.

Particle Radiation Therapy

Particle radiation is also produced by a linear accelerator. Particle Radiation Therapy is used for tumors close to a body surface. Since these lower energy particles do not go deeply into tissues, they are used to treat superficial and subcutaneous cancers.

  • Protons
  • Protons cause little damage to tissues they pass through but are very good at killing cells at the end of their path. Proton beams may be able to deliver more radiation to the cancer while causing fewer side effects to normal tissues. However proton beam radiation therapy requires highly specialized equipment and is not appropriate for many cancers, that is why proton therapy is currently only offered in certain medical centers.

  • Electrons
  • Neutrons
  • Alpha & Beta Particles

How is RT Administered?

The Radiation Oncologist decides which type of RT is required for you specifically as each type of cancer is somewhat unique. A number of factors are considered when developing a plan to attack your cancer. This plan may include different types and/or combinations of radiation that may prove effective. Radiation therapy can be given in 3 ways:

  • Externally
  • External radiation (or external beam radiation) uses a linear accelerator (LINAC). Most people get external radiation therapy over many weeks, however there are sometimes when there is a shorter course done in a few days or a couple of weeks. Usually this type of radiation is given on an outpatient basis, however in many hospitals, an inpatient can receive their radiation as well.

  • Systemically
  • Systemic radiation is given using radiopharmaceuticals, which are radioactive drugs used to treat certain types of cancer. These drugs are unsealed radioactive sources that can be given by mouth or put into a vein, they then travel throughout the body. Treatment with radiopharmaceuticals often requires a short stay in the hospital.

  • Internally
  • Internal radiation therapy (also called brachytherapy) uses a radioactive source in the form of a wire, seed, pellet, or balloon that is called an implant. The implant is put inside the body in or near the tumor. The radiation from the implant travels only a short distance, so it has very little effect on normal body tissues. In some cases, patients may need to stay in the hospital while getting internal radiation. The implants may either be left in the patient as a permanent implant or they may be removed after a certain amount of time.