Radiotherapy

Radiotherapy is "the use of ionizing radiation to treat malignant neoplasms and some benign conditions."

Classification

Radiotherapy can be classified by type of radiation, which includes:

• Electromagnetic (photons)
  • X-ray
  • Gamma ray
• Electrons. Electrons are used for superficial targets as the energy of electrons decreases during penetration of tissues
• Protons. Initial research suggests that proton beams with conformal methods, can increase the accuracy of placement of the radiation. A randomized controlled trial of radiotherapy for prostate cancer found improved response of prostate specific antigen without increased local complications. There is concern that particle accelerators for producing protons are proliferating in American health care prior to adequate study of the their role.

Radiotherapy can be classified by the amount of energy associated with the radiation:

• High-energy radiotherapy is "radiotherapy using high-energy (megavolt or higher) ionizing radiation. Types of radiation include gamma rays, produced by a radioisotope within a teletherapy unit; x-rays, electrons, protons, alpha particles (helium ions) and heavy charged ions, produced by particle acceleration; and neutrons and pi-mesons (pions), produced as secondary particles following bombardment of a target with a primary particle."
• Orthovoltage therapy is x-rays between 150 and 500 kV
• Lower energy x-rays (50 to 150 kV) can be used for superficial therapy.

Radiotherapy can be classified by delivery methods:

• External beam
• Brachytherapy is "a collective term for interstitial, intracavity, and surface radiotherapy. It uses small sealed or partly-sealed sources that may be placed on or near the body surface or within a natural body cavity or implanted directly into the tissues."
• Radioimmunotherapy is "radiotherapy where cytotoxic radionuclides are linked to antibodies in order to deliver toxins directly to tumor targets. Therapy with targeted radiation rather than antibody-targeted toxins (immunotoxins) has the advantage that adjacent tumor cells, which lack the appropriate antigenic determinants, can be destroyed by radiation cross-fire. Radioimmunotherapy is sometimes called targeted radiotherapy, but this latter term can also refer to radionuclides linked to non-immune molecules."

Radiotherapy can be classified by the target of the therapy:

• Hemibody Irradiation
• Whole-body Irradiation
• Lymphatic Irradiation

Computer-assisted radiotherapy

Computer-assisted radiotherapy is the use of "computer systems or programs used in accurate computations for providing radiation dosage treatment to patients." Methods of computer-assisted radiotherapy include:

• Conformal photon-beam therapy
• Intensity-modulated radiotherapy (IMRT)