In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radiation therapy may be curative in a number of types of cancer if they are localized to one area of the body. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor. Radiation therapy is synergistic with chemotherapy, and has been used before, during, and after chemotherapy in susceptible cancers. The subspecialty of oncology concerned with radiotherapy is called radiation oncology. A physician who practices in this subspecialty is a radiation oncologist.
Tumor hypoxia is the situation where tumor cells have been deprived of oxygen. As a tumor grows, it rapidly outgrows its blood supply, leaving portions of the tumor with regions where the oxygen concentration is significantly lower than in healthy tissues. Hypoxic microenvironements in solid tumors are a result of available oxygen being consumed within 70 to 150 μm of tumour vasculature by rapidly proliferating tumor cells thus limiting the amount of oxygen available to diffuse further into the tumor tissue. In order to support continuous growth and proliferation in challenging hypoxic environments, cancer cells are found to alter their metabolism. Furthermore, hypoxia is known to change cell behavior and is associated with extracellular matrix remodeling and increased migratory and metastatic behavior.
Radiosensitivity is the relative susceptibility of cells, tissues, organs or organisms to the harmful effect of ionizing radiation.
In dosimetry, linear energy transfer (LET) is the amount of energy that an ionizing particle transfers to the material traversed per unit distance. It describes the action of radiation into matter.
Louis Harold Gray FRS was an English physicist who worked mainly on the effects of radiation on biological systems. He was one of the earliest contributors of the field of radiobiology A summary of his work is given below. Amongst many other achievements, he defined a unit of radiation dosage which was later named after him as an SI unit, the gray.
Fast neutron therapy utilizes high energy neutrons typically between 50 and 70 MeV to treat cancer. Most fast neutron therapy beams are produced by reactors, cyclotrons (d+Be) and linear accelerators. Neutron therapy is currently available in Germany, Russia, South Africa and the United States. In the United States, one treatment center is operational, in Seattle, Washington. The Seattle center uses a cyclotron which produces a proton beam impinging upon a beryllium target.
Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials.
Particle therapy is a form of external beam radiotherapy using beams of energetic neutrons, protons, or other heavier positive ions for cancer treatment. The most common type of particle therapy as of August 2021 is proton therapy.
Radiobiology is a field of clinical and basic medical sciences that involves the study of the action of ionizing radiation on living things, especially health effects of radiation. Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis. Its most common impact is the induction of cancer with a latent period of years or decades after exposure. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Controlled doses are used for medical imaging and radiotherapy.
Health threats from cosmic rays are the dangers posed by cosmic rays to astronauts on interplanetary missions or any missions that venture through the Van-Allen Belts or outside the Earth's magnetosphere. They are one of the greatest barriers standing in the way of plans for interplanetary travel by crewed spacecraft, but space radiation health risks also occur for missions in low Earth orbit such as the International Space Station (ISS).
In radiobiology, the relative biological effectiveness is the ratio of biological effectiveness of one type of ionizing radiation relative to another, given the same amount of absorbed energy. The RBE is an empirical value that varies depending on the type of ionizing radiation, the energies involved, the biological effects being considered such as cell death, and the oxygen tension of the tissues or so-called oxygen effect.
Astronauts are exposed to approximately 50-2,000 millisieverts (mSv) while on six-month-duration missions to the International Space Station (ISS), the Moon and beyond. The risk of cancer caused by ionizing radiation is well documented at radiation doses beginning at 100mSv and above.
Studies with protons and HZE nuclei of relative biological effectiveness for molecular, cellular, and tissue endpoints, including tumor induction, demonstrate risk from space radiation exposure. This evidence may be extrapolated to applicable chronic conditions that are found in space and from the heavy ion beams that are used at accelerators.
The NASA Space Radiation Laboratory (NSRL, previously called Booster Applications Facility), is a heavy ion beamline research facility; part of the Collider-Accelerator Department of Brookhaven National Laboratory, located in Upton, New York on Long Island. Its primary mission is to use ion beams (H+to Bi83+) to simulate the cosmic ray radiation fields that are more prominent beyond earth's atmosphere.
Auger therapy is a form of radiation therapy for the treatment of cancer which relies on low-energy electrons to damage cancer cells, rather than the high-energy radiation used in traditional radiation therapy. Similar to other forms of radiation therapy, Auger therapy relies on radiation-induced damage to cancer cells to arrest cell division, stop tumor growth and metastasis and kill cancerous cells. It differs from other types of radiation therapy in that electrons emitted via the Auger effect are released with low kinetic energy. In contrast to traditional α- and β-particle emitters, Auger electron emitters exhibit low cellular toxicity during transit in blood or bone marrow.
Travel outside the Earth's protective atmosphere, magnetosphere, and gravitational field can harm human health, and understanding such harm is essential for successful crewed spaceflight. Potential effects on the central nervous system (CNS) are particularly important. A vigorous ground-based cellular and animal model research program will help quantify the risk to the CNS from space radiation exposure on future long distance space missions and promote the development of optimized countermeasures.
Ionizing radiation can cause biological effects which are passed on to offspring through the epigenome. The effects of radiation on cells has been found to be dependent on the dosage of the radiation, the location of the cell in regards to tissue, and whether the cell is a somatic or germ line cell. Generally, ionizing radiation appears to reduce methylation of DNA in cells.
In biochemistry, the oxygen effect refers to a tendency for increased radiosensitivity of free living cells and organisms in the presence of oxygen than in anoxic or hypoxic conditions, where the oxygen tension is less than 1% of atmospheric pressure.
Catharine West is a British cancer researcher who specialised in radiation biology. She is an emeritus professor at the University of Manchester, where she worked from 2002 until 2022.
Eric J. Hall and Amato J. Giaccia: Radiobiology for the radiologist, Lippincott Williams & Wilkins, 6th Ed., 2006
