User:MedicalWiki123/sandbox

Radiation exposure
Radiation is a moving form of energy, classified into ionizing and non-ionizing type. Ionizing radiation can further be categorized into electromagnetic radiation (without matter) and particulate radiation. Electromagnetic radiation consists of photons, which can be thought of as energy packets, traveling in the form of a wave. Examples of electromagnetic radiation includes X-rays and gamma rays (see photo "Types of Electromagnetic Radiation"). These types of radiation can easily penetrate body tissues because they have high energy. Radiation exposure is a measure of the ionization of air due to ionizing radiation from photons. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air.

Medical exposure is defined by the International Commission on Radiological Protection as exposure incurred by patients as part of their own medical or dental diagnosis or treatment; by persons, other than those occupationally exposed, knowingly, while voluntarily helping in the support and comfort of patients; and by volunteers in a programme of biomedical research involving their exposure. Common medical tests and treatments involving radiation include X-rays, CT scans, mammography, lung ventilation and perfusion scans, bone scans, cardiac perfusion scan, angiography, radiation therapy, and more. Each type of test carries its own amount of radiation exposure. There are two general categories of adverse health effects caused by radiation exposure: deterministic effects and stochastic effects. Deterministic effects (harmful tissue reactions) are due in large part to the killing/ malfunction of cells following high doses; and stochastic effects involve either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.

This article will discuss the nomenclature of medical radiation, effects of radiation on the embryo and fetus, risk and benefits of using radiation to diagnose and treat disease, how radiologists minimize radiation exposure for patients, and other radiation measurement quantities.

Absorbed dose, dose equivalent, and effective dose
There are special dosimetric quantities used to assess the dose from radiation exposure, which is based on the measure of energy deposited in human tissue and organs. These radiation doses are calculated into radiation risk by taking into account variations in the type of radiation, as well as the varying sensitivity of organs and tissues to ionizing radiation. The absorbed dose is the amount of energy that ionizing radiation deposits in any material that it passes through. The measurement unit of absorbed dose is rad (radiation absorbed dose) or Gray (Gy, International or SI unit).

To measure the biological effects of radiation on human tissues, effective dose or dose equivalent is used. The dose equivalent measures the effective radiation dosage in a specific organ or tissue. The equivalent dose is calculated by the following equation:

Equivalent dose= Absorbed dosage x Tissue weighting factor

Tissue weighting factor reflects the relative sensitivity of each organ to radiation.

The effective dose refers to the radiation risk averaged over the entire body. It is the sum of the equivalent dosage of all exposed organs or tissues. Equivalent dose and effective dose are measured in sieverts (Sv).

Effects on embryo and fetus
Risk of malformation depends on the gestational age, with highest sensitivity occurring during the period of organogenesis. Based on animal data, malformations are induced at a threshold of 100 mGy.

Risk of cancer
Ionizing radiation is known to cause the development of cancer in humans. Our understanding of this comes from observation of cancer incidence in atomic bomb survivors. The Life-Span Study (LSS) is a long-term cohort study of health effects in the Japanese atomic bomb survivors in Hiroshima and Nagasaki. In addition, increased incidence of cancer has been observed in uranium miners, as well as other medical, occupational, and environmental studies. . This includes medical patients exposed to diagnostic or therapeutic doses of radiation, as well as persons exposed to environmental sources of radiation including natural radiation.

Life Span Study: The International Commission on Radiological Protection describes a hypothesis that following radiation exposure in single cells, DNA damage response processes lead to the development of cancer. In recent decades, there have been increased cellular and animal data on radiation tumorigenesis that supports this view. However, there is no data showing the incidence of cancer or heritable effects in the low dose range (below about '''100 mSv). __(citation).''' It is scientifically plausible to assume that the incidence of cancer or heritable effects will rise in direct proportion to an increase in the equivalent dose in the relevant organs and tissues. (65) Thus, the Commission bases recommendations assuming that doses below this threshold of 100 mSv will produce a directly proportionate increase in probability of incurring cancer or heritable effects attributable to radiation. This dose-response model is generally known as ‘linear-non-threshold’ or LNT.

Because of this uncertainty on health effects at low doses, the Commission judges that it is not appropriate, for the purposes of public health planning, to calculate the hypothetical number of cases of cancer or heritable disease that might be associated with very small radiation doses received by large numbers of people over very long periods of time.

sources 65 and 66 page 55

Risk of radiation exposure in everyday US activities versus common medical imaging
For instance, in the United States, people are exposed to average annual background radiation levels of about 3 mSv; exposure from a chest X-ray is about 0.1 mSv, and exposure from a whole-body computerized tomography (CT) scan is about 10 mSv,