Reading: Chapter 4

 Radiation Biology is the study of the effects of radiation on living tissue.  X-rays are a form of ionizing radiation. When x-rays strike patient tissues, ionization results.  All ionizing radiations are capable of producing biologic changes in living tissue.

 ATOMS which may affect  MOLECULES which may affect  CELLS which may affect  TISSUES which may affect  ORGANS which may affect  THE WHOLE BODY

 Direct Theory ◦ when radiation interacts with atoms of the DNA molecule, it may affect the ability of a cell to reproduce and survive. ◦ Direct injuries from exposure to ionizing radiation occur infrequently.

 Indirect Theory:  when x-ray photons are absorbed within the water inside a cell it can cause the formation of toxic substances. (water to hydrogen peroxide!)  This can ultimately lead to the destruction of the cell.  Injuries of this type occur frequently because our body cells contain so much water. (70 – 80% water!)

 So…if ALL ionizing radiation is harmful, what level of exposure is considered “acceptable”?  With radiation exposure, a dose-response curve can be used to correlate the: ◦ Response (or damage) to the tissue ◦ With the: ◦ Dose (or amount) of the radiation received

 Turn to page 36 in your books.  With radiation a “linear non-threshold” relationship is seen.  A LINEAR relationship indicates that the response of the tissues is DIRECTLY PROPORTIONAL to the dose level.  A non-threshold relationship indicates that a threshold lose level DOES NOT EXIST for radiation.

 The Latent Period  The Period of Injury  The Recovery Period

 The latent period is defined as the time between exposure to x-rays, and the appearance of radiation damage.  This is the first step in the sequence of radiation injury.

 The latent period can be short or long depending upon: ◦ Total dose of radiation received ◦ The amount of time, or rate, it took to receive the dose.  As you may expect: ◦ The MORE radiation received and ◦ The FASTER the dose rate, ◦ The SHORTER the latent period

 A variety of cell injuries may occur. ◦ Cell death ◦ Changes in cell function ◦ Breaking or clumping of chromosomes ◦ Formation of giant cells ◦ Abnormal cell division or cessation of cell division

 Not all cellular radiation injuries are permanent!  Most damage caused by low-level radiation injury is repaired within the body’s cells!!  Scatter Radiation remains in cells, but the body can slough it off in hours. However, repeated exposure does not allow the body time to adjust.

 The effects of radiation exposure are additive, and unrepaired damage accumulates in the tissues.  The cumulative effects of repeated exposure can lead to health problems. ◦ Cancer ◦ Cataract formation ◦ Birth defects ◦ See table 4-1 at the bottom of page 37.

 Total Dose: ◦ Greater damage with larger amounts of radiation  Dose Rate: ◦ A high dose rate does not allow time for cellular damage to be repaired.  Amount of tissue radiated: ◦ Total body irradiation produces more adverse effects than if small, localized areas of the body are exposed.  Cell sensitivity  Age

 Cell sensitivity: ◦ More damage occurs in cells that are rapidly dividing.  Age: ◦ Children are more susceptible to radiation damage than adults.

 Short Term Effects: high doses of radiation over short periods of time tend to kill cells. ◦ Death ◦ Skin burns (erythemia), peeling, blistering ◦ Hair loss ◦ Sterility ◦ Cataracts  Long Term Effects: low doses of radiation over extended period of time produce chronic, or long-term effects, which may not be observed for many years.

 Somatic Effects:  Occur in all cells of the body except the reproductive cells.  These changes are not passed along to future generations.  They only affect the individual exposed.  Primary consequence is cancer

 Genetic Effects:  Occur in reproductive cells  Are passed along to future generations  These changes do not affect the exposed individual, but are passed along by mutations in offspring.  Genetic damage cannot be repaired

 Tissues and organs vary with their sensitivity to radiation.  Radiosensitive organs include: ◦ Lymphoid tissue (small lymphocyte) ◦ Bone marrow (blood forming tissue) ◦ Testes ◦ Intestines  Radioresistant organs include: ◦ Salivary glands ◦ Kidney ◦ liver

 A critical organ is an organ that, if damaged, would diminish the quality of a person’s life.  In dentistry, some tissues and organs are designated as critical because they are exposed to more radiation than others during dental radiographic procedures.

 The critical organs exposed during dental radiographic procedures include: ◦ Skin ◦ Thyroid gland ◦ Lens of the eye ◦ Bone marrow (aka: blood forming tissue) ◦ Turn to page 41 of your text

Panoramic X-ray Exposure Bite-wing X-ray Exposure

 Currently 2 systems are used  Traditional/Standard System ◦ Roentgen (R) ◦ Radiation absorbed Dose (rad) ◦ Roentgen equivalent (in) man (rem)  SI System ◦ Coulombs/kilogram (C/kg) ◦ Gray (Gy) ◦ Sievert (Sv)

 Roentgen (R)- ◦ This is the traditional unit of exposure. ◦ That is the amount of ionization created in a given volume of air.

 Radiation absorbed dose (rad)  This is the traditional unit of dose  Dose can be defined as the amount of energy absorbed by a tissue.

 Different types of radiation have different effects on tissue.  The dose equivalent measurement is used to compare the biological effects of different types of radiation  In the traditional system, the unit of dose equivalent is roentgen equivalent (in) man or rem.

 Radiation can come from 2 sources: ◦ Natural Background Radiation: this radiation comes from the sun, earth, and atmosphere ◦ Artificial Radiation: (man-made) medical/dental x- rays, nuclear, consumer products

Smoke detectors that use “americium”-241 Lawn fertilizer containing potassium-40 Cigarettes Gas lanterns Exit signs Natural gas appliances Brick or stone houses Color television sets

 Radiation is harmful to living tissue.  Because biological damage results from x-ray exposure, dental radiographs should be prescribed ONLY WHEN the benefit of disease detection outweighs the risk of biologic damage.  When dental x-rays are properly prescribed and exposed, the benefit far outweighs the risk.

 Pros  Can help to detect: ◦ Caries ◦ Cysts ◦ Tooth abscess/infection ◦ Retained Roots/Foreign Bodies ◦ Periodontal Disease ◦ Foreign Bodies ◦ Growth Irregularities ◦ Tooth Development ◦ Tooth impactions  Cons  Tissues that can be effected by radiation: ◦ Embryonic tissue ◦ Blood and bone marrow ◦ Skin ◦ Connective tissue ◦ Nerve ◦ Brain ◦ Muscle cells ◦ Enamel

 The ADA sets guidelines for how frequently patients should have radiographs taken based on many factors.  We will discuss these in the next section of this course on “Radiation Protection”.