radiation biology lesson #8

if a pt refuses to take radiographs, what can happen?

dentist can refuse treatment

what is the biological tissue damage from radiation in the dental office?

we utilize many percausions to protect the pt and ourselves but there is always a chance of biological tissue

what is risk vs benefit?

is taking a radiograph worth the possible risk to the pt's tissue? we only take the minimum amt of radiographs needed (ex: we don't take FMX if the dentist only needs bitewings)

what is the descending order?

organism -> organ -> cells -> molecules -> atoms

what is the study and science of the effects of radiation on living organisms?

radiation biology

what is the energy (no mass no charge) in an xray?

electromagnetic radiation

what is the type of radiation in an xray that DOES have mass and charge?

particulate radiation

what is the ability of an object to absorb different amounts of radiation based on different thickness and density?

attenuation

what is the transfer of x-ray energy to material or matter?

absorption

what are the factors that affect absorption?

energy of the radiation, structural density, thickness, atomic number

what happens to the energy of an xray as it passes through matter?

gradually loses energy, weakens and disappears, energy is transferred to the matter it passes through, it is either absorbed, scattered, or it passes through, the latent image is produced based on what the xray passed through

what are the three ways that an xray exits the tubehead and arrives at the pt?

absorbed, scattered, or passes through

what are the three ways that the interaction of x-radiation with human tissue occurs at the atomic level through?

ionization or excitation or no effect

what produces ion pairs?

ionization

what is a positive ion?

atom missing an electron, has more protons and neutrons

what is negative ion?

atom gains an electron, more electrons than protons and neutrons

how would a positive ion or negative ion return to a neutral state?

ion combine with other atoms or molecules

what is the addition of energy to a system and changing it from its original state?

excitation

what is this called: xray interactions with matter at the atomic level in body tissues?

direct effects

which direct effect causes NO ionization? why?

classic scattering; electron just sits and vibrates, does not have enough energy to remove an electron

which direct effects allows for ionization to occur?

photoelectric and compton

inner orbiting electron is the one that leaves?

photoelectric effect

outer orbiting electron is the one that leaves?

compton effect

what might the direct effects of photoelectric or compton result in due to possible further molecular interactions in the pt's tissues?

- breaking molecules into smaller pieces

- disrupting molecular bonds

- forming new bonds within molecules

- forming new bonds between molecules

what percentage of radiation induced damage is from direct effects?

33%

what is the effect where molecules can be altered indirectly by ionization of water (radiolysis)?

indirect effect

what does the H2O interection in indirect effects cause?

production of free radicals: atoms or molecules with unpaired electrons that are highly reactive

results in formation of new molecules with different chemical and biological properties

free radicals occurs when xray photon ionizes water

these interactions may destroy the molecule's ability to function normally

does indirect or direct effects account for 66% of induced damage?

indirect effects

what can free radicals in indirect effects combine to form that is a toxin?

hydrogen peroxide

how is damage kept at a minimum in terms of indirect effect?

when H2O2 is broken down, the ions have a strong tendency to recombine immediately to form H2O again, usually will repair by the time the procedure is completed

what organization established radiation measurement?

international commission on radiation units and measurements (ICRU)

what is the measurement of radiation quantity or exposure? refers to the ability of xrays to ionize air (not absorbed by tissue)

exposure dose

what measures the exposure dose?

roentgen (R) and Coulombs per kilogram (C/kg)

what dose is defined as the amt of energy absorbed by the tissue? measurement of energy of any type of ionizing radiation imparted to a mass of any type of matter, but does not take into account the radiosensitivity of the tissue

absorbed dose

what measures the absorbed dose?

radiation absorbed dose (rad) and gray (gy)

how do you convert from rad to gray? 1 rad = ? gray

0.01

how do you convert from gray to rad? 1 Gy = ? rads

100

what measurement is used to compare the biologic effects or damage from different type of radiation? takes into account absorbed dose AND the radiosensitivity of certain tissues?

dose equivalent measurement

what measures the dose equivalent?

Roentgen equivalent man (REM) and Sievert (Sy)

how do you convert from rem to sievert? 1 rem = ? sievert

0.01

how do you convert from sievert to rem? 1 Sv = ? rems

100

what is the preferred unit of measure for comparing the risk of different radiographic examinations and the weight of different tissue? this is used to estimate risk in humans

effective dose

what measures the effective dose?

sieverts only

is there a traditional dose equivalent to effective dose?

no, bc sieverts only

what are tissues in the body assigned a weight based on?

sensitivity to developing cancer and tissue thickness

what represents the dose produced by the xray unit to each individual tissue or organ multiplied by the tissues sensitivity to developing cancer or genetic effects?

effective dose

exposure dose

measures the ionization of air (Roentgen or coulombs/kg)

absorbed dose

measures the amount of radiation actually absorbed by tissue (rad or gray)

dose equivalent

brings all forms of radiation to the same level, used for radiation protection purposes (rem or sievert)

effective dose

the sum of the does equivalent to all organs and the weight of each organ using a specific formula (sievert)

what measures the rate that radiation energy is transferred to the tissue along its path? plots the dose administered to the damage produced

linear energy transfer (LET)

do you want higher or lower LET in terms of tissue damage?

lower LET = less tissue damage

what is the amt of radiation absorbed per unit mass of tissue?

dose

what is the total amount of radiation energy absorbed?

total dose

what is radiation dose delivered over a prd of time? fractioned or given at the same time?

dose rate

the higher the dose rate...

the greater the damage

what is the process of dividing total dose into multiple smaller doses delivered over a prd of time?

fractionation of dose

how is fractionation of dose relevent?

allows for cellular rest and repair between doses enables pt to survive high doses needed to kill tumor cells

what is the dose factor that keeps in mind the volume of tissue exposed?

localized vs whole body dose

what is an example of localized dose?

collimated dental xrays (represents 1% of the total body)

what are all tissues of the body EXCEPT reproductive tissues?

somatic tissues

are somatic effects passed to future generations?

NO, somatic effects are seen only in the person that has been irradiated

what are some negative somatic effects?

cataracts, cancer, leukemia

what somatic effect can be caused by 100 to 300 rads (1-3 gy) localized dose?

oral mucositis

what somatic effect can be caused by 300 to 600 rads (3-6 gy) localized dose?

skin erythema

what is another somatic effect on developing teeth? teeth not developing or roots not formed

teeth alteration

what somatic effect is caused by 5000 to 6000 rads (50-60 gy) fractionated localized dose? non-vital bone in the site of radiation exposure

osteoradionecrosis

what somatic effect can be caused by holding films in pt's mouths?

damaged thumbnail, skin changes

what are effects NOT seen in the person exposed but ARE passed down to future generations? occur only in reproductive cells

genetic effects

somatic effects can be repaired, can genetic effects be repaired?

no

how do genetic effects work?

radiation effect on cells, ionizing radiation may affect the nucleus, the cytoplasm, or the entire cell, damage to the nucleus affects chromosomes containing DNA

the degree to which an organism, tissue, organ, or cell is susceptible to the effects of ionizing radiation?

= high sensitivity

radiosensitivity

the level of ionizing radiation that organisms are able to withstand?

= low sensitivity

radioresistant

what specific part of the body is especially at risk in babies and young children due to high sensitivity risk?

immature thyroid

what are critical organs?

if damaged, diminishes the quality of a person's life

what are considered critical organs?

thyroid gland, bone marrow, skin, lens of eyes

what is the time interval between the radiation exposure and observable biologic effects (depends on the total dose of radiation and the amount of time or rate that it took to receive the dose)?

latent period

what type of latent period occurs when a large amount of radiation is absorbed in a short time? ex: nuclear accident (not applicable to dental exposure)

short-term effect

what type of latent period occurs when small amounts of radiation absorbed repeatedly over a long period? these effect associated with dental exposured are unlikely but not risk free

long-term effects

residual injury without repair from repeated radiation exposure?

cumulative effect

what is MPD?

maximum permisable dose

what is MPD for occupational exposure per year?

50 mSv/year or 5 rem/year

what is radiation exposure encountered in daily life (varies depending on where a person lives)

background radiation

what is the percentage of medical (including dental) contributing to man-made radiation exposure?

18%