Flashcards in ￼DENTAL RADIOGRAPHY and RADIA TION BIOLOGY Deck (29):
what is the unit of radiation? is it for particulate or EMR? does it give us information about energy or ionizing ability of radiation?
￼A. Roentgen (R)
• Measures the exposure (based on the amount of ionization of air molecules produced)
• ONLY for electromagnetic radiation (not particulate)
• NO information about energy or ionizing ability of radiation
what is the Gray (Gy)?
• Measures the amount of energy deposited in the irradiated matter
• Dependent on atomic number of absorber, and the energy of the radiation
what is the Sievert (Sv)?
• A measure of biological effect of the radiation
• e.g. “Equivalent dose” (Sv) = Dose (Gy) x radiation weighting factor
• e.g. “Effective dose” (Sv) = Equivalent dose (Gy) x tissue weighting
what type of radiation has what amount of radiation weighting factor?
photons (e.g. xrays) - radiation weighting factor (W subscript R) 1
electrons - 1
neutrons (5 keV) - 5
high-energy protons - 5
alpha particles - 20
what does radiation weighting factor give to us?
￼...gives an estimate of the ionizing ability of a form of radiation (electromagnetic or particular)
￼For practical purposes, in diagnostic radiology using x rays.......
1R ≈ 0.01 Gy ≈ 0.01 Sv
it would be different if you were exposed to a particular level of gamma radiation, the ratio would change?
where does natural background radiation come from?
1. Cosmic rays
2. Earth’s crust
4. Air - most obvious example is radon gas
5. Building materials
6. Human body
￼NATURAL BACKGROUND RADIATION - appox. 2.4 mSv
TERRESTRIAL 2.0 mSv A. External 0.5 mSv
(soil, building materials)
e.g. wood < concrete < brick
B. Radon gas 1.2 mSv
C. Other internal (ingestion) 0.3 mSv
COSMIC 0.4 mSv
how much dose does diagnostic imaging add in population dose worldwide?
￼Diagnostic imaging may add a population dose (average worldwide) of approximately 2.5 mSv per year
Dental radiology is estimated to contribute no more than
0.01 mSv 0.01/2.5 = 0.04%
what is whole body radiation?
Radiation exposing the entire body. Each unit mass of tissue in the body receives the same amount of radiation.
what is specific area radiation?
Radiation exposing a specific area of the body. Only a limited number of total body cells are exposed to ionizing radiation.
what are the two categories of effects of ionizing radiation on tissue?
• direct effect on biological molecules
• free radical or H2O2 formation from radiolysis of H2O
what are biological molecules affected by ionizing radiation?
4. NUCLEIC ACIDS*
• Damage to DNA primary cause of cell death, genetic mutations, carcinogenesis
what are potential effects at the cellular level?
1. Death from changes to organelles
2. Chromosome aberrations
3. Reproductive death
the extent of possible damage to tissues is influenced by... (4 things)
Extent of possible damage is influenced by:
2. Volume of tissue irradiated
3. Type of tissue
4. Period of time in which dose is received
what is radiosensitivity of cells and tissues related to (two things)?
a. reproductive activity (mitotic rate) – highly radiosensitive cells will have high mitotic rates
b. degree of cellular differentiation – highly radiosensitive cells will be poorly differentiated (e.g. stem cells)
what are some highly radiosensitive cells (2)/organs(4)?
Stem cells (spermatogenic and erythroblastic)
Basal cells of mucous membranes
Bone marrow (not really an organ)
what are intermediate sensitive cells and organs?
Salivary gland cells
Parenchymal cells - liver, kidney, thyroid
Growing cartilage and bone
Lungs, kidney, liver
what are low sensitivity organs and cells?
Striated muscle cells
Squamous epithelial cells Erythrocytes
what are some death risk from activities or factors? what does this mean for dentistry?
TRAVEL: Aircraft, automobile, other motorized vehicles
• EATING: Choking • RECREATIONAL ACTIVITY • WORK
• CLIMBING STAIRS • CROSSING THE STREET • SMOKING
• ALCOHOL CONSUMPTION
• EXPOSURE TO KNOWN CARCINOGENS • HIGH FAT DIET
The estimated risk from dental radiography is SMALL in comparison to numerous other risks that are a common part of everyday life.
what are 4 points regarding the safety of radiography?
1. Does not significantly add to total amount that is normally received from “background”.
2. Few highly radiosensitive tissues in area.
3. Radiosensitive tissues of body (usually) protected.
4. Percentage of body tissue irradiated is small.
Although the risk cannot be assumed to be zero...
the benefit of dental diagnostic and other medical imaging is well recognized.
The BENEFIT / RISK RATIO is high.
what is the effective dose?
Used to estimate the risk in humans. It is the sum of the products of the equivalent dose to each organ or tissue and the “tissue weighting factor”.
what is the tissue weighting factor for tissues or organs?
gonads - 0.08
red bone marrow, lung, colon, breast, stomach - 0.12
thyroid gland, bladder, liver, esophagus - 0.04
skin, brain salivary glands, bone surfaces - 0.01
whole body - 1.00
what does the tissue weighting factor do?
...gives an estimate of the relative sensitivity of an exposed tissue or organ to ionizing radiation
A given dose of radiation to the whole body or to higher sensitivity tissues/ organs will result in a higher EFFECTIVE DOSE than a dose of radiation to a lower sensitivity tissue/ organ
SEE THIS TABLE IN THIS LECTURE ABOUT THIS.
what is the "ALARA" principle/
ALARA is an acronym for As Low As Reasonably Achievable. This is a radiation safety principle for minimizing radiation doses and releases of radioactive materials by employing all reasonable methods. ALARA is not only a sound safety principle, but is a regulatory requirement for all radiation safety programs.
how is patient protected with the x-ray machine?
1. X ray machine
a. x ray output and accuracy of settings
d. type of PID / “cone”
e. “dead man” exposure switch
f. kVp cannot be set <60
g. long focal-film distance
h. type of generator (self-rectified or DC)
what are 6 others ways the patient is protected?
2. Fast film / digital receptor**
3. Film holding devices
4. Protective shielding
- lead apron, thyroid collar
5. Radiographic selection* (Chapter 16)
6. Processing (if using film-based imaging)
radiographs are taken based on...?
history, clinical signs, symptoms
radiographs made should be expected to benefit diagnosis and treatment of patient.
how is protection of operator and office personnel carried out? (5 things)
1. Exposure indicator lights and sound.
2. Design of office.
3. Adequate shielding/barriers OR
stand in a safe place.
4. Do not hold films or be in operatory during exposure.
5. Radiation monitoring?
how is protection of other patients and people int he office carried out?
1. Proper shielding.
2. Parent in room - provide protection.
3. Other considerations in (protection of operator and office personnel).