Biological effects of Ionizing Radiation - MT1 - 5Qs Flashcards
What is radiosensitivity?
The differences in sensitivity by various tissues according to amount and type of radiation
How does fluoroscopy compare to x-ray radiation?
Fluoroscopy is dynamic (moving) imaging, while x-ray imaging is static
What percent of x-ray units in the united states are dental
~50%
Dental radiographic examination hold what position in terms of greatest number and cost?
2nd (chest radiographs are first)
What are the 2 broad categories of biological effects from radiation?
- Deterministic
2. Stoichastic
Describe the characteristics associated with Stoichastic effects
- No does threshold
- All or non – probability of occurrence of effects is does dependent
- Long-term effects
What are 2 illnesses associated with deterministic effects of radiation?
- Oral mucosal changes
2. Radiation sickness
Describe the characteristics of dose with deterministic effects of radiation
- There is a DOSE THRESHOLD
- Severity of response is proportional to dose
- Acute effects
Are stoichastic effects considered acute or chronic?
Chronic
Are deterministic effects considered acute or chronic?
Acute
What are 2 illnesses commonly associated with stoichastic effects of radiation?
- Radiation-induced cancer
2. Radiation-induced mutations
What is the DIRECT biological effect of radiation with water in the body?
Free Radical Production – leading to dissociation and cross-linking
About what fraction of biological effects are created by direct action of x-ray photons with water in the body?
~1/3 due to direct effects
What is the INDIRECT biological effect of radiation with water in the body?
Radiolysis of Water – produces hydrogen peroxide, hydrogen radical, hydroxyl radical, and hydroperoxyl radicals
About what fraction of biological effects are created by indirect action of x-ray photon with water in the body?
~2/3
Name the 4 biological structures/mechanisms affected by radiation
- Biological molecules
- Cell structures
- Cell cycle
- Tissues and organs
What are the products resulting from radiolysis of water?
Produces free radicals and hydrogen peroxide which is terrible for biological molecules
Describe the consequences of free radical production
Free radicals cause unstable products to be produced and these unstable biological molecules will try to divide further (dissociation), and then these further divided molecules will pick up other biological molecules thus creating highly abnormal molecules within the body (cross-linking)
What are the 6 possible detrimental effects that radiation my have on a cell and the structures within the cell?
- Chromosomal break
- Vacuolization
- Mitotic Changes
- Impaired function
- Recovery
- Cell Death
Is a chromosomal bread worse for single strands or double strands?
Double strands
What is the purpose of vacuolization?
To clear out a cell of debris following severe damage
What are the 2 effects that radiation can have on the cell cycle?
- Mitotic delay
2. Cell Death
What phase of the cell cycle is most sensitive to radiation?
M phase
What 2 phases of the cell cycle are most impacted by mitotic delay?
- G1 (arrest)
2. G2 (block)
What 2 phases of the cell cycle are impacted by cell death following radiation?
G2 and M phases
What are is the correct sequence of cell cycle phase sensitivity from most sensitive to least sensitive?
M > G1 > G2 > S
What are the short-term effects of radiation of tissues and organs dependent upon?
Short-term effects depend on sensitivity of parenchymal cells
What are the long-term effects of radiation of tissues and organs dependent upon?
Long-term effects depend primarily on the extent of damage to the fine vasculature
In terms of radiosensitivity, what are the 5 types/categories of cells?
- Vegetative intermitotic
- Differentiating intermitotic
- Multipotent connective tissue
- Reverting post-mitotic
- Fixed postmitotic
Give an example of vegetative intermitotic cell type and its level of radiosensitivity
These are the most radiosensitive type of cells and include cells from the basal layer of the oral mucosal membrane
Give an example of a reverting postmitotic cell type and its level of sensitivity
Reverting postmitotic cells are fairly radioresistant and include cells of the salivary glands
Do all cell types respond the same to radiation?
NO
List the 5 types of cells according to their relative radiosensitivity
Vegetative > Differentiating > Multipotent > Reverting > Fixed
What type of cells (and give 2 examples) are most radioresistant?
Fixed postmitotic are most resistant and include neurons and muscle cells
What is the “Law of Bergonie and Tribondeau” state?
Cells tend to be radiosensitive based on 3 specific properties:
- High division rate
- Long dividing future
- Are of unspecialized type
Name 5 highly radiosensitive tissues/organs
- Lymphocytes
- Bone marrow
- Testes
- Intestines
- Mucous membranes
What are the acute effects resulting from 100Gy exposure?
Death occurs within hours due to cerebrovascular syndrome (neurological and cardiovascular breakdown)
What are the acute effects of 0.5-3.5 Gy exposure?
Varying degrees of nausea, vomiting, diarrhea, redness of the skin, loss of hair, blisters, and depression of immune system
What are the acute effects of 2-5 Gy exposure?
Death occurs within several weeks after exposure due to hematopoietic syndrome (damage to bone marrow)
What are the acute effects of 1 Gy exposure?
Mild radiation sickness, depressed white blood cell count (prodromal syndrome)
What are the acute effects of 5-12 Gy exposure?
Death occurs within days after exposure due to Gastrointestinal Syndrome (bloody diarrhea, and destruction of intestinal mucosa)
What are the acute effects of 0.25 Gy exposure?
Erythema, blistering and residual smooth, soft, depressed scar
In what units are dental diagnostic images measured in?
uSv (note, 1 Gy = 1 Sv)
How are radiation effects dependent on time?
Effect of radiation is dependent on time because for an equal dose of radiation, those exposed with said amount over a longer period of time will have worse effects
What is the most important somatic effect from x-radiation?
Radiation-induced cancer
Is there a proven link between x-radiation from diagnostic radiology to genetic mutation?
No
What 4 tissues are most highly susceptible to radiation-induced cancer?
- Colon
- Stomach
- Lung
- Bone marrow
Are salivary and thyroid glands highly susceptible to radiation-induced cancer?
No, they have low susceptibility
What are the 3 key points of ALARA?
- No practice shall be adopted unless its introduction produces a positive net benefit
- All exposures shall be kept as low as reasonable achievable (every patient Tx plan is customized)
- The dose equivalent to individuals shall not exceed the limits recommended
What kind of film should be used in practice and why?
If using film, the highest speed of film should be used because it allows for substantial reduction in the radiation required to expose the film
What is the effective dose occupational limit according to NCRP and ICRP?
50mSv
What is the effective dose non-occupational limit according to NCRP vs ICRP?
NCRP = 5 mSv ICRP = 1 mSv
Where does most of the world’s radiation come from?
Radon isotope in the soil
In the last 10 years, what has been the fastest growing contribution the the world’s radiation levels?
CT scans
Is radiation induced carcinogenesis an additive or non-additive effect?
Additive effect
Is there any form of radiation that is 100% safe?
No. All radiation is potentially harmful
What is the correlation between occurrence and dose regarding radiation-induced cancer?
The probability of occurrence of radiation-induced cancer increases with increasing dose
Are children more or less susceptible to radiation vs adults?
Children are more radiosensitive
Approximately how many extra fatal cancers occur per million dental radiographs?
2.5
