Exam Content Category Outline #2 by Destiny Moore

SI Units of Measurement

destinymoore627 — 2022-02-13 01:08:43 UTC

absorbed dose: the measure of energy that is deposited into a medium by ionizing radiation
- Unit of measure is the Gray (Gy)
dose equivalent: the absorbed dose of tissue multiplied by its radiation weighting factor
- Expressed as EqD = D x WR
  - where D = absorbed dose
- Unit of measure is the Sievert (Sv)
exposure: the amount of ionizing radiation in air
- Unit of measure is Coulombs/kilogram
effective dose: the sum of the weighted equivalent doses for all irradiated tissues or organs.
- Expressed as EfD = D x (WR) x (WT)
  - where D = absorbed dose
- Unit of measure is the Sievert (Sv)
air kerma: the concentration of radiation exposure at the surface of the body
- Acronym: Kinetic Energy Released in Matter
- Unit of measure is (Joules/kilogram)^2 (same as Gray)

Radiosensitivity

destinymoore627 — 2022-02-13 01:09:03 UTC

Dose-response Relationships
- Non-linear, threshold
  - there is no bodily response to radiation until a certain dose level is reached
  - beyond that level, the response becomes more effective until it reaches the inflection point
  - the inflection point demonstrates at what dose cells/tissues/organs alter their response; this causes the curve to take on a non-linear shape
- Non-linear, non-threshold
  - a bodily response can be elicited at any amount of radiation
  - the elicited response becomes more effective until the inflection point, the point at which cells/tissues/organs alter their response to the radiation causing the curve to take on a non-linear shape
  - example: when cells start dying off, the maximum damage is done so the response curve decreases
- Linear, threshold
  - there is no bodily response to radiation until a certain dose level is reached
  - beyond that level, the response becomes more effective until it reaches the inflection point
  - as dose increases, biologic response increases
  - characterized by deterministic effects (health effects, the severity of which varies with the dose and for which a threshold is believed to exist. The severity of these effects, rather than probability, increases with dose)
- Linear, non-threshold
  - a bodily response can be elicited at any amount of radiation
  - as dose increases, biologic response increases
  - characterized by stochastic effects (health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold)
Relative Tissue Radiosensitivities
- Linear Energy Transfer (LET): is the average (radiation) energy deposited per unit path length along the track of an
  - High LET: more likely to produce biological damage in a given volume of tissue due to its direct effect/hits
    - Does not travel far in tissue
    - Particulate radiation (alpha particles, low energy neutrons)
  - Low LET: less likely to produce tissue damage in the same volume of tissue by creating free radicals through indirect effect/hits
    - Travels far in tissue and is highly penetrating
    - More damaging in highly oxygenated tissues
    - EM radiation (x-ray and gamma rays)
Relative Biologic Effectiveness (RBE): the principle that biologic damage increases with increasing LET
- Identical doses of both high LET and low LET will not produce the same biologic effect
Cell Survival and Recovery (LD50)
- Lethal dose (LD) 50/30 is a whole body dose that is lethal to 50% of the exposed population within 30 days
  - <3-4 Gy = human survival
  - >6 Gy = 100% death rate without medical intervention
  - >10 Gy = 100% death rate no matter what medical intervention
- LD 50/60 (whole body dose that is lethal to 50% of the exposed population within 60 days) is considered to be more accurate

Somatic Effects

destinymoore627 — 2022-02-13 01:09:21 UTC

Short-term VS Long-term Effects
- Short-term: Expected effects after high acute radiation exposure
  - Effects are typically seen at the cellular level
  - Can either kill or damage the cell
  - Damage to the chromosomes of the cell can impair or destroy the cell's reproductive ability
- Long-term: Damage to cells that are continually reproducing
  - Continually reproducing cells are the most sensitive to radiation because any changes made in the parent cell's chromosome structure will be transmitted to its daughters (Law of Bergonie and Tribondeau)
  - Result is an increasing number of cells that have no beneficial function to the body, yet are absorbing body nutrition at an increasing rate
  - Example: cancer and cataracts
Acute VS Chronic Effects
- Acute: an exposure that is delivered in a short period of time (ex: within a day)
- Chronic: an exposure that continues over long periods of time (ex: months or years)
Carcinogenesis: the initiation of cancer formation; a stochastic effect of ionizing radiation with a linear, non-threshold response.
Organ & Tissue Response
- The Law of Bergonie & Tribondeau: a theory proposed in 1906 stating that cell/tissue radiosensitivity is dependent on four characteristics
  1. Age: younger cells are more radiosensitive than older ones
  2. Differentiation: simple cells without specific functions are more sensitive than complex, high functioning cells
  3. Metabolic rate: cells that use energy more rapidly are more sensitive
  4. Mitotic rate: cells that divide and multiply rapidly are more sensitive
- Example: Lymphocytes are very radiosensitive because they are young cells, have simple functions, use more energy and regenerate quickly; neurons, however, are highly radioresistant because they are older cells, have high complex functions, have lower metabolic rates, and do not reproduce

Acute Radiation Syndromes

destinymoore627 — 2022-02-13 01:09:45 UTC

Four stages of ARS:
- Prodromal period/syndrome:
  - Acute clinical symptoms within hours of exposure
  - Can last a few hours to days
  - Severity of symptoms depends on dose received
- Latent Period:
  - Apparent well being after initial sickness of prodromal period
  - Can last hours to weeks
  - No signs of radiation sickness
  - Precursor to next phase
- Manifest Illness:
  - Reappearance of symptoms
  - Symptoms include apathy, confusion, decreased number of WBC, RBC, and platelets, dehydration, epilation, exhaustion, diarrhea, fever, headache, infection, hemorrhage, cardiovascular collapse
  - Severity of symptoms depend on dose received
- Recovery or Death
  - the exposed person(s) either begin to recover or decline until death
Hemopoietic Syndrome:
- 1-10 Gy whole body dose
- Mild prodromal period (begins within hours and can last several days)
- Latent period can last four weeks
  - General feeling of well being
  - Blood count drops
- Manifest illness symptoms include vomiting, mild diarrhea, malaise, lethargy, and fever
- Non-lethal dose, recovery begins within 2-4 weeks with full recovery in 6 months
Gastrointestinal (GI) Syndrome:
- 6-10 whole body dose
- Prodromal period starts within hours, lasts up to 1 day; symptoms include vomiting and diarrhea
- Latent period can last 3-5 days
- Manifest illness is characterized by second wave of nausea and vomiting, diarrhea, loss of appetite, lethargy, fever, GI bleeding; diarrhea then worsens from loose to watery to bloody as symptoms progress
- Death within 3-10 days post exposure
- Radiation kills intestinal stem cells faster than they are able to renew
Central Nervous System (CNS) Syndrome:
- 50 Gy or more
- Prodromal occurs within minutes with severe nausea and vomiting, nervousness, confusion, burning sensation on skin, loss of vision, loss of consciousness within an hour
- Latent period can last up to 12 hours
- Symptoms return with greater severity during manifest illness; additional symptoms include disorientation, loss of muscle coordination, difficulty breathing, seizures, loss of equilibrium, ataxia, lethargy, coma
- Death occurs within hours to 3 days
- No amount of medical intervention will save the exposed victim
- Inflammation of cerebral blood vessels leads to fluid leakage into brain causing increased intracranial pressure and/or meningitis

Embryonic and Fetal Risks

destinymoore627 — 2022-02-13 01:10:00 UTC

Developing fetuses and embryo are extremely radiosensitive
Radiation to either can potentially cause:
- growth impairment
- prenatal or neonatal death
- congenital malformations
- intellectual disabilities
A dose of 0.1 Gy to the embryo and fetus is recommended as a threshold dose

Genetic Impact

destinymoore627 — 2022-02-13 01:10:15 UTC

Genetically Significant Dose
- a way of comparing and evaluating the genetic impact of various sources of radiation and its effects
- It combines the frequency of radiological examinations obtained during the country-wide survey and estimates of gonadal doses for different examination types, together with population and child expectancy data
Gonadal Shielding
- The National Council on Radiation Protection (NCRP) has concluded that in most circumstances gonadal shielding use does not contribute significantly to reducing risks from exposure and may have the unintended consequences of increased exposure and loss of valuable diagnostic information, and therefore is not justified as a routine part of radiological protection. The NCRP now recommends that gonadal shielding not be used routinely during abdominal and pelvic radiography, and that federal, state, and local regulations and guidance should be revised to remove any actual or implied requirement for routine gonadal shielding.

Definitions

destinymoore627 — 2022-02-13 01:16:49 UTC

References

destinymoore627 — 2022-02-15 15:55:22 UTC

https://www.nrc.gov/docs/ML1117/ML111711087.pdf
https://radiopaedia.org/articles/linear-energy-transfer?lang=us
https://radiopaedia.org/articles/acute-radiation-syndrome?lang=us#:~:text=In%20the%20hematopoietic%20syndrome%2C%20white,predisposes%20to%20bleeding%20and%20perforation.
https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/09.pdf
https://documents.manchester.ac.uk/display.aspx?DocID=26898#:~:text=Short%2Dterm%20somatic%20effects%20are,%2C%20i.e.%2C%20months%2Fyears.
https://radiopaedia.org/articles/radiation-induced-carcinogenesis?lang=us
https://ncrponline.org/wp-content/themes/ncrp/PDFs/Statement13.pdf
https://pubs.rsna.org/doi/10.1148/90.2.209
https://pubmed.ncbi.nlm.nih.gov/9525414/
https://pubmed.ncbi.nlm.nih.gov/11519304/#:~:text=The%20developing%20embryo%20and%20fetus,congenital%20malformations%20and%20mental%20retardation.
https://www.radiologyinfo.org/en/info/safety-xray

Takeaways & Notable Facts

destinymoore627 — 2022-02-17 03:23:54 UTC

Dose

Primary source of background radiation is from radon
- Radon is a naturally occurring gas in the atmosphere that can be trapped in homes
- Often leads to lung cancer
Primary source of occupational dose to technologists is from scatter that is emitted from the patient
- Best practice to reduce occupational dose is with time, distance, and shielding
  - Time: limiting the amount of time the radiographer is in the immediate vicinity of a live x-ray beam
  - Distance: maximizing the distance between the radiographer and x-ray beam whenever possible
  - Shielding: wear protective lead shielding when working within the vicinity of a live x-ray beam

Radiosensitivity

Deterministic effects have a proportional relationship with radiation; as dose increases, so do the severity of effects
- Example: erythema
Stochastic effects are an all or nothing principle; as dose increases the probability that an effect will occur increases, however, the severity of the effect is unchanged
- Example: cancer, you either get cancer or you don't

destinymoore627 — 2022-02-17 03:51:39 UTC

destinymoore627 — 2022-02-17 03:53:25 UTC

Chernobyl - 1986

destinymoore627 — 2022-02-17 04:08:38 UTC

Chernobyl, the nuclear power plant disaster that occurred in Ukraine in 1986, is one of the most well known examples of the effects of acute radiation syndrome. Many citizens of Ukraine exhibited characteristics of all three syndromes. Many people are still suffering the effects of this disaster and, to this day, many objects within the area are still contaminated with radioactivity.

destinymoore627 — 2022-02-17 04:12:44 UTC

Erythema

destinymoore627 — 2022-02-17 04:14:11 UTC

A deterministic effect - exposure of the skin to high doses of ionizing radiation leads to accumulation of lymphocytes in the layers of the skin caused by the effects of cell death and eventually to the development of erythematous skin changes

destinymoore627 — 2022-02-17 04:17:14 UTC