Radiation Biology Flashcards
Why do we need to understand radiation biology?
- health risk involved with ionizing radiation
- educate the public
- to get licensed as a dentist
- protect the public
How do you measure radiation?
- Exposure Dose; R vs. Coulombs/kg
- Absorbed Dose; RAD vs. Gray (G)
- Equivalent Dose; REM vs. Sievert (Sv)
- Effective Dose; REM vs Sievert (Sv)
What is exposure dose measured in?
- R (roentgen); standard
- air kerma or Coulombs/kg
What is absorbed dose measured in?
- RAD (radiation absorbed dose); standard
- Gray (Gy)
What is equivalent dose measured in?
- REM (Roentgen Equivalent in Man); standard
- Sievert (Sv)
What is effective dose measured in?
- REM (Roentgen Equivalent in Man); standard
- Sievert (Sv)
What is exposure dose?
a measure of the capacity of radiation to ionize air
What is absorbed dose?
energy absorbed by tissue
What is equivalent dose?
modified by radiation weighting factor
What is effective dose?
modified by tissue weight factor
What is 1 RAD (radiation absorbed dose)?
100 ergs or radiation energy in 1 gram of absorbed material
In x-radiation what two types of dose are equal?
equivalent dose
absorbed dose
What is the equivalent dose used for?
To compare the biological effects of different types of radiation
How are absorbed dose and equivalen dose related?
equivalent dose is the absorbed dose times the radiation weighing factor
What does the radiation weighing factor (WR) depend on?
depends on the type and energy of the radiation involved
How many REM are in a Sv?
100 rem = 1.0 Sv
How many RAD are in a Gy?
100 RAD = 1.0 Gy
What is the equation for effective dose?
What is the definition of effective dose?
This measure is used to specifically calculate risks of radiation to human tissues on a common scale
What is the calculation for effective dose?
The calculation is a product of the sum of dose equivalence to the specific tissues or organs exposed and the biological tissue weighting factor
The value of effective dose is an estimated measure of…
all somatic and genetic radiation-induced risk even if the entire body is not uniformly exposed
What is effective dose used for
Used to assess risk of non-uniform radiation to localized part of body and degree to which this would increase a person’s “whole body” risk of
1. cancer induction and/or
2. induction of genetic mutations
What can happen when you expose an object to radiation?
- no interaction = 9%
- coherent scattering = 7%
- photoelectric absorption = 27%
- compton scattering = 57%
What is coherent scattering?
radiation excites the atoms of the biological structure but does not ionize it
What are the two ionizing interactions with objects?
- compton (incoherent) scatter
- photoelectric effect
What type of interaction is this?
Comptom (incoherent) scatter
What type of interaction is this?
photoelectric effect
What kind of injuries can occur from x-ray interactions with matter?
- biochemical lesions that have…
- deterministic effects like lethal DNA damage, cell death, decreased tissue/organ function
- stochastic effects like sub-lethal DNA damage, gene mutation, replication of mutated cells
What are examples of deterministic and stochastic effect from x-radiation injury?
- deterministic (xerostomia, cataracts, osteoradionecrosis)
- stochastic (leukemia, thyroid cancer, salivary gland tumors, heritable disorders)
Ionization from ionizing radiation
exposure sets off multiple direct
and indirect _________ reactions in < 1 sec
molecular
Enzymatic repair or further deleterious molecular changes occur in _____________ after x-radiation exposure
minutes to hours
Deterministic and stochastic effects of x-radiation exposure take place over time from…
months, to decades, to
generations
What happens to x-rays when there is no interaction with the object?
X-ray photon enters object (eg. patient or other biologic tissues) and exits with no change in its energy
What happens when x-rays have a photelectric interaction with an object?
- X-ray photon collides with an orbital electron and loses its energy
- Ejected photoelectron loses it energy
- Results in an atom with an altered electric state, i.e., “+” charge
What percent of all interactions of x-rays are photoelectric interactions?
27-30%
If the degree of photoelectric effect
is significant, this may affect…
biologic structure, function or both
Effects of the photoelectric interaction on biological tissues are…
often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc
What percent of x-ray interactions with objects are compton interaction/scatter?
57-62%
What is a compton interaction/scatter?
- X-ray photon collides with an outer
orbital electron losing some energy - X-ray photon continues in different direction with less energy creating more scatter until all the energy is lost
- results in an atom with an altered
electric state, i.e., “+” charge
What happens during a coherent interaction between x-rays and an object?
X-ray photon of low energy interacts with an outer orbital electron and changes direction
What are the similarities between direct and indirect x-ray injuries?
– Both effects occur quickly
– Both effects take hours to decades to become evident
– Both are a result of ionization
What does direct biologic injury from x-rays do?
➢ Directly ionizes biologic maromolecules
➢ Contributes to about 1/3 of biologic effects
What does indirect biologic injury from x-rays do?
➢ X-ray photons absorbed by H2O → free radicals → biologic damages
➢ Contributes to about 2/3 of biologic effects
What are the three paths that cells can take after direct effect injury?
- repair (cell survival)
- misrepair (carcinogenesis/mutation)
- unrepaired (death)
What is the primary method of cell damage from the indirect effect?
radiolysis of water caused by x-radiation resulting in free radicals
What are free radicals?
a free atom or molecule carrying an unpaired orbital electron in the outer shell
Free radicals seek a more stable
configuration which results in formation of…
toxic substances
- hydrogen peroxide
- H+
- water
What does the threshold non-linear curve of radiation show?
- Small exposures do a substance do not produce measurable changes
- A threshold must be reached before changes are observed
Most biologic effects are linear or non-linear curves?
non-linear
What does the linear non-threshold curve of radiation show?
- Dose is proportional to the response
- No matter how small the dose, there is some damage or risk
What does the non-linear nonthreshold curve of radiation show?
- No threshold
- Minimal damage at first with increased rate of damage with increased dose
What does determinitic risk/effect mean for radiation?
severity is proportional to the dose
- higher does can lead to…
●Erythema
●xerostomia
●cataract
●osteoradionecrosis
●fertility issues
●fetal development
●alopecia
What does stochastic effect mean for radiation?
- Have no dose threshold
- Probability of occurrence is proportional to dose
- Severity of effects does not depend on dose
- To somatic cells -genetic mutations cause malignancy
- To germ cells - genetic mutations cause heritable effects
What type of curve do deterministic effects follow?
threshold - sigmoid
What type of curve do stochastic effects follow?
linear - no threshold
linear - quadratic
What is the difference between a genetic versus somatic radiation injury?
Genetic Injury
– no affect on parent
– affects future generation
Somatic Injury
– affects parent
– no affect on future generation
What is the sequence of radiation injury
- Latent period
- Period of injury
- Recovery period
What is the latent period of radiation injury?
- Time that elapses between exposure and appearance of clinical signs
- May be short or long depending on:
– Total dose
– Dose rate
Shorter latent period of radiation injury if…
– Increased amount of radiation
– Faster dose rate
What happens during the period of injury of radiation injury?
- Cell death
- Changes in cell function
- Breaking or clumping of chromosomes
- Giant cell formation
- Cessation of mitotic activity
- Abnormal mitotic activity
What happens during the recovery period of radiation injury?
- full recovery for a large percentage of individuals from a few weeks up to two years after exposure
- No recovery i.e, death liley at higher does of >1.2 Gy (120 Rads).
What are the factors modifying effects of x-radiation?
- Total dose
- Dose rate
- Oxygen
- Area exposed
- Cell type and function
- Age
As the total dose increases what happens to damage?
more damage
As the dose rate increases what happens to cellular repairs and damage?
decreased cellular repairs
more damage
As the oxygen content increases what happens to radiosensitivity and damage?
increased radiosensitivity
more damage
What is the difference between radiosensitive and radioresistant?
Radiosensitive – young, immature, rapidly growing and dividing, least specialized
Radioresistant – mature, specialized cells
What types of animals are more radiosensitive?
Mammals more sensitive than reptiles, insects, bacteria
What types of cells have an increase radiosensitivity?
- increased mitotic activity
- inceased cell metabolism
- immature cells/not highly specialized
What age are people more at risk for radiation injury?
Pediatric Patients
Why are pediatric patients more at risk for radiation injury?
- Rate of cellular and organ growth puts tissues at greatest level of radiosensitivity
- Greater life expectancy puts children at 2-10 greater risk of being afflicted with a radiation induced cancer
What is acute radiation syndrome?
A collection of signs and symptoms following acute whole-body radiation exposure
How do we know what actue radiation syndrome is?
Information derived from animal experiments, patient therapeutic radiation exposures, atomic bombings and radiation accidents.
What is a sub-lethal exposure of radiation?
< 2 Gy (200 Rads)
What is a lethal exposure of radiation?
2 – 8 Gys (200 to 800 Rads)
What is a supralethal exposure to radiation?
> 8 Gys (800 Rads)
If you have a higher dose or radiation what happens to the latent period and onset of severe symptoms?
shorter latent period and rapid onset of severe symptoms
What are the different categories of acute radiation syndrome?
- Prodromal period
- Hematopoietic syndrome
- Gastrointestinal syndrome
- Central nervous system and cardiovascular syndrome (CNS/CVS syndrome)
How much radiation is the prodromal period?
(<200 R; <2Gy)
How much radiation is the hematopoietic syndrome?
(200- 1,000R; 2-10 Gy)
How much radiation is the gastrointestinal syndrome?
(1,000 – 10,000R; 10 – 100 Gy)
How much radiation is the Central nervous system and cardiovascular syndrome?
(>10,000R; >100 Gy)
When does the prodormal syndrome occur?
Shortly after exposure to whole-body radiation
What are the symptoms of prodormal syndrome?
- nausea
- vomiting
- diarrhea
- anorexia
- general malaise
- fatigue
- drowsiness
- listlessness
How quickly do symptoms of prodormal syndrome resolve?
Symptoms resolve after several weeks
What is the hemopoietic syndrome?
irreversible injury to the proliferative capacity of the spleen and bone marrow with loss of circulating peripheral blood cells
What are the symptoms of hemopoietic syndrome?
- infection from the lymphopenia and granulocytopenia
- hemorrhage from thrombocytopenia
- anemia from the erythrocytopenia
How soon does death occur with hemopoietic syndrome?
10-30 days
What is the gastrointestinal syndrome?
- extensive damage to the GI system (in addition to the hemopoietic system)
- There is extensive injury to the rapidly proliferating basal epithelial cells of the intestinal villi which leads to atrophy and ulceration.
What are the symptoms of gastrointestinal syndrome?
- loss of plasma and electrolytes
- hemorrhage and ulceration
- diarrhea, dehydration, weight loss
- Infection
How soon does death occur with gastrointestinal syndrome?
3-5 days
What is cardiovascular and CNS syndrome?
- radiation induced damage to neurons and fine vasculature of brain
- Intermittent stupor, incoordination, disorientation, and convulsions from extensive CNS damage
How soon does death occur with cardiovascular and CNS syndrome?
death in a few minutes to 48 hours
Oral tissues are subjected to high doses of radiation during the treatment of…
malignant tumors of the soft palate, tonsils, floor of the mouth, nasopharynx, and hypopharynx
Total radiation doses to treat malignant tumors ranges from…
6,000 - 8,000 Rads Or 60 -80 Gy
What is the radiation dose for a solid tumor?
60 – 80 Gy
What is the radiation dose for lymphomas?
20 – 40 Gy
What is the radiation dose for intraoral cancer?
50 Gy
What is the radiation dose for a Full Mouth series?
35 µSv
How many µSv are in 1 Gy?
1 Gy = 1 million µSv
What is the radiation dose for a single intraoral?
1.3 µSv
What is the radiation dose for a panoramic radiograph?
9 µSv
What provides greater tumor destruction: a single large dose or multiple small doses?
Fractionation of the total dose into multiple small doses provides greater tumor destruction
Fractionation of radiation for cancer treatment also increases cellular _________ of the normal tissues
repair
What are the radiation effects on the mucosa?
- mucositis
- secondary infections
What are the radiation effects on the taste buds?
- loss of taste
What are the radiation effects on the salivary glands?
- xerostomia
What are the radiation effects on the teeth?
- lack of or retarded development
- radiation caries
What are the radiation effects on the bone?
osteoradionecrosis
What are the radiation effects on the muscle?
fibrosis
Epithelial atrophy, xerostomia and mucositis all result in _____________ by the 2nd or 3rd week of treatment
loss of taste
Recovery of taste sensitivity will occur in ____ months following treatment
2 - 4
Adult teeth are or are not resistant to the direct effects of radiation exposure
very resistant!
T/F: there is no discernible effect on the crystalline structure of enamel, dentin, or cementum with radiation
True
Radiation does or does not increase the solubility of teeth?
Does not
When teeth are irradiated during the developmental stage, their growth may be severely __________
retarded
If the radiation precedes calcification, the tooth bud may be ___________
destroyed
Irradiation ______ initiation of calcification, teeth may demonstrate malformations and arresting general growth
after
Generally, if some portion of the salivary gland has been spared, the dryness of the mouth subsides in…
6 month to 1 year
_____ salivary glands are often exposed unavoidably to radiation during treatment for carcinoma of the oral cavity or oropharynx
Major
Parenchymal cells (especially of the parotid glands) are very sensitive to X-rays and are replaced by…
fibrosis and adiposis with parenchymal degeneration and loss of fine vasculature
The residual saliva after radiation has a _______ pH, which is acidic enough to initiate decalcification of enamel
lowered (from 6.5 to 5.5)
The buffering capacity of saliva after radiation is reduced _____%
40 - 45%
Children may show defects in the permanent dentition, such as…
- retarded root development
- dwarfed teeth
- failure to form one or more teeth
A dose as low as 200 R at the age of 5 months has been reported to cause __________ of the enamel
hypoplasia
Irradiated teeth with altered root formation will or will not erupt?
will erupt
- eruptive mechanism is much more radiation resistant
A rampant form of decay that may affect individuals who received a course of radiation therapy that include exposure of the ___________
salivary glands
The primary damage to bone is from irradiation to the…
– fine vasculature
– marrow (affecting vascular and hemopoietic elements)
What does inflammation and fibrosis of muscle from radiation cause?
contracture and trismus in the muscles
