Biological Effects Of Radiation Flashcards
Where is most DNA located?
In the cell nucleus
Where are small amounts of DNA found?
In the mitochondria
How many pairs of chromosomes does each cell usually contain?
23 pairs
What are chromosomes made of?
(2)
Proteins
A single DNA molecule
What is the DNA structure?
(4)
2 linked strands to create a double helix.
Each strand has a backbone made of sugar and phosphate groups.
Attached to each sugar is one of 4 bases- adenine, thymine, cytosine and guanine
A+T, C+G
What happens in mitosis?
(7)
The cell begins to divide
The DNA replicates to form 2 copies of each chromosome
The nuclear membrane breaks down.
The chromosomes line up across the centre of the cell
One set of chromosomes is pulled to each end of the cell
The nucleus divides
The cytoplasm and cell membranes divide to form 2 identical cells
What are the 2 stages of the cell cycle?
Interphase
Mitotic phase
What are the 3 stages of interphase?
Gap phase 1 (G1)
Synthesis (S)
Gap phase 2 (G2)
Which stage of the cell cycle is most sensitive to radiation?
Why?
Mitotic phase
Because that’s where the sister cells are being produced
What are the 2 types of radiation damage?
Direct damage
Indirect damage
When does direct radiation damage occur?
When radiation directly damages the DNA, causing either single or double strand breaks
What does direct radiation damage cause?
The breaks in the DNA that it causes, cause disruption to cell replication/duplication
When does indirect radiation damage occur?
It occurs when radiation interacts with non-critical targets within the cell,usually water
What does indirect radiation damage cause?
It causes the production of free radicals which attack other parts of the cell
What are examples of fast growing cells?
(3)
Epithelial cells
Fingernail cells
Hair cells
Are fast or slow growing cells spend more time in mitosis?
Fast growing cells
What is an example of slow growing cells?
Brain cells
What are the consequences of direct radiation damage?
(4)
The cell may be undamaged
The cell may become repaired and work normally
The cell may repair abnormally, where the wrong amino acid bases replace the break, e.g. A+G instead of A+T
The cell may die
What can happen in the cell repairs itself abnormally by the wrong amino acid replacing the break?
This causes cell mutation, so during the next cell division, the abnormality is replicated. This leads to malignancy
During direct radiation damage, where does the radiation hit on the DNA?
(2)
The DNA base
The DNA backbone
During direct radiation damage, what are the 2 types of breaks that can occur?
Single strand break
Double strand break
Which type of radiation damage is more likely to happen?
Why?
Direct radiation damage
Because there’s lots of water in a cell
What % of a cell is water?
90%
What are free radicals?
Atoms or molecules that have an unpaired electron and are highly reactive
What do the free radicals in indirect radiation damage do?
They can attack critical targets, such as the DNA
How does indirect radiation damage work?
(3)
Radiation interacts with DNA
It breaks the water, leaving 2 hydrogens and 1 oxygen- this leaves OH and H+
The H+ is the free radical and it’s looking for an OH to pair with and produce water again
What is the free radical?
H+ (hydrogen atom)
What are photons also known as?
X-rays
Why does radiation lose energy when it interacts with matter?
Because it’s interacting with atoms
What does LET stand for?
Linear
Energy
Transfer
What does the LET (linear energy transfer) do?
It determines the biological consequence that a specific type of radiation causes
What is the linear energy transfer (LET) measured in?
Kiloelectronvolts (KeV) per micrometer
What does the linear energy transfer (LET) depend on?
(2)
The type of radiation
The type of material traveled through
They deposit
What does high LET include?
Particles with a lot of mass and charge
What is an emerging form of cancer treatment for children?
Protons
Why are protons used as an emerging form of cancer treatment for children?
Because they deposit all their energy at the end of their trajectory- making them better than x-rays
Where does low LET come from?
External electromagnetic radiation, such as x-rays
What does high LET include?
Protons
What is the linear energy transfer (LET)?
It measures of the amount of energy that an ionising particle transfers to a material per unit distance
What happens in high LET?
The protons deposit a large amount of energy in a small distance, which can cause a lot of biological damage in a small area
What happens in low LET?
The x-rays penetrate tissues very easily but they deposit energy infrequently. This means that the energy deposits are spread out, so less damaging events can occur in one cell from one x-ray
What are the 3 dose quantities?
Absorbed dose
Equivalent dose
Effective dose
What is the absorbed dose?
Per kg of a person, how much do the tissues absorb the energy produced by radiation? (It varies depending on the radiation type)
Basically, how much of the energy we put in stays inside the person
What is the equivalent dose?
The effect of radiation on human tissue
What does the equivalent dose allow us to do?
It allows us to compare different types of radiation
What is an ODP?
Someone who isn’t wearing lead
What is an effective dose?
The probability of a harmful effect (cancer) depending on the organs/tissues exposed. The radiation and the tissue both have their own weighting factors
What is exposure measured by?
What the radiation does to substances, so the effect that the radiation has on the substance it’s in.
What’s important about the effect that radiation has on the substance it’s in?
The radiation could cause a different effect depending on the substance, e.g. there’s a higher effect in the eyes than in the bones
What is the absorbed dose expressed in?
Gray (Gy)
How many times smaller is a milligray compared to a Gray
1000x smaller
Why is the absorbed dose not a good indicator of likely biological effect?
Because weighting factors need to be applied to find the equivalent dose and the tissue
Why is the absorbed dose not a good indicator of likely biological effect?
Because weighting factors need to be applied to find the equivalent dose and the tissue
Does each type of radiation have the same weighting factor?
No- they all have their own weighting factor
What is the equivalent dose measured in?
Sieverts
How do we work out the equivalent dose?
Radiation weighting factor
X
absorbed dose to organ/tissue
What is the relative biological effectiveness (RBE)?
The ratio of the doses required by the 2 types of radiation to cause the same level of effect.
Does high or low LET cause more damage?
High LET always causes more damage
What do tissue tolerances do?
They tell us how much dose of radiation a tissue can tolerate before the point of no return
Why are protons used in the cancer treatment of children?
Because we can use a lower dose of them to cause more of an effect, so the side effects are easier to overcome
What does anything above the tolerance dose mean?
Any damage can’t be repaired
What does anything below the tolerance dose mean?
Any damage is repairable
What did knowledge about tissue tolerances allow the creation of?
Dose reference levels (DRLs) e.g. doses that certain x-rays shouldn’t exceed, like chest x-rays
Which type of cell are frequently reproducing?
Most sensitive cells, e.g. epithelial cells
Where do we get exposed to radiation?
Everywhere- we’re always exposed to radiation
What do the physical effects of radiation depend on?
The amount of exposure - high dose or low dose
What can significant side effects depend on?
(4)
Internal exposure
External exposure
Local exposure (to a specific body part)
Whole body exposure
What are examples of internal exposure?
(3)
Food
Inhalation
Radiopharmaceuticals
What are examples of external exposure?
(3)
Sun
Ground
Radiation generator
What are examples of external exposure?
(3)
Sun
Ground
Radiation generator
How do we have data on the physical effects of radiation?
Because of radiation disasters, e.g. Chernobyl (1986). The rates of cancer increased and long term effects exist years later
When do deterministic effects only occur?
When the threshold of exposure has been exceeded
When does the severity of deterministic effects increase?
As the absorbed dose increases
What is important about the radiation doses involved in deterministic effects of radiation?
(2)
They’re usually substantial ( a lot)
They’re usually delivered over a short space of time
What are the effects of the deterministic effects of radiation?
(3)
Cataracts
Erythema (skin reddening)
Sterility
What determines the side effects seen in the deterministic effects of radiation?
The dose received
What does the stochastic effects of radiation mean?
There’s only a probability of an effect occurring, so it’s due to chance
What is the threshold dose for the deterministic effects of radiation?
It has to be below where no clinical effect is obseved
What is the threshold dose for the stochastic effects of radiation?
There’s no threshold level for these effects- the risk of an effect occurring increases as the absorbed dose increases
Are the stochastic effects of radiation easy or hard to detect on wide scale?
Why?
Very hard to detect
Because of low dose exposure
What are the effects of the stochastic effects of radiation?
(2)
Cancer
Hereditary effects
Since the stochastic effects of radiation have no threshold dose, what does it mean?
All doses of radiaton have a chance of causing side effects
What 4 things can be caused by deterministic and stochastic effects?
Acute disorders
Fatal disorders
Late-onset disorders
Hereditary effects
What are the 4 points of pregnancy?
Pre-implantation period
Organogenesis period
Early fetal period
Late fetal period
What is the time period of the pre-implantation period?
0-2 weeks after conception
What is the time period of the organogenesis period?
2-8 weeks after conception
What is the time period of the early fetal period?
8-15 weeks after conception
What is the time period of the late fetal period?
15 weeks after conception to delivery
What is the consequence of irradiating a woman at the pre-implantation period of pregnancy?
Miscarriage
What is the consequence of irradiating a women at the organogenesis period of pregnancy?
Dysplasia (malformation)
What is the consequence of irradiating a woman at the early fetal period of pregnancy?
Mental retardation
What are some things we should take into account to prevent deterministic or stochastic effects of radiation when imaging patients?
(3)
Be mindful of the total exposure time, e.g. if the same patch of tissue is constantly being irradiated, the patient is receiving a high dose of radiation overall
Is the patient seeking a 2nd opinion (lying about already going to another hospital?) We can use PACS as they show proof of image, as all x-ray images get uploaded here
Is there an alternative imaging method which uses less radiation?
What are some things we should take into account to prevent deterministic or stochastic effects of radiation when imaging patients?
(3)
Be mindful of the total exposure time, e.g. if the same patch of tissue is constantly being irradiated, the patient is receiving a high dose of radiation overall
Is the patient seeking a 2nd opinion (lying about already going to another hospital?) We can use PACS as they show proof of image, as all x-ray images get uploaded here
Is there an alternative imaging method which uses less radiation?
