Radiation Biology and Protection Flashcards
What is radiobiology?
Study of the effects of ionizing radiation on living systems
Initial interation between ionizing radiation and matter occurs at the level of electro within how many seconds after exposure?
10 to the -13 seconds
Do all x-rays pass through the patient to get to the receptor?
No
What are the two possible effects of some x-rays being absorbed into patient’s tissue?
- Ionization
- Free radical formation
Where is DNA located?
Nucleus
DNA function?
- Control cell
- Contains hereditary information
What is the radiosensitive target molecule?
DNA
What part of the cell cycle is most radiosensitive?
- Mitosis
- G2 phase
What part of the cell cycle is least radiosensitive?
- G1 phase
- S DNA synthesis period
What are the direct biological effects of x-ray exposure?
If radiation is absorbed into biological material, it can interact with the critical target of the cell, leads to biological change
Approximately one third of biological effects are from indirect or direct effects?
Direct
What are indirect effects of x-rays?
Radiation may interact with other atoms or molecules in the cells, especially water, to produce free radicals
What are free radicals?
Atom or molecule carrying an unpaired orbital electron
Free radicals have the ability to…
Diffuse and reach far enough to damage the critical structures in the targets or cell
What are three ways free radicals achieve stability?
- Recombine without causing changes to biological molecules
- Combine with other free radicals to produce chemical changes
- Combine to produce toxins, H2O2
What are deterministic effects?
Killing of large number of cells
What are stochastic effects?
Sub-lethal damage to the cell genome
What are some examples of deterministic effects?
- Lethal DNA damage
- Cell death
- Reduced in tissue and organ function
What are some diseases that are caused by deterministic effects?
- Xerostomia
- Cataracts
- Decreased fetal development
What are some examples of stochastic effects?
- Sub-lethal DNA damage
- Gene mutation
- Replication of muted cells
What are some diseases that are caused by stochastic effects?
- Leukemia
- Thyroid cancer
- Salivary gland tumors
- Heritable disorders
Does deterministic or stochastic effects require a threshold dose?
Deterministic, sufficient cell killing required to produce a clinical response
Why does stochastic effects not require a threshold dose?
Single photon can cause changes in DNA
Is the severity proportional to the dose in deterministic or stochastic effects?
Deterministic effects
What effects are an all or nothing response?
Stochastic effects
In deterministic effects, is the probability of having an effect and the dose related?
No, is independent, all individuals show effect when dose is above threshold
In stochastic effects, is the probability of having an effect and the dose related?
Yes, frequency of effect is proportional to dose, greater the dose the greater of having an effect is
What is radiation induced cancer an effect of?
Stochastic effect
What is mucositis from radiation therapy an effect of?
Deterministic effects
What organs are have a low radio sensitivity?
- Neurons
- Muscles
What organs are have a high radio sensitivity?
- Lymphoid organs
- Bone marrow
- Testes
- Intestine
- Mucous membrane
What is the average dose in dental x-rays for occupationally exposed individuals?
0.2mSV-1% of the allowable dose
Is there a limit on exposure a patient can receive for diagnostic imaging?
No
Justification principle in radiation protection?
Identifying a situation where the benefit to patient from diagnostic exposure likely exceeds the risk of harm
Optimization principle in radiation protection?
Dentist should use every reasonable means to reduce unnecessary radiation exposure to their patients, staff, and themselves
ALARA
As low as reasonably achievable
Dose limitation principle in radiation protection?
Exposure should be limited to occupational and the public, applied to dentist and their staff
Aluminum filter function
Remove low energy photons
How does an aluminum filter affect beam intensity and mean energy?
- Beam energy decreases
- Mean energy increases
Less than 50 kVp requires what type of aluminum filter?
0.5mm
50 to 70 kVp requires what type of aluminum filter?
1.5 mm
Greater than 70 kVp requires what type of aluminum filter?
2.5 mm
What are the two types of collimation?
Round and rectangular
What is collimation?
Metallic barrier with hole in the middle to restrict the size of the beam
What PID is preferred for dental?
Rectangular
What is the maximum recommended beam collimation in diameter?
2.75 inches
What does low kVp generate?
Low energy photons
Do low energy photons contribute to images?
No
Does a long PID/focal length increase or reduce effective dose?
Reduce
Does a long PID/ increased focal length make the image more or less sharp?
More sharp
Should you stand in the primary beam?
No
Where should the provider stand during x-rays?
- 6 ft away
90 to 135 degrees to the primary beam
Should you hold the film in the patient’s mouth for them?
No
