Protection Flashcards
what is ALARA and ALADA?
as low as reasonably achievable / as low as diagnostically acceptable
What are the mandated dose reduction mechanisms for the xray tube head?
collimation & filtration
What does filtration do?
limits amount of low energy radiation
*which contributes to dose, but not dianostic quality
What is the “best” filter & what do we use / why?
- Lead (blocks all rays)
- aluminum bc blocks only low energy / increases mean energy of beam
What is the mandated aluminum filtration for 50-70kv?
1.5mm filtration
Maximum diameter of beam collimation on exit side? Preferred shape?
2.75” diameter // rectangular (not mandated tho)
What are optional dose reduction mechanisms for the xray tube head?
- rectangular collimator
- high kV generator/transformer
- constant potential (DC) fully rectified
- increased focal length
Why does rectangular collimation reduce dose?
less area exposed due to smaller area
What is the tru-align?
rectangular collimator with a magnet to help with beam alignment
– bulkier & snapping moves sensor/pt
What reduces the dose more rectangular vs round collimator or PSP vs CCD?
rectangular !!! 5x less dose
What are the drawback of high kV units?
larger, heavier, more expensive
T/F the higher the kV, the lower teh dose?
true
Benefits of long BID/cone length)?
- 27% less head volume (exposed)
- reduced effective dose
- sharper image
What is a recessed xray tube?
within the tube head, the xray tube is farther back to increase the focal distance (sharper image & lower dose)
Practice options for dose reduction?
- sensor speed (sensitivity)
- Lead thyroid collar
- film-holding devices with beam alignment capability
- time-temperature or digital quality control processing
What type of sensor is the most sensitive to xrays? Lowers dose.
CCD
How should the operator stand during an exposure?
- behind a barrier
- 6 feet from pt & between 90-135* from beam
Annual occupational whole body exposure should not exceed? If pregnant?
50 mSv
5 mSv
What statutes does the NOMAD machine violate?
- distance from patient is NOT 6ft or behind barrier
What is a must for hand held units?
- backscatter shield must be permanently mounted to cone
- operators wear monitor device & evaluated monthly
- must have training
How to maximize operator’s area of protection while using hand-held machine?
- backscatter shield should be at end of PID & held close to pt
- all body parts remain in shield’s protection
- stand directly behind machine & parallel to floor (sensor, shield, operator)
What should you explain to a patient who is fearful of dental radiography?
- magnitude of risks is small
- what we do to minimize risks (radiation protection)
- benefits of radiographic examination
What are the benefits of dental radiography?
- interproximal caries dx
- severity/depth of caries
- PD bone loss & calculus
- root configuration
- periradicular pathosis
- basal bone pathology in jaws
- 3rd molar roots & IAC
- anatomy assessment for implants
What root abnormality is common in asian populations?
diverging lingual root of mandibular 1st molar
Where is hyperdontia most common?
premolar region
What is deterministic risk?
- severity is proportional to dose
- has a threshold
Examples of deterministic risk
- erythema
- xerostomia
- cataract
- osteoradio-necrosis
- fertility
- alopecia
- fetal-development
What are stochastic effects?
- no threshold
- probability of occurrence is proportional to dose
- severity of effects does NOT depend on dose
**any dose there is a risk, but it is low // every time you apply it, probability rises
What is the definition of maximum permissible dose?
the amount of radiation which in the light of present knowledge will not produce any serious, harmful, or deleterious effects on the individual receiving it
What is the maximum permissible dose for operators vs non-operators?
50mSv (5 rem/year) // pregnant: 5mSv
5mSv (.5rem/year)
What is the source of the majority of the average annual effective dose of ionizing radiation?
natural: cosmic, terrestrial, radon (2.0)
total = 3.00
What fraction of radiation exposure comes from medical/dental xrays?
1/6 (.52 –> 3.2)
… BUT in 2007, white paper said it increased to about 1/2
6x increase
How much ionizing radiation do we experience annually?
3.6mSv
**jumped to 6.3mSv if lots of CT/nuclear medicine
To overcome this increased exposure, what must / did we do?
- justify need for xray
- trained and educated
Why are pediatric patients at higher risk/radiosensitivity?
- rate of cellular & organ growth
- greater life expectancy –> greater risk of afflicted with radiation induced cancer
Describe populations likelihoods of developing radiation cancer?
females <10, 5-6x more likely
males <10, 4-5x more likely
females 20-30, 3x more likely
@40 slow drop off from 2.8x more likely
What is the average daily background radiation dose?
8.5 uSv
What types of cancer have the highest risk for dental radiographic exposure?
leukemia & thryoid
Studies show risk for congenital defects are negligible at ___?
50mSv or less
Is fetal development a deterministic or stochastic risk?
deterministic
What is the stochastic risk estimate for pregnancy?
absorbed dose ~25mGy doubles the natural childhood cancer rate from 1in 500 to 1 in 250
Radiation induced cancer threshold dose?
none…always a risk
**risk from dental xrays not seen in doses <10mGy
When to request dental radiographs in pregnant women?
- if clinically indicated, justified
- dose as low as diagnostically possible
- if urgent tx required to benefit baby/mother
–> abscessed tooth/fractured tooth, etc.
When NOT to request dental xrays in pregnant women?
- new patient/recall exams… wait until post-partum
