Radiation Safety

what radiation dose quantity is most used in expressing radiation risk

effective dose

How would increasing the source to skin distance impact scatter and image noise

expose less of the pt, less scatter thus dec noise, beam intensity will dec

how are radiation dose contributions estimated

effective doses from different sources based on population averages

what are the two main contributors to dose from various sources

• background 50%

• medical 50%

what are the four main contributors to background radiation

• radon-22

• cosmic (space)

• internal radionuclides

• terrestrial

of background radiation contributors, which is the main contributor

radon-22

how are you exposed radon-22

naturally everyday: radioactive element naturally occuring on earth’s crust (is also the 2nd most freq cause of lung cancer)

how are you exposed to cosmic radiation

primarily from high altitude/elevation, air travel

how are you exposed to internal radionuclides

foods, like banana

how are you exposed to terrestrial radiation

radioactive nuclides in soil

what is the largest contributor to exposure from human-made sources of radiation

CTs → dx imaging for medical

why have we noticed a dec in effective doses in medical imaging

technology is improving and dose is decreasing

biological manifestations of ionizing radiation damage are primarily a consequence of…

DNA damage

is most DNA damage form x-rays due to indirect or direct actions

indirect actions

how do indirect actions of radiation cause DNA damage

photons or secondary e- react w water to create free radicals → these free radicals have unpaired valence e- are v reactive and will cause lots of DNA damage

how does direct damage of DNA happen from radiation

e- will directly hit the DNA

direct and/or indirect damage of DNA will result in one of three cell responses and will lead to different effects later down the road. explain the cell response and its path it goes down

• enzymatic repair → result in normal funx

• DNA mutation → stochastic effects

• cell death → tissue rxns

radiosensitivity of the cell to cell death is determined by two main factors…

• miotic rate of the cell

• degree of differentiation

what cell would be most sensitive to radiation

a rapidly dividing undifferentiated cell (CHILDREN)

what cell would be the most radioresistant

post-mitotic cells

Casarrett classification has predicted the sensitivity of tissues/organs to tissue rxns form radiation-induced cell killing. the most sensitive tissues/organs exposed during head/neck imaging is…

1. thyroid gland

2. salivary glands

tissue reactions are also known as…

deterministic

does deterministic/tissue rxn have a threshold, explain

yes: rxns will only happen when threshold has been met → consequence is cell death in tissue or organ

does stochastic have a threshold, explain

no: there is no “safe” dose, a single photon x-ray has the potential to cause a DNA mutation but a v small chance

what is the only relevant stochastic effect in humans we are concerned about

carcinogenesis

how is the severity effected comparing to the threshold of deterministic/tissue rxn

severity of effect is proportional to dose one threshold is reached

how is the probability of a stochastic event related to dosage

probability of radiation-induced DNA damage sites inc w dose

dx radiation levels are well below threshold to cause ________________ but do not pose a risk of causing ___________effects

tissue rxn; stochastic

____________ is the only adverse effect of concern from dx imaging

cancer

_____ at exposure strongly influences risk of stochastic effects

age

can you tell the difference between radiation-induced cancers vs spontaneous cancers

no, look the same in every aspect

is the risk of radiation-induced tumor induction approximately threefold higher in children or adults

children

what are the main stochastic effects we are concerned about

• leukemia

• thyroid cancer

• salivary gland tumors

• breast cancer

• brain and nervous system cancer

radiation-induced leukemia shows no detectable risk above the age of…

30

radiation-induced thyroid cancer shows no detectable risk over the age of…

20

are radiation-induced salivary tumors mostly benign or malignant

benign

in radiation-induced breast cancer, there is risk posed before the age of…

20

radiation-induced breast cancer shows no detectable risk after the age of

50

what is the evidence behind radiation-induced heritable effects

no evidence supporting this → no rationale to shield gonads from radiation during dx radiography

are tissue rxns or stochastic effects NOT encountered in dx maxillofacial radiography

tissue rxns

_____________ radiation delivers doses that exceed threshold for tissue rxn

theraputic

what are the two known tissue rxns that were mentioned

• cataracts

• embryo and fetus

what is cataracts

clouding or opacification of the lens

the ICRP estimated a threshold for cataract induction of…

0.5 Gy

the NCRP estimated a threshold for cataract induction

1-2 Gy

why are we not concerned w cataract tissue rxn w dental x-rays

absorbed dose in lens during dental radiograph is well below threshold: 0.2-0.4 Gy

embryos and fetuses are considerably very radiosensitive, but why are we not concerned w pregnant people getting x-rays

they are already getting background radiation, dx poses no risk to pregnant pts or embryo/fetus; tissue rxn threshold is well above expected dosage for fetal imaging

radiation-induced cancer in utero is not observed w doses <____mGy

10

what is the accepted model currently as the approach to develop radiation protection guidlines

the linear no-threshold model (LNT)

what are characteristics of the LNT model

• linear relationship between dose and cancer risk, this continues even at low dose

• no threshold or safe dose below which there is no added cancer risk

• conservative approach

when communicating risk, what are the two factors included

• effective dose

• use of relatable comparison

how is effective dose measured and what is it for

measured using phantom or modeled by computer; used to compare risks from different radiographic exams to convey relative risk of magnitude

what does effective dose not consider / not represent

does not consider age, sex, individual susceptibility factors; does not represent a pts dose

what are the 3 guiding principles in radiation protection

• justification

• optimization

• dose limitation

what is justification when talking about the guiding principles in radiation protection

identify situations where benefit to pt from the dx exposure likely to exceed risk of hazard

what is optimization when thinking about the guiding principles in radiation protection

use every reasonable mean to reduce unnecessary exposure

what acronym can be used when thinking about optimization in the guiding principles in radiation protection

As

Low

Aa

Reasonably

Achievable

what is dose limitation when thinking about the guiding principles in radiation protection

dose limits for occupational and public exposures to ensure no individuals are exposed to unacceptably high doses; no dose limits for individuals exposed to dx purposes

what is pt selection

pt circumstances that suggest high probability imaging would provide info affecting their dx, tx, or prognosis

before conducting any radiographic x-ray, what are the 4 steps clinicians should be taking, but aren’t rlly doing

1. complete a clinical exam and pt assessment

2. consider pts oral and medical history

3. consider pts specific oral disease risk

4. view previous radiographs

the most effective approach to reduce unnecessary exposure is to reduce…

unnecessary radiographs

what is a collimator

metallic barrier w aperture to shape and restrict x-ray beam size and volume of tissue irradiated

what is the difference between a round vs a rectangular collimator

round: built into open-ended aiming cylinders

rectangular: further limit beam size to just larger than the intraoral receptor

what effect does a collimator have on pt exposure

reduces it; rectangular > round

what effect does a collimator have on image quality

improves image quality by reduce scatter (compton)

what is the inverse square law

is the x-ray beam intensity: # of photons per cross-sectional area per unit exposure time

what can the inverse square law be affected by

varies w distance from the focal spot; dec in intensity as beam spreads out (diverges) moving away from source

beam intensity is _________ (inversely/ directly) proportional to the square of the distance from source

inversely

what are some practical applications for the inverse square law

• changes from short to long aiming tube dec beam intensity; requires a corresponding modification of kVp or mA to maintain same intensity at receptor

• inc operator distance from source is an effective method to minimize operator dose

a longer source to skin distance has what affect on beam divergence and exposure

longer → less divergent beam → reduced tissue exposure

what is the minimum source to skin distance to dec exposure

20 cm

what effect dose a long source to skin have on image quality

is associated w “long source to object” distance so this will dec image magnification

what is the purpose of filtration

to preferentially remove low-energy x-ray photons form the beam; results in dec pts exposure w no loss of radiographic information

how are units of filtration expressed

mm of Al

what is the requirement by the US federal regulations require the total beam filtration to be equivalent to…

1.5 mm of Al for a machine operating at 50-70 kVp

what is the usual kilovoltage (kVp) for intraoral radiographs, why

60-70 kVp; provides adequate dx quality w reduced radiation dose

image density is controlled by the __________ (quantity/quality) of x-ray produced, which is best controlled by the combination of ____________ and _____________

quantity is best controlled by mA and exposure time

what is the most crucial factor in influencing dx quality

exposure time

what changes have been made about the recommendation of shielding

pt gonadal and fetal shielding during dx intraoral, pano, cephalometric, and CBCT be discontinued

shielding does not protect against internal scatter radiation; most pt dose compes form internal scatter radiation

what type of collimator can dec thyroid dose from the primary beam

rectangular collimation

when should you NOT use thyroid shielding

for pano or lateral cephalometric

what can thyroid shielding cause to imaging

artifacts that can degrade image quality and require retakes

for radiographs, is verification of pregnancy still required

NO LONGER REQUIRED

what are the 3 principles of personal protection of reduction of radiation

• time

• distance

• shielding

what is the position in distance rule

when barrier or shielding is not available, operator should stand at east 2 meters (6 ft) from tube head and out of the primary beam path at an angle of 90-135 degrees to the central ray