Consider the following dose data from three different CT scans. Which procedure has the highest risk of acquiring radiation-induced cancer?
A. Procedure 1: Absorbed Dose = 21 mGy, Effective Dose = 11 mSv
B. Procedure 2: Absorbed Dose = 80 mGy, Effective Dose = 3 mSv
C. Procedure 3: Absorbed Dose...
Computed Tomography - Radiation Safety || QUESTIONS
& ANSWERS RATED 100% CORRECT!!
Consider the following dose data from three different CT scans. Which procedure has the
highest risk of acquiring radiation-induced cancer?
A. Procedure 1: Absorbed Dose = 21 mGy, Effective Dose = 11 mSv
B. Procedure 2: Absorbed Dose = 80 mGy, Effective Dose = 3 mSv
C. Procedure 3: Absorbed Dose = 34 mGy, Effective Dose = 10 mSv
D. All risks are equal correct answers A. Procedure 1: Absorbed Dose = 21 mGy, Effective
Dose = 11 mSv
Procedure 1 has the highest risk of acquiring radiation-induced cancer. The risk of developing
a radiation-induced cancer is based almost exclusively on the effective dose, therefore, the
procedure with the highest effective dose will usually have the highest risk of developing
cancer.
Radiation exposure is calculated with units of:
A. Joules/kilogram (J/kg)
B. Coulombs/kilogram (C/kg)
C. Milligray (mGy)
D. Millisievert (mSv) correct answers B. Coulombs/kilogram (C/kg)
Exposure measures the amount of ionization created in air from x-rays. In the SI system of
units and measures, exposure is represented with units of Coulombs/kilogram (C/kg). The
more familiar unit used in the traditional system for exposure is the Roentgen.
Concerning radiation-induced cancer, increasing the radiation dose to a patient results in:
A. Increased severity of cancer
B. Decreased severity of cancer
C. Increase probability of cancer
D. Decreases probability of cancer correct answers C. Increase probability of cancer
Increasing radiation dose increases the probability of cancer, but it does not increase the
severity of cancer. A cancer caused by 3 Gray (Gy) of radiation is no worse than a cancer
caused by 2 Gy of radiation. Radiation dose only affects the total probability.
Which two of the following interactions may result in an x-ray photon being emitted out of
the patient in a different direction than the original path? (Select two)
A. Coherent scattering
B. Photoelectric absorption
C. Compton scattering correct answers A. Coherent scattering, & C. Compton scattering
When a photon changes direction as a result of an interaction in an atom, this is called
scattering. Both coherent scattering and Compton scattering cause the photon to change
direction when it is emitted out of the patient. Photoelectric absorption results in total
absorption of the photon, so no photon is left over to be scattered.
The energy of ions created in air from x-ray is called:
A. Exposure
B. Air Kerma
C. Absorbed Dose
,D. Equivalent Dose
E. Effective Dose correct answers B. Air Kerma
Air kerma is a measurement defining the energy of ions created in air from radiation, such as
x-rays. This is slightly different from exposure, which measures the total amount of
ionization in air.
Which of the following materials will result in the highest x-ray transmission reading?
A. Air
B. Cortical Bone
C. Muscle
D. Iodine correct answers A. Air
A high transmission reading is the result of a high number of photons passing through the
material without being attenuated. Air does not attenuate much radiation, which would result
in a very high transmission reading.
Which two of the following radiation effects only occur at a specific dose threshold? (Select
two)
A. Cataracts
B. Bronchogenic carcinoma
C. Leukemia
D. Skin Erythema correct answers A. Cataracts, & D. Skin Erythema
A radiation effect with a threshold is also called a deterministic effect. Cataracts and skin
erythema are both deterministic effects because they only occur once a specific radiation dose
threshold has been reached. Below this threshold, they do not occur. Leukemia and
bronchogenic carcinoma are forms of cancer and may be caused by any dose of radiation.
Air kerma is measured in units of:
A. Coulombs/kilogram (C/kg)
B. Milligray (my)
C. Millisievert (mSv)
D. Becquerel (Bq) correct answers B. Milligray (my)
KERMA is an acronym which stands for kinetic energy released per unit mass. It is measured
in units of Gray (Gy) or milligray (mGy).
What term describes radiation-induced hair loss?
A. Oligospermia
B. Urticaria
C. Erythema
D. Epilation correct answers D. Epilation
The medical term for hair loss is epilation or alopecia.
Which effect is most likely to occur in a patient who receives a very small dose of radiation?
A. Cataracts
B. Epilation
C. Skin burns
D. Cancer correct answers D. Cancer
, Cancer is a stochastic effect, and one that may occur after receiving a very small dose of
radiation. In other words, any dose of radiation potentially increases the risk of cancer. Other
effects, like cataracts, epilation, and skin burns all require much higher doses of radiation
before they occur.
Consider this scenario: During a CT scan of the chest, the technologist administers a radiation
dose of approximately 3,000 milligray (mGy). Which two of the following effects may
occur? (Select two)
A. Cataracts
B. Epilation
C. Cancer
D. Decreased fertility correct answers B. Epilation, & C. Cancer
Epilation and cancer are both possible effects following a 3,000 mGy radiation exposure to
the chest. Epilation (hair loss) is a deterministic effect that can occur at this radiation dose.
Cancer is a stochastic effect that potentially occurs at any dose of radiation. Cataracts and
decreased fertility are deterministic effects that can occur at this dose level, but ONLY when
the eyes and gonads are directly exposed.
For deterministic effects of radiation, increasing dose result:
A. Increased severity of the effect
B. Decreased severity of the effect
C. Increase probability of the effect
D. Decreases probability of the effect correct answers A. Increased severity of the effect
For deterministic effects, increasing the dose increases the severity of the effect once the
threshold has been crossed. For example, skin erythema caused by 3 Gray (Gy) of radiation is
worse than that caused by 2 Gy.
Increasing the kilovoltage peak (kVp) for a CT procedure results in:
A. Increased attenuation
B. Decreased attenuation
C. No change in attenuation correct answers B. Decreased attenuation
On average, increasing kVp decreases the total percentage of photons attenuating in the
patient. But don't be confused on how this affects patient dose. kVp also has a substantial
effect on the beam intensity (quantity). Although a lower percentage of photons are
attenuated, a higher total number of photons get absorbed in the patient because there are so
many more photons in the beam.
Effective dose is measured with units of:
A. Coulombs/kilogram (C/kg)
B. Milligray (mGy)
C. Miillisievert (msv)
D. Becquerel (Bq) correct answers C. Miillisievert (msv)
Both equivalent dose and effective dose are measured in units of Sievert (Sv) or millisievert
(mSv).
Equivalent dose is described with units of:
A. Coulombs/kilogram (C/kg)
B. Milligray (mGy)
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