How can we help?

You can also find more resources in our Help Center.

61 terms

Radiation exposure & monitoring

STUDY
PLAY
The tabletop exposure rate during fluoroscopy shall not exceed
10 R/min
Filters are an important component of film badges. Their function is to
identify the quality of radiation exposure.
familiar radiation monitor is the film badge
consists of special radiation dosimetry film packaged like dental film and is enclosed in a special plastic holder. The plastic holder features an open window (through which the user's name appears) and various filters, which serve to identify the type and energy of radiation. For example, radiation that exposes film behind an aluminum filter is more energetic than radiation that only passes through the open window, and less energetic than radiation penetrating a copper filter. The degree of exposure is carefully evaluated and equated to a dose, usually expressed in mrem; the film badge can measure doses as low as 10 mrem.
The purpose of filters in a film badge is
to measure radiation quality; the filters (usually aluminum and copper) serve to help measure radiation quality (energy). Only the most energetic radiation will penetrate the copper; radiation of lower levels of energy will penetrate the aluminum, and the lowest energy radiation will pass readily through the unfiltered area. Thus, radiation of different energy levels can be recorded, measured, and reported
What unit of measurement expresses the amount of energy deposited in tissue?
Rad (Gy); is equal to 100 ergs of energy per gram of any absorber
the following are acceptable ways to monitor the radiation exposure of those who are occupationally employed
1. TLD
2. OSL
To within what percentage of the SID must the collimator light and actual irradiated area be accurate?
2%
Medical and dental radiation accounts for what percentage of the general public's exposure to man-made radiation?
90%
The person responsible for ascertaining that all radiation guidelines are adhered to and that personnel understand and employ radiation safety measures is the
radiation safety officer
The term effective dose refers to
whole-body dose
Every radiographic examination involves an ESE
which can be determined fairly easily. It also involves a gonadal dose and marrow dose, which if needed, can be calculated by the radiation physicist. If the ESE of a particular examination was calculated to determine the equivalent whole-body dose, this is termed the effective dose. For example, the ESE of a PA chest is approximately 70 mrem, while the effective dose is 10 mrem. The effective (whole-body) dose is much less because much of the body is not included in the primary beam.
In which type of monitoring device do photons release electrons by their interaction with air?
Pocket dosimeter
film badge
the film's silver halide emulsion is ionized by x-ray photons
pocket dosimeter
contains an ionization chamber (containing air), and the number of ions formed (of either sign) is equated to exposure dose
Thermoluminescent dosimeter (TLD)
personnel radiation monitors that use lithium fluoride crystals. Once exposed to ionizing radiation and then heated, these crystals give off light proportional to the amount of radiation received
Optically stimulated luminescence (OSL) dosimeter
personnel radiation monitors that use aluminum oxide crystals. These crystals, once exposed to ionizing radiation and then subjected to a laser, give off luminescence proportional to the amount of radiation received
Which unit of exposure is described as 100 ergs of energy per gram of irradiated absorber?
rad; Rad is an acronym for radiation absorbed dose; it measures the energy deposited in any material
The operation of personal radiation monitoring can be based on stimulated luminescence. Which of the following personal radiation monitors function in that manner?
1. OSL
2. TLD
The NCRP recommends an annual effective occupational dose equivalent limit of
5 rem (50 mSv)
Acording to the NCRP, the annual occupational dose equivalent limit to the lens of the eye is
150 mSv
According to the NCRP
the annual occupational whole-body dose equivalent limit is 50 mSv (5 rem or 5000 mrem). The annual occupational whole-body dose equivalent limit for students under the age of 18 years is 1 mSv (100 mrem or 0.1 rem). The annual occupational dose equivalent limit for the lens of the eye, a particularly radiosensitive organ, is 150 mSv (15 rem or 15,000 mrem). The annual occupational dose equivalent limit for the skin and extremities is 500 mSv (50 rem or 50,000 mrem). The total gestational dose equivalent limit for embryo/fetus of a pregnant radiographer is 5 mSv (0.5 rem or 500 mrem)
TLD
a sensitive and accurate device used in radiation dosimetry. It may be used as a personal dosimeter or to measure patient dose during radiographic examinations and therapeutic procedures. The TLD utilizes a thermoluminescent phosphor, usually lithium fluoride. When used as a personal monitor, the TLD is worn for 1 month. During this time, it stores information regarding the radiation to which it has been exposed. It is then returned to the commercial supplier. In the laboratory, the phosphors are heated. They respond by emitting a particular quantity of light (not heat) that is in proportion to the quantity of radiation delivered to it. After they are cleared of stored information, they are returned for reuse
curie
unit of radioactivity, describing disintegrations per second
roentgen
unit of exposure; it measures the quantity of ionization in air
Rad
an acronym for radiation absorbed dose; it measures the energy deposited in any material
Rem
acronym for radiation equivalent man; it includes the relative biologic effectiveness (RBE) specific to the tissue irradiated, and therefore is a valid unit of measure for the dose to biologic material
Types of secondary radiation barriers include
1. the control booth.
2. lead aprons.
3. the x-ray tube housing
How will x-ray photon intensity be affected if the SID is doubled
Its intensity decreases four times
Source-to-image-receptor distance (SID) has a significant impact on x-ray beam intensity (other terms we could use are exposure rate and dose)
As the distance between the x-ray tube and image receptor increases, exposure rate/intensity/dose (and therefore radiographic density) decreases according to the inverse square law. According to the inverse square law, the exposure rate is inversely proportional to the square of the distance; that is, if the SID is doubled, the resulting beam intensity will be one fourth the original intensity; if the SID is cut in half, the resulting beam intensity will be four times the original intensity
The unit of measurement used to express occupational exposure is the
rem (Sv)
Primary barriers
protect from the useful, or primary, x-ray beam and consist of a certain thickness of lead. They are located anywhere that the primary beam can possibly be directed, for example, the walls of the x-ray room. The walls of the x-ray room usually require a 1/16-inch (1.5-mm) thickness of lead and should be 7 feet high
Secondary barriers
protect from secondary (scattered and leakage) radiation. Secondary barriers are control booths, lead aprons, and gloves, and the wall of the x-ray room above 7 feet. Secondary barriers require much less lead than primary barriers
The annual dose limit for occupationally exposed individuals is valid for
beta, x-, and gamma radiations, but not alpha because they ionize in air so quickly
Which of the following personnel monitoring devices used in diagnostic radiography is considered to be the most sensitive and accurate?
OSL; The relatively new OSLs contain aluminum oxide crystals that also undergo characteristic changes upon irradiation. When the Al2O3 crystals are stimulated by a laser, they emit (optically stimulated) luminescence/light in proportion to the amount of radiation absorbed. OSLs can measure exposures as low as 1 mrem
Which of the following affect(s) both the quantity and quality of the primary beam?
1. Half-value layer (HVL)
2. kVp
Kilovoltage (kVp) and half-value layer (HVL) change
both the quantity and quality of the primary beam. The principal qualitative factor of the primary beam is kVp, but an increase in kVp will also effect an increase in the number of photons produced at the target. HVL is defined as the amount of material necessary to decrease the intensity of the beam to one half of its original value, thereby effecting a change in both beam quality and quantity. The mAs value is adjusted to regulate the number of x-ray photons produced at the target. X-ray beam quality is unaffected by changes in mAs.
A dose of 25 rad to the fetus during the fourth or fifth week of pregnancy is more likely to cause which of the following:
skeletal anomalies
most general diagnostic examinations are likely to deliver fetal doses of less than
1 to 2 rad
The largest dose to the male gonads is most likely to result from which of the following exposures?
Cross-table lateral hip
What is the annual dose-equivalent limit for the skin and hands of an occupationally exposed individual?
50rem (500 mSv)
The dose-equivalent limit for the lens of the eye is
15 rem (150 mSv)
An occupationally exposed individual may receive up to
3 rem (30 mSv) in a given calendar quarter, or 13-week period. However, that individual may not exceed 5 rem (50 mSv) in that particular year.
The presence of ionizing radiation may be detected in which of the following ways?
1. Ionizing effect on air
2. Photographic effect on film emulsion
3. Fluorescent effect on certain crystals
According to the NCRP, the annual occupational whole-body dose equivalent limit for students under age 18 is
1 mSv (100 mrem or 0.1 rem).
The total gestational dose equivalent limit for embryo/fetus of a pregnant radiographer is
5 mSv (500 mrem or 0.5 rem).
What is the established fetal dose limit guideline for pregnant radiographers during the entire gestation period?
0.5 rem (500 mrem or 5 mSv)
A thermoluminescent dosimetry system would use which of the following crystals?
Lithium fluoride
OSLs use
aluminum oxide as their sensitive crystal.
The annual dose limit for medical imaging personnel includes radiation from
occupational exposure only
Sensitometry and densitometry are used in evaluation of
the film processor; they are just one portion of a complete quality assurance (QA) program.
Modulation transfer function (MTF)
used to express spatial resolution—another component of the QA program.
A complete QA program includes testing of all components of the imaging system:
processors, focal spot, x-ray timers, filters, intensifying screens, beam alignment, and so on.
The x-ray tube housing must reduce leakage radiation to less than
100 mR/hour at a distance of 1 m from the housing.
he tabletop exposure rate during fluoroscopy shall not exceed
10 R/min
The operation of personnel radiation monitoring devices depends on which of the following?
1. Ionization
2. Luminescence
3. Thermoluminescence
Ionization is the fundamental principle of operation of both
the film badge and the pocket dosimeter.
Radiation output from a diagnostic x-ray tube is measured in which of the following units of measurement?
roentgen
an ion chamber dosimeter instrument is used for
measuring x-ray tube output
the disadvantage of the pocket dosimeter is
that it does not provide a permanent legal record of exposure.
Which of the following is a measurement of dose to biologic tissue?
Rem (Sv)
Rem
an acronym for radiation equivalent man; it includes the RBE specific to the tissue irradiated, and therefore is a valid unit of measurement for the dose to biologic material.