4.0 Interactions of X-ray with Matter Flashcards
______________
- Depending on which part of the globe you live in, There is considerable variation in background radiation exposure — the global average is ________, and the typical global range is 1 to 13 mSv.
- Without us knowing, we are constantly bathed in natural background radiation. We receive this constant background radiation from space and terrestrial sources.
Background Radiation
2.4 mSv/year
1 to 13 mSv.
— _________
— Radioactive element from decay of uranium-238
— Gas
— Polonium-218 emit α particles
— ____% of the background exposure in the world
— Cause for 10,000 to 20,000 of lung cancer deaths per year (in the U.S. mostly smokers)
Radon-222
73
_____________
— Comes from the sun or cosmic rays
— Composed of protons, helium nuclei, and nuclei of heavier elements
— ___% of background radiation
Space Radiation
11
_____________
— Comes from foods containing uranium and thorium and their decay products
— __% of background exposure.
Internal Radionuclides
9
____________
— Radioactive nuclides in the soil
— primarily potassium-40 and the radioactive decay products of uranium-238 and thorium-232
— __% of background exposure
Terrestrial Radiation
7
_______________
— 3.6 billion x-ray and nuclear medicine examinations performed yearly worldwide
— ___% dental radiographic examinations.
— Computed Tomography of the chest and abdomen, and cardiac nuclear medicine studies.
— CT scans contribute more than half of medical radiation exposure.
—____% dental imaging of the total exposure from medical imaging.
Medical Exposure
14
0.26
» The average person in the United States receives approximately as much radiation from medical and consumer products sources (_______) as from natural background exposure.
» Most medical x-ray exposures come from computed tomography (CT), nuclear medicine (primarily cardiac imaging), fluoroscopy, and conventional radiography.
» Exposures from dental examinations and from occupational, fallout, and nuclear power sources are _______.
» Although individuals with exposures from natural background are fairly evenly distributed in the population, most medically exposed individuals are relatively _________
3.1 mSv/year
small
old and sick.
________________
— Cigarette smoking, building materials, air travel, mining and agriculture, and combustion of fossil fuels.
— Air travel produce cosmic radiation.
— Minor sources of consumer product exposure: dental porcelains, television receivers, and smoke alarms.
— ____% total average exposure
Consumer Products
1.6
_____________
— Caregivers or people who are in contact with patients receiving nuclear medicine treatments; people working in nuclear plants; individuals involved in areas of industrial, medical, educational, or research activities; workers in medical and dental x-ray facilities; workers in airport baggage inspection systems; and commercial flight personnel.
— _____ average annual exposure
Other Sources
0.1%
When needed, the basic principle of diagnostic imaging is that the _________________ far outweighs the radiation-associated risks.
To satisfy this principle, _______ from dentomaxillofacial radiographic examination must be:
Optimized to produce a diagnostically acceptable image, and
Less than the threshold needed to cause any deterministic effects, and
Minimized to keep the risk of stochastic effects within an acceptable range.
benefit to the patient
doses
Estimating Cancer Risk from Diagnostic Dentomaxillofacial Radiology
_____________
o There is no threshold or “safe dose”.
- ________ – low-dose radiation may have a protective effect.
- Linear No-Threshold (LNT)
Hormesis
» Doses of radiation higher than approximately 100 mSv (greendots) result in a dose-dependent increase in the cancer rate.
» The ________________ posits that at doses less than 100 mSv, there is a linear relationship between dose and risk (orange dashed line) and that there is no threshold dose below which there is no additional risk.
» Alternate models propose that risk may be higher or lower than those predicted by the LNT model and that low doses may have a____________ with a threshold dose.
» The LNT model is currently accepted as the approach to develop radiation protection guidelines.
linear no-threshold model (LNT)
protective effect
Communicating Radiation Risks to Patients
* Allow the patient to fully express his or her thoughts. Do not interrupt the patient’s comments or belittle the patient’s concerns. Acknowledge their concerns and indicate that you understand their apprehension.
- Tell the patient why you need radiographs as part of the patient’s personal diagnosis-such as the detectior of interproximal caries, the extent of bone loss from periodontal disease suggested by probing, periapical infections suggested by pain, or any anticipated findings specific to the patient’s condition that are important and can be attained only by radiologic investigation. Assure new patients that you will contact their previous dentist to obtain previous radiographs that may assist you in their diagnosis.
- Reassure the patient that you make efforts to minimize their radiation dose. Describe the many measures you take to reduce patient exposure, such as using fast film or digital sensors, rectangular collimation, and thyroid collars. With these assurances, including that you will make only the exposures you specifically need for the patient’s benefit, most patients will appreciate your attention to their concerns and accept radiographs.
- Convey the relative magnitude of the dose that the patient is likely to receive. Table 3.2 provides information on typical effective doses from dentomaxillofacial radiography. However, these doses are not easily comprehended by patients rather, convey the relative magnitude of the dose in terms of equivalent days, months, or years of natural background radiation (see Fig. 3.3). To help the patient place the risk in perspective, compare the magnitude of these risks with other sources of radiation exposure such as an airline flight or other common imaging procedures. Note that dentomaxillofacial radiography delivers negligible to minimal doses, relative to other medical imaging procedures.
- Often patients who are pregnant may require radiographic examination. Dental practices should implement a policy to identify pregnancy in patients who are of childbearing age. This can be accomplished by reviewing the patient’s menstrual history and by direct inquiry of whether the patient thinks that she may be pregnant. Routine radiographic evaluation of asymptomatic pregnant patients may be deferred until after pregnancy. When radiographs are needed for management of a pregnant patient, emphasize that the diagnostic and treatment planning benefits are crucial to maintain oral health, and that dental disease and its sequelae could have an adverse impact of the health of the unborn child. If the patient is concerned about the potential adverse effects of diagnostic radiation on the fetus, emphasize that the fetal doses from dentomaxillofacial radiography are approximately 42,000-fold lower than the threshold dose for deterministic effects on the embryo and fetus.
- The dentist should identify situations where the benefit to a patient from the diagnostic exposure likely exceeds the risk of harm.
- No practice shall be adopted unless its introduction produces a positive net benefit.
- Justification
- Dentists should use every reasonable means to reduce unnecessary exposure to their patients, their staff, and themselves.
- This philosophy of radiation protection is often referred to as the principle of __________
- ALARA holds that exposures to ionizing radiation should be kept as low as reasonably achievable, with economic and social factors being taken into account.
- Optimization
ALARA (As Low As Reasonably Achievable).
______________
* Provides dose limits for occupational and public exposures to ensure that no individuals are exposed to unacceptably high doses.
* The dose equivalent to individuals shall not exceed the limits recommended by the ICRP (limitation). This principle applies to dentists and their staff who are exposed occupationally but not to patients because there are no dose limits for individuals exposed for diagnostic purposes.
- Dose Limitation
_____________
* Radiographic screening for the purpose of detecting disease before clinical examination should not be performed.
* A thorough clinical examination, consideration of the patient history, review of any prior radiographs, caries risk assessment and consideration of both the dental and the general health needs of the patient should precede radiographic examination (ADA 2012).
Patient Selection Criteria
________________
* When the dentist has determined that a radiographic examination is justified (using patient selection criteria), the specific radiographic protocol or the principle of optimization greatly influences patient exposure to radiation.
* Considerations for designing an optimal radiographic study include choice of equipment, choice of exposure settings, operation of equipment, and processing and interpreting the radiographic image.
Conducting the Examination
- Good radiologic practice includes use of the _____ image receptor compatible with the diagnostic task (F-speed film or digital) (ADA 2012).
Intraoral dental x-ray film is available in two speed groups: D and E/F. Clinically, film of speed group _____is approximately twice as fast (sensitive) as film of group D and thus requires only half the exposure. Fast films are effective for ________. Multiple studies have found that E/F-speed film provides the same useful density range, latitude, contrast, and image quality as D-speed films without sacrifice of diagnostic information. Current digital sensors offer equal or greater dose savings than does E/F-speed film, and comparable diagnostic utility.
fastest
E/F
exposure reduction.
Intensifying Screens and Films
*__________are recommended… combined with high-speed film of 400 or greater (ADA 2006).
* _________ (2)
Rare-earth intensifying screens
Gadolinium and lanthanum
Source-to-Skin Distance
* Use of long source-to-skin distances of 40 cm, rather than short distances of 20 cm, decreases exposure by 10 to 25 percent.
* Distances between _____________ are appropriate, but the longer distances are optimal (ADA 2006).
Two standard focal source-to-skin distances have evolved over the years for use in intraoral radiography—20 cm (8 inches) and 40 cm (16 inches).
With a longer source-to-skin distance, the x-ray beam is less _______ reducing the exposed tissue volume (Fig. 3.5).
The use of a longer source-to-object distance also decreases image ___________ (see Fig. 7.3).
20 cm and 40 cm
divergent,
magnification
Rectangular Collimation
* Since a rectangular collimator decreases the _______ by up to fivefold as compared with a circular one, radiographic equipment should provide rectangular collimation for exposure of periapical and bitewing radiographs (ADA 2012).
FIG 5-4. Collimation of an x-ray beam (blue) is achieved by restricting its __________
» A, Circular collimator.
» B, Rectangular collimator restricts area of exposure to just larger than the detector size and thereby reduces unnecessary patient expo- sure.
Radiation dose
useful size.
Consequently, further limiting the size of the x-ray beam to the size of the image receptor significantly reduces unnecessary _____________
If the tissue volume exposed is decreased, the amount of scattered radiation is decreased, image fogging is decreased, and the resultant image has improved ____________
_____________ reduces the area of the patient’s skin surface exposed by 60% over that of a round collimated (7-cm diameter) beam.
patient exposure.
diagnostic quality.
Rectangular collimation
- The purpose of ________ is to preferentially remove these low-energy xray photons from the x-ray beam
- 1.5 mm of aluminum for a machine operating at 50 to 70 kVp and 2.5 mm of aluminum for machines operating at higher voltages.
_______ results in decreased patient exposure with no loss of radiographic information.
filtration
filtration
Protective Aprons and Thyroid Collars
* The ________ is more susceptible to radiation exposure during dental radiographic exams given its anatomic position, particularly in children.
* Protective thyroid collars and collimation substantially reduce radiation exposure to the thyroid during dental radiographic procedures.
* Because every precaution should be taken to minimize radiation exposure, protective thyroid collars should be used whenever possible (ADA 2012).
thyroid gland
Film and Sensor Holders
* __________ that align the film precisely with the collimated beam are recommended for periapical and bitewing radiographs (ADA 2006).
Film or digital receptor holders should be used when intraoral radiographs are made because they improve the alignment of the film, or digital sensor, with teeth and the x-ray machine. Their use results in a significant reduction in unacceptable images and thus avoidable retakes.
The use of ______________ allows the operator to control the position and alignment of the film or sensor with respect to the teeth and jaws.
Film holders
film and sensor holders
- The optimal operating potential of dental x-ray units is between _____________ (ADA 2012)
60 and 70 kVp
Milliampere-Seconds
* The operator should set the amperage and time settings for exposure of dental radiographs of optimal quality (ADA 2006).
* ___________is controlled by the quantity of x-rays produced, which is best controlled by the combination of milliamperage and exposure time, termed milliampere-seconds.
* Should be set at the ___________ setting.
Image density
highest mA
- All film should be processed following the film and processer manufacturer recommendations. Poor processing technique, including sight-developing, most often results in underdeveloped films, forcing the x-ray operator to increase the _____ to compensate, resulting in patient and personnel being exposed to unnecessary radiation (ADA 2012).
dose
- The dentist should view radiographs under appropriate conditions for analysis and diagnosis (ADA 2006).
- Semi-darkened room with light transmitted through the films;
- All extraneous light should be eliminated.
- In addition, radiographs should be studied with the aid of a __________________ to detect even the smallest change in image density.
magnifying glass
Operators of radiographic equipment should use _______ protection when possible, and barriers should contain a leaded glass window to enable the operator to view the patient during exposure.
When shielding is not possible, the operator should stand at least ____________ from the tube head and out of the path of the primary beam (ADA 2006).
- Lead walls or mobile lead barriers.
- Exposure switch should be located behind these barriers.
- Barrier should have a leaded window to allow visual and verbal contact with the patient during exposure.
- Walls of clinic near x-ray machine should be shielded from nonoccupational individuals.
barrier
two meters
