Radiology Textbook Chapter 2/3 + Test 2 Slides

The initial interactions between the incident photon and tissue atoms occur almost instantaneously, within 10−13 seconds after radiation exposure, and subsequent DNA damage is completed within 1 millisecond

In ionization, how fast does the interaction between the incident photon and tissue atoms occur, and separately, the DNA damage?

High-velocity charged particles (alpha particles, beta particles, electrons, and protons) have a high linear energy transfer (LET) and transfer most of their energy over a short distance

What is the LET for alpha particles, beta particles, electrons, and protons?

X-rays and gamma rays are low-LET radiations. They deposit less energy per unit track length and thus penetrate deeper into tissues.

What is the LET for x-rays and gamma rays?

They deposit less energy per unit track length and thus penetrate deeper into tissues.

What does low-LET mean for penetration?

Transfer most of their energy over a short distance. These particles have densely ionizing tracks and penetrate short distances into tissues

What does high-LET mean for penetration?

In direct actions, the photon directly interacts with and ionizes DNA.

What is direct ionizing radiation damage?

In contrast, in indirect actions, photons and secondary electrons ionize water and yield unstable free radicals and oxidizing species that subsequently diffuse and damage DNA.

What is indirect ionizing radiation damage?

Direct actions predominate over indirect actions with high LET radiations but are less frequent with low-LET radiations such as x- and gamma-rays.

In high LET radiations, are direct or indirect radiation damage more common?

Ionizing radiation initiates a complex series of chemical changes in water, collectively referred to as radiolysis of water which leads to free radicals that interact with and produce changes in biologica molecules

Why does indirect radiation damage occur?

Both direct and indirect effects are completed within 10^-5 seconds. The resulting damage may take hours to decades to become evident.

Which happens first in our body: direct or indirect effects, and when do we see the damage become evident?

1/3

What amount of biological effects of x-ray exposure result from direct effects?

1. Peroxyl radicals

2. Hydrogen peroxide

What are the major tissue toxins produced in indirect effects?

2/3

*remember it as we have a LOT of water so it is very easy to make indirect damage

What amount of biological effects of x-ray exposure result from indirect effects?

Damage to a cell's DNA

What is the primary cause of radiation-induced cell death, carcinogenesis, and heritable mutations?

Double-strand breaks because it is harder to repair than a single strang break

What is considered the worst kind of DNA damage and why?

- high LET radiations are more effective at cell killing than low LET radiations.

- Low LET damage is distributed sparsely

- High LET radiations have densely ionizing tracks and cause more double-strand breaks and clustered lesions.

What causes more damage: high or low LET radiation?

When two or more base damages or strand breaks occur within two turns of a DNA helix

What is a clustered lesion in DNA damage?

More difficulte to repair

Because of how close they are together, are clustered lesions easier or harder to reapir?

As Low As Reasonable Achievable

What does ALARA stand for?

Deterministic and Stochastic

What are the two fundamental categories of radiation-induced biologic effects?

Deterministic

What type of effect is caused by cell killing?

Deterministic

What type of biological effect occurs only when the threshold dose is exceeded (Has a threshold)?

Deterministic

What type of biological effect has its effect proportional to the dose?

No. We dont cross the threshold

Are there deterministic effects in dental radiology?

deterministic

Xerostomia, Osteroradionecrosis, Cataracts, and Skin burns are examples of what type of radiation effect?

Stochastic effects

What type of radiation effect is caused by sublethal DNA damage?

Stochastic effects

What type of radiation effect is caused by any dose of radiation that does not have a threshold?

Stochastic

What type of radiation effect has the severity of clinical effects independent of dose?

Stochastic

What type of radiation effect has a all-or-none response to radiation?

Stochastic

What type of radiation effect is proportional to dose such as the higher the dose, the higher the risk of manifesting the effect?

Yes

Do we have stochastic effects in dental radiology?

stochastic effects

Leukemia, thyroid cancer, heritable effects, and radiation-induced skin cancer are examples of what type of radiation effect?

stochastic effects

What type of radiation effect can be caused by a single X-ray photon meaning even the smallest radiation dose can cause heritable effect?

- Leukemia (highest risk in children)

- Thyroid cancer (highest risk in children)

- Salivary gland tumors

- Breast Cancer

- Brain and Nervous System Cancers

What are the risks from diagnostic maxillofacial radiography?

No

Are there radiation-induced heritable effects to humans?

- Stem cells are radiosensitive, mature cells

- Young tissue is more radiosensitive than older tissue

- High metabolic activity is radiosensitive, low metabolic rate is radio-resistant

- Increases in proliferation and growth rates of cells makes them more radiosensitive

- Different cells from various organs of the same individual may respond quite differently

What is the Law of Bergonie and Tribondeau?

- Have a high mitotic rate

- Undergo many future mitoses

- Most primitive in differentiation

What are the characteristics of the most radiosensitive cells?

False. Different cells from various organs of the same individual may respond quite differently

T/F. Different cells from various organs of the same individual may respond the same way to radiation.

True

T/F. Stem cells are radiosensitive, mature cells

True

T/F. Increases in proliferation and growth rates of cells makes them more radiosensitive

False. High metabolic activity is radiosensitive, low metabolic rate is radio-resistant

True/False. Low metabolic activity is radiosensitive, high metabolic rate is radio-resistant

False

T/F. Diagnostic dental imaging can potentially cause tissue reactions in the fetus when imaging a pregnant patient.

No. If the patient does not require immediate treatment, we try to hold off until the patient delivers the baby.

At SIU SDM, if the patient is pregnant, do we do X-rays on them?

The radiation treatment is administered as many daily small doses (fractions). Such fractionation of the total x-ray dose provides greater tumor destruction than is possible with a large single dose. Fractionation also allows increased cellular repair of surrounding normal tissues that are unavoidably exposed. Fractionation also increases the mean oxygen tension in an irradiated tumor, rendering the tumor cells more radiosensitive.

What is radiation treatment?

Deterministic

Cataracts are a ________ effect.

No. The absorbed dose in the lens during dental imagging ranges from 0.02 to 0.4 mGy at least 1250 times lower than the ICRP estimate

Do our patients have to worry about developing cataracts?

1/4

What percentage of healthcare radiographic imaging is dental radiographs?

1. Radon

2. Space

3. Internal

4. Terrestrial

5. Consumer Products

3.1 mSv

What are the natural background categories that give rise to background radiation exposure? What is the combined annual effective dose of ionizing radiation?

1. CT

2. Nuclear Medicine

3. Interventional fluoroscopy

4. Conventional radiography and fluroscopy

5. Dental

What are the medical categories that give rise to background radiation exposure?

True

T/F. All life on Earth has evolved in a continuous exposure to natural background radiation.

Radon

What is the greatest source of background exposure?

1. decay of uranium-238

2. radioactive element in the Earth's crust

3. It is a gas that is released from the ground and enters homes and buildings

4. It emits alpha particles

5. The gas causes 10-20 thousand lung cancer deaths per year, mostly in smokers

6. Found in earth-based materials (concrete, bricks, gypsum wallboard)

7. 52-74% of background radiation

*Test 2 Test Question

What are some characteristics of Radon?

- It is altitude-based, the higher elevation the higher the space radiation exposure

- air travel exposes passengers and crew to cosmic radiation

- aurora borealis is one source

- 11-16%

What are some characteristics of space radiation?

- radionuclides that are ingested

- greatest internal exposure comes from foods containing uranium and thorium

- 9-12%

What are some characteristics of internal radionucleotides?

- Terrestrial radiation exposure is derived from radioactive nuclides in the soil

- 7%-20% of background exposure

What are some characteristics of terrestrial radiation?

- cigarette smoking, building materials, air travel, mining and agriculture, and combustion of fossil fuels.

- 2%-6% of the total average annual exposure

What are some of the consumer product characteristics?

Diagnostic imaging

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

0.26%

How much of the medical imaging exposure comes from dental?

False. There is no threshold or "safe dose" below which there is no added cancer risk. (Cancers can arise from one cell mutation)

T/F. There is a threshold or safe dose below which there is no added cancer risk.

The bystander effect in radiology is when cells not directly hit by radiation, but close to irradiated cells, show DNA damage, mutations, or other harmful biological changes which can impact cancer risk and treatment, suggesting protective agents might block these signals

What is the bystander effect?

Predicts that there is a linear relationship between dose and the risk of inducing a new cancer, even at very low doses (Fig. 3.3). This hypothesis considers that there is no threshold or "safe dose" below which there is no added cancer risk.

What is the linear no-threshold (LNT) hypothesis?

5 days

What is the equivalent background exposure for a rectangular FMS on F speed film?

2.5 days

What is the equivalent background exposure for a rectangular FMS on a CCD sensor?

24 days

What is the equivalent background exposure for a round FMS on F speed film?

12 days

What is the equivalent background exposure for a round FMS on a CCD sensor?

2.5 days

What is the equivalent background exposure for a pano?

15 days

What is the equivalent background exposure for a large FOV?

2 months

What is the equivalent background exposure for a Multidectector CT Maxillofacial (hospital)?

1. Justification

2. Optimization

3. Dose limitation

What are the 3 guiding principles in radiation production?

Justification

What guiding principle: benefit to a patient from the diagnostic exposure likely exceeds the risk of harm?

optimization

What guiding principle: use every reasonable means to reduce unnecessary exposure to their patients, their staff, and themselves?

Dose limitation

What guiding principle ensures that no individuals excluding the patient are exposed to unacceptably high doses?

True. 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.

T/F. Dose limitation does not apply to patients.

Before conducting any type of radiographic examination, clinicians should complete a comprehensive clinical examination and patient assessment, with consideration of the patient's oral and medical histories, including previous radiographs, as well as the patient's specific oral disease risk

What should occur before radiographs are taken?

Digital

What should be used: digital or film imaging for a lower radiation exposure?

If conventional film is used, only E-speed or F-speed film shall be used because they require substantially lower patient radiation exposure compared to D-speed film.

If you have to use film instead of digital, what film should you use?

shortest: 8 inches

longest: 12 inches

*With a longer source-to-skin distance, the x-ray beam is less divergent, reducing the exposed tissue volume

*The use of a longer source-to-object distance also decreases image magnification

What is the shortest and longest source-to-skin distance allowed? What is the benefit of a longer source to skin distance?

Less magnified so is its more true to size

If we have a longer source-to-object distance, is the image magnified or more true to size?

less divergent, reducing

With a longer source-to-skin distance, the x-ray beam is less convergent/divergent, reducing/increasing the exposed tissue volume.

Rectangular collimator decreases the radiation dose by up to fivefold as compared to a circular one

Which is better at decreasing the radiation dose: rectangular or circular collimator?

Open

Should the PID be open or closed at the end?

circular (follows the shape of the PID)

Do we use rectangular or circular collimation at SIU SDM?

Low-energy photons, which have little penetrating power, are absorbed mainly by the patient and do not contribute to the information on the image. The purpose of filtration is to preferentially remove these low-energy x-ray photons from the x-ray beam. Filtration results in decreased patient exposure with no loss of radiographic information.

What is the overall goal of filtration of the x-ray beam?

50-70 kVp: 1.5 mm aluminum

Greater than 70 kVp: 2.5 mm aluminum

For 50-70 kVp we use _______ aluminum. Greater than 70 kVp _________ is required

there is no rationale to shield the gonads from radiation during diagnostic radiography.

Do we need to shield the gonads from radiation during diagnostic radiography?

- No.

- Shielding does not protect against internal scatter radiation, and it was found that compliance with other guiding principles of radiation safety in particular, rectangular collimation decreases thyroid dose from the primary beam by 50%.

Because the thryoid gland is susceptible to radiation, do we need use thryoid collars?

increased, increased

*due to more photons staying inside the patient

At lower kVp, the patient radiation dose is _________, but the image contrast is __________.

decreased, decreased

*more photons go through the patient and interact with the sensor

At higher kVp, the patient radiation dose is __________, but the image contrast is also ____________.

- shielding design

- barriers

- distance

- position

- person dosimetry

What are some of the personnel protections that follow the ALARA principle?

When barrier protection or shielding is not available for intraoral imaging, the operator shall stand at least 2 m (6 feet) from the tube head and out of the primary beam path.

If barrier protection is not available, how far should the operator be from the tube head and in what general position from the primary beam path?

Primary barriers such as walls or mobile lead barriers provide the most effective method to protect the operator from primary and scattered radiation

What is the most effective method to protect the operator from primary and scattered radiation?

90-135 degrees to the central ray of the x-ray beam

What angle should the operator be from the X-ray beam?

False. The operator should never hold films or sensors in place

T/F. If the patient is having a hard time with the sensors, the operator should hold the sensor in place.

Primary beam as it exits the patient (dont stand 180 degrees from the x-ray tube)

What is the position of maximum exposure when giving an X-ray?

Backwards 90-180 degrees from the primary bream as it enters the patient

What is the position of maximum scattered radiation?

90-135 degrees to the central ray of the x-ray beam

What is the area of minimum exposure when giving an x-ray?

Secondary protective shielding is offered in the form of a backscatter shield. This is incorporated into the device at the end of the collimator ring and provides an operator protective zone, where scattered radiation is negligible.

For handheld portable x-ray units, what is used to minimize exposure to the operator?

For optimal operator protection, the device must be held in a horizontal position, oriented perpendicular to the operator, and with the backscatter shield placed close to the patient and parallel to the operator

For handheld portable X-ray units, how does the unit have to be held to minimize exposure to the operator?

- should be considered for workers who are likely to receive an annual effective dose in excess of 1 mSv (most are not close to this, typically 0.2 mSv)

- should be provided for known pregnant occupationally exposed personnel

When should personal dosemeters be used?