Radiation Protection

A set of practice flashcards covering radiation protection principles, technical factors, shielding, fluoroscopy guidelines, and dosimetry based on lecture notes.

If kVp is increased without adjusting other factors, what happens to the patient dose?

Patient dose is increased.

According to the 15 percent rule, an increase in kVp typically requires a decrease in what?

Exposure ($mAs$).

What selection of exposure factors is considered the best method to reduce patient dose?

Selection of the highest possible kilovoltage consistent with image quality.

What two properties of the x-ray beam does kVp affect?

Quality and quantity.

In terms of x-ray beam quality, what does it represent?

$HVL$ or penetrability.

Can patient dose ever be reduced by using the highest $mAs$, $mA$, or grid ratio?

Never.

Which technical factor simultaneously affects overall image quality and radiation quantity?

$kVp$.

What combination of milliampere-seconds ($mAs$) and peak kilovoltage ($kVp$) delivers the LEAST amount of radiation to the patient?

Low $mAs$ and high $kVp$ (e.g., $100\,mAs$ and $100\,kVp$).

How does decreasing the $mAs$ affect patient dose?

Decreasing the $mAs$ decreases patient dose.

What happens to patient dose if an increase in $mAs$ is compensated by a decrease in $kVp$?

There will be an increase in patient dose.

Which technique system usually results in lower patient entrance skin exposures due to higher $kVp$ levels?

Fixed $kVp$ technique systems.

What is the effect of variable $kVp$ technique systems on patient dose?

They result in higher patient $ESE$ (higher dose) because they use lower $kVp$ and higher $mAs$.

Why is higher energy radiation with lower $mAs$ safer for the patient?

Higher energy radiation is more likely to exit the patient.

Which compensating filter is specifically used for swimmer’s and Dan-Miller’s projections?

Ferlic filter.

When is the use of specific area shielding warranted?

Anytime a radiosensitive organ or tissue is in or near the useful beam (within $5\,cm$ of the collimated field).

Name three radiosensitive organs or tissues that often require shielding.

Thyroid gland, breasts, and gonads.

At what distance from the collimated field is shielding required according to the ASRT white paper?

Within $5\,cm$.

What is the most common and most important area shielding?

Gonadal shielding.

What kind of secondary radiation is shielding primarily used to protect against?

Compton "Scatter."

List six types of shielding mentioned in the notes.

Apron, gloves, thyroid collar, goggles/glasses, moveable barriers, and gonadal shields.

Does proper collimation replace the need for shielding?

No, one does not replace the other; you need to both collimate and properly shield.

What are two primary advantages of beam restriction?

Reducing scatter radiation production and irradiating less biologic material.

What is the relationship between beam filtration and beam restriction?

There is no relationship between beam filtration and beam restriction.

How does reducing the field size affect scattered radiation?

Reducing the field size reduces the volume of tissue irradiated, which reduces scatter.

What must a technologist do to maintain image receptor exposure if a primary beam restrictor is added?

Increase technical factors (increase technique).

What are the three types of beam restriction devices listed?

Aperture diaphragm, Cones/Cylinders, and Collimator.

What is the most commonly used beam restricting device?

Collimator.

What is the purpose of the bottom lead shutter in a collimator?

To reduce penumbra along the periphery of the beam.

What is the function of the upper lead shutter in a collimator?

To reduce off-focus (stem) radiation reaching the $IR$.

What is off-focus radiation also known as?

Extra-focal or stem radiation.

What visual effect is created by off-focus radiation reaching the $IR$?

Ghosting of the patient's anatomy beyond the exposed field.

Is ghosting caused by scatter radiation?

No, ghosting is never caused by scatter.

Which generator type requires more exposure due to decreased efficiency: single-phase or 3-phase?

Single-phase generator.

Why are cylinders sometimes preferred over flare cones?

Cylinders do not flare and are better at reducing penumbra and off-focus radiation.

What is the simplest type of beam-restricting device?

Aperture Diaphragm.

Why does a collimator increase added filtration?

Due to the plastic exit portal and the silver-coated reflective mirror.

What is the function of a grid compared to a collimator?

Grids clean up scatter generated by the patient, while collimators restrict the beam to prevent scatter production.

What is the primary function of filtration?

To reduce patient skin dose.

What does filtration do to the average energy of the x-ray beam?

It increases the average beam energy (hardening the beam).

How much minimum total filtration is required for equipment operating above $70\,kVp$?

$2.5\,mm$ Aluminum equivalent.

How much total filtration is required for equipment operating between $50\,kVp$ and $70\,kVp$?

$1.5\,mm$ Aluminum equivalent.

How much total filtration is required for equipment operating below $50\,kVp$?

$0.5\,mm$ Aluminum equivalent.

What is the difference between inherent and added filtration?

Inherent is from the tube construction; added is materials like aluminum sheets placed in the beam path.

Give two examples of inherent filtration.

X-ray tube glass envelope and the x-ray tube port window.

What is the typical aluminum equivalent of inherent filtration?

$0.5\,mm\,Al$.

What thickness of aluminum equivalent does the collimator assembly typically contribute?

$1.0\,mm\,Al\,equivalent$.

What effect does a wedge compensating filter have on patient dose?

It increases patient dose (unlike tube filtration which reduces it).

Which type of compensating filter is most appropriate for an $AP$ projection of the foot?

Wedge filter.

Which compensating filter is typically used for shoulder radiography?

Boomerang filter.

What is the measurement of the total thickness of an absorber that reduces the beam intensity to half?

Half-value layer ($HVL$).

What three factors are often used synonymously with beam penetrability in questions?

$kVp$, $HVL$, and filtration.

How does adding contrast medium affect patient exposure?

It increases exposure because factors must be increased to compensate for higher photoelectric absorption.

In terms of patient positioning, which position reduces dose to the female breast during a chest exam?

$PA$ (Posteroanterior).

Which positioning approach reduces dose to the reproductive organs during an abdominal exam?

$PA$ (Posteroanterior).

How can the dose to the thyroid be reduced during a C-spine exam?

By performing Anterior obliques ($RAO$/$LAO$).

How can the dose to the lens of the eye be reduced during a skull exam?

By performing a $PA$ skull projection.

What is the best way to prevent voluntary motion?

Communication.

Why should a technologist sit at eye level with a pediatric patient?

To better communicate and walk them through the examination to reduce anxiety.

Why should a technologist be familiar with cultural norms regarding touch?

Because actions like touching can be misinterpreted by patients of varying backgrounds.

What is the sensitivity of pediatric organs to ionizing radiation compared to adults?

Pediatric organs are up to $10$ times more sensitive.

Who should be the first choice to hold a patient if needed?

An old, male relative.

According to national registry exams, who should NEVER be holding patients?

Technologists and students.

What is a "Pannis" in the context of obese patient radiography?

An adipose apron that may need to be moved for hip x-rays.

What is the alternative to using a grid for a part thicker than $10\,cm$?

Air-gap technique.

Increasing grid ratio has what effect on patient exposure?

It increases patient exposure (because $mAs$ must be increased to compensate).

How does a high-ratio grid compare to a low-ratio grid regarding scatter?

A high-ratio grid absorbs more scatter radiation.

What are the typical grid ratios found in fluoroscopic units?

$6:1$ to $10:1$.

How does moving the image intensifier closer to the patient during fluoroscopy affect dose?

It decreases patient dose.

Why does moving the image intensifier closer to the patient reduce dose?

The $ABC$ automatically decreases milliamperage as the intensity at the input phosphor increases.

What percentage of occupational exposure for diagnostic personnel occurs during fluoroscopy and mobile radiography?

Approximately $95\%$.

Which type of fluoroscopy results in lower personnel exposure because workers are not in the room?

Remote fluoroscopy.

What is the recommended dose limit for extremities per year?

$500\,mSv/yr$.

What is the most likely medical procedure to result in DNA changes in circulating lymphocytes?

Cardiac catheterization (due to long fluoroscopy times).

Which fluoroscopic feature helps reduce occupational dose by reducing beam-on time?

Pulsed fluoroscopy.

What is the purpose of the $5$-minute cumulative timer in fluoroscopy?

To alert the radiologist that $5$ minutes of beam-on time has passed.

The intensity of the x-ray beam at the tabletop of a fluoroscope should not exceed what value per $mA$ at $80\,kVp$?

$21\,mGy$ per minute.

If no optional high-level control is used, what is the maximum intensity allowed at the fluoroscopy tabletop?

$100\,mGy/min$.

If an optional high-level control ($HLCF$) is used, what is the maximum tabletop intensity allowed?

$200\,mGy/min$.

How does cineradiography frame rate affect patient dose?

The higher the frame rate, the greater the exposure to the patient.

What does $AERC$ stand for in fluoroscopy?

Automatic Exposure Rate Control.

What is the primary benefit of $AERC$?

It maintains the signal-to-noise ratio ($SNR$) to allow for higher $kVp$ and lower $mA$, reducing dose.

What does $ABC$ stand for and what does it maintain?

Automatic Brightness Control; it maintains image brightness.

What does $ATCM$ control during $CT$ procedures?

Exposure (Automatic Tube Current Modulation).

How does the position of the x-ray tube (under vs. over the table) affect personnel exposure?

Tube under the table results in much lower secondary radiation exposure to personnel.

As field of view ($FOV$) decreases in magnification mode, what happens to patient dose?

Patient dose increases.

Does patient dose increase with digital Flat-panel technology in magnification mode?

No, patient dose does not increase with digital flat-panel tech in magnification mode.

What is the advantage of Last Image Hold ($LIH$)?

It allows the radiologist to view an image without continuous radiation exposure, lowering patient dose.

What is the minimum source-to-skin distance ($SSD$) for stationary fluoroscopic units?

$15\,inches$ ($38\,cm$).

What is the minimum source-to-skin distance ($SSD$) for mobile fluoroscopic units?

$12\,inches$ ($30\,cm$).

What does a $DAP$ meter measure?

Patient dose at the level of the collimator.

Where is a $DAP$ meter located?

Between the collimator and the patient.

What is a disadvantage of the $DAP$ meter?

It measures dose at the collimator, not at the patient skin ($ESE$).

How often should a $DAP$ meter be calibrated?

At least twice a year.

Is a $DAP$ meter used for occupational monitoring?

No, it is used for patient dosimetry.

What does the ALARA concept specifically refer to in the context of the lecture structure?

Personnel protection.

What are the two types of secondary radiation?

Scatter radiation and Leakage radiation.

What is the most intense and hazardous source of radiation to shield?

Primary x-ray beam (useful beam).

The intensity of scatter radiation $1\,meter$ from the patient is approximately what percentage of the primary beam?

$0.1\%$ ($1/1,000\text{th}$).

What is the maximum allowed leakage radiation from the x-ray tube housing?

$1\,mGy/hr$ at $1\,meter$.

What is the purpose of the dielectric oil in the tube housing?

Heat dissipation.