Chapter 9

Ionizing Radiation

- is energy capable of penetrating matter and possesses sufficient energy to eject orbital electrons along its path, thus ionizing atoms

- can have biologic effects

Benefits

______ must outweigh the risks of any diagnostic study using ionizing radiation

Sources of ionizing radiation:

- Natural (background) radiation​

- Human-made (artificial) radiation

Natural Radiation

Occurs spontaneously in nature and are not affected by human activity

Natural Radiation Forms

- Cosmic radiation (the sun)​

- Naturally occurring radioactive substances (radium and uranium)

Human Made Radiation

- More commonly called X-rays​

- are a form of electromagnetic radiation that travels at the speed of light

Three Things Needed for an X-Ray

- A source of electrons​

- Means to rapidly accelerate the electrons​

- Means to rapidly stop the electrons ​

- All are met within the x-ray tube (vacuum)

Source of Electrons for X-Ray Production

- Cathode - negative ​

- Filament heats up when current (milliamperage) is applied ​

- Thermionic Emission

Thermionic Emission

- emission of electrons from a heated source

Acceleration for X-Ray Production

- Potential Difference ​- higher kVp makes this higher

- Kilovoltage Peak (kVp)

Deceleration for X-Ray Production

- Electrons will strike the target (Anode) surface ​

- This produces x-ray photons

X-Ray Tube

consists of:​

- Cathode (-)​

- Anode (+)​

- Glass Envelope​ (vacuum)

X-Ray Beam

- is heterogenous

- the one that leaves the tube and heads towards the patient is known as the primary one

- can undergo three possible paths

Three Possible Paths of the X-Ray Beam

- The photons can be totally absorbed​ (absorbed radiation)

- The photons can interact with matter and scatter ​(scatter radiation)

- The photons can pass through matter unaffected (remnant radiation)

5 Interactions with Matter

- Classic coherent scattering​

- Photoelectric interactions​

- Compton scattering​

- Pair production​

- Photodisintegration

2 Interactions with Matter Most Important in Diagnostic Radiography

- Photoelectric interactions​

- Compton scattering

Coherent Scattering

- Involves very low-energy X-rays.​

- X-ray interacts with the atom as a whole.​

- No ionization occurs.

Photoelectric Interaction

- Occurs within the diagnostic X-ray energy range.​

- The incoming X-ray photon is completely absorbed by a collision with an inner-shell electron.​

- Responsible for the largest contribution to patient exposure

- one of the most important in diagnostic imaging

Compton Scattering

- An incoming photon collides with an outer-shell electron​

- Most occupational exposure is from Compton Scatter

- one of the most important in diagnostic imaging

system of units

To quantify the amount of radiation a patient or occupational worker receives, a _________ has been developed

SI

The _____ units were officially adopted in 1985​

(Système International d'Unités, or International System of Units)

Exposure Measurements

- radiation in the air ​

- Measures exposure in air and is not used to express absorbed dose to individuals​

- Not a measure of absorbed exposure

Exposure Unit

C/kg

Air Kerma

- movement the radiation has ​

- Measures the transfer of kinetic energy to tissue or air. ​

- Replaces the traditional unit of Exposure

Air Kerma Unit

Gray (Gy)

Absorbed Dose

- the patient's dose of exposure ​

- Measures the amount of energy absorbed in any tissue

- is the radiation energy per unit mass of absorbing medium. ​

- Depends on the type of absorbing tissue

Absorbed Dose Unit

Gray (Gy)

Absorbed Dose Air Unit

Gya

Absorbed Dose Tissue Unit

Gyt

Equivalent Doses

It is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation

Equivalent Dose Unit

Sieverts (Sv)

Effective Dose

- used for occupational exposure ​

- Unit of dose equivalence​

- Accounts for the overall risk of exposure

- Product of Absorbed Dose (Gy) x QF

Effective Dose Units

Sieverts (Sv)

Effective Dose

- Accounts for different types of radiation (Alpha, Beta, X-ray, gamma) and their biological effects​

- Referred to as a quality factor (QF)

Quality Factor

_______ of X-ray is 1, therefore 1 Gy of X-ray exposure equals 1 Sv of dose equivalence

activity

The measure of the rate at which a radionuclide decays is referred to as _______

Becquerel (Bq)

- is the unit of quantity of radioactive material, not the radiation emitted by that material

- This unit is commonly employed in nuclear medicine and radiotherapy​

One becquerel

_______ is the quantity of radioactivity in which a nucleus disintegrates every second (1 d/s = 1 Bq).​

Unit of Radioactivity

Becquerel (Bq)

Standards of Exposure

- are regulated by the FDA and its Center for Devices and Radiological Health (CDRH).​

- Receives advice from The National Council on Radiation Protection and Measurements (NCRP)

Effective dose

________ limit recommendations have been set to minimize the biological risk to exposed persons.

ALARA

An individual's dose should be kept as low as reasonably achievable

50 mSv

The annual whole-body effective dose limit for the occupational worker is ______

1/10

General public exposure is kept to ____ of occupational exposure

Two theories when it comes to exposure:

- Non-threshold

- Risk versus benefit

Non-threshold Theory

no amount of radiation is safe

Risk Versus Benefit Theory

the benefit of the exam must outweigh the risk of potential biological damage

Cumulative Effective Dose Limits

10 mSv x Age

Lens of Eyes Equivalent Dose Limits

150 mSv

Skin, Hands, and Feet Equivalent Dose Limits

500 mSv

Public Continuous or Frequent Exposures Effective Dose Limit

1 mSv

Public Infrequent Exposures Effective Dose Limit

5 mSv

Public Annual Lens of Eyes Equivalent Dose Limit

15 mSv

Public Skin, Hands, and Feet Equivalent Dose Limit

50 mSv

Public Pregnancy Equivalent Dose Limit

0.5 mSv monthly

Rad Students Annual Equivalent Dose Limit

1 mSv

Two classes of human cells

somatic and germ

Somatic Cells

perform all the body's functions

Germ Cells

reproductive cells

Two Major Parts of Cells

nucleus and cytoplasm

Nucleus

contains the chromosomes

Cytoplasm

- contains organelles responsible for the cell's metabolic function ​

- 80% water

Two theories of cellular irradiation damage

- The direct hit theory

-the indirect hit theory

Indirect Hit theory

- Involves the irradiation of water molecules in the cell cytoplasm and the creation of free radicals​

- *With X-rays, most of the cellular damage is the result of of this*

Direct Hit Theory

- Involves an X-ray photon hitting an important macromolecule such as DNA, causing genetic damage

Bergonie and Tribondeau in 1906

To study the cell's response to radiation, a method of classification according to sensitivity was developed by _______________

Law of Bergonie and Tribondeau

- mitotic activity and specific characteristics of each cell affected how the cell exhibited radiation damage

- ​*Rapidly dividing (highly mitotic) cells and those that are undifferentiated (no specific job) are more radiosensitive*

active division

- Cells are most sensitive to radiation during ____________, when they are primitive in structure and function​

- Examples of radiosensitive cells include the basal cells of the skin, crypt cells of the small intestine, and germ cells

repeated mitosis​

- Cells resistant to radiation, being more specialized in structure and function, do not undergo _____________

- These cells include nerve, muscle, and brain cells

What can happen to cell when exposed to radiation

- Cell death​

- Delayed mitosis - delay the cell division ​

- Altered mitotic rate

repair

- Cells can also try to ______ any damage sustained, and most recover ​

Factors that can affect cell recovery

- cell sensitivity

- type of radiation

- exposure rate

- total dose

Acute Radiation Syndrome (ARS)

- AKA radiation sickness or radiation poisoning​

- Is a serious condition caused by high doses of ionizing radiation exposure over a short period

*Stages of ARS*

- Prodromal stage ​

- Latent stage

- Manifest stage​

- Recovery or Death

Prodromal Stage in ARS

nausea, vomiting, and diarrhea

Latent Stage in ARS

symptoms subside, patient feels better but body is undergoing biological changes​

Manifest Stage in ARS

patient feels full effects - really sick now

Recovery or Death Stage in ARS

this stage depends on the amount of exposure

Three Radiation Syndromes (the total body response to it)

- Hematopoietic Syndrome (aka Blood Marrow Syndrome)​

- Gastrointestinal (GI) Syndrome ​

- Central Nervous System (CNS) Syndrome

Hematopoietic Syndrome

- occurs from receiving 2-10 Gy​ (200-1000 rad)

- manifest symptoms include Infection, hemorrhage, anemia

- cause of symptoms is the body's inability to produce blood cells in bone marrow

- mean survival is 6-8 weeks (or recovery in 6 months)

GI Syndroms

- occurs from receiving 10-50 Gy​ (1000-5000 rad)

- Manifest symptoms include massive diarrhea, nausea, vomiting, fever

- cause of symptoms is from Damage to epithelial lining of the GI system

- mean survival is 3-10 days

CNS Syndrome

- occurs from receiving 50+ Gy​ (5000+ rad)

- manifest symptoms include Seizures, coma, eventual death

- cause of symptoms is from Brain edema, intracranial pressure, CNS failure

- mean survival is only a few hours to 2-3 days

Early Effects of Radiation Exposure

- can occasionally be seen in radiotherapy patients ​

- Side effects will depend on the type and location of cancer, the dose of radiation given, and the patient's general health​

- Typically, short-term, mild, and treatable ​

- The most common early side effects of radiation therapy include fatigue, nausea and vomiting, and skin changes such as dryness, itching, blistering, or peeling

Late Effects of Radiation Exposure

- can develop over a long period of time after exposure ​

- They are not limited to only high doses of radiation, but can also be from low doses over a longer period

- Divided into 2 groups

-- somatic

-- genetic

Somatic Effects

- late effects of exposure that develop within the exposed individual ​

- causes Cataracts and Carcinogenesis

Genetic Effects

- late effects of exposure that occurs within future generations because of damage to the germ cells

Cardinal Rules of Protection

- Time​

- Distance (SID depending on the exam)​

- Shielding (use your best judgement, but some places have different opinions)

Additional Methods to Protecting the Patient

- Technique ​

- Filtration - built into equipment ​

- Collimation

Protecting the Rad Tech

- Time

- Distance - best and most effective​

*Doubling the distance will reduce radiation intensity by a factor of 4*

- Shielding - Lead aprons protect us​

--- Supposed to wear one when you do a portable x-ray, but most do not

Pregnant Student

- Very low risk to fetus if good ALARA practices are followed.​

- Dose limit for whole pregnancy term is 5 mSv.

- is provided a 2nd dosimetry badge. - wear it at the waist

- Fetal exposure estimation

Declaration of Pregnancy

- is voluntary.​

- 0.5 mSv per month applies during pregnancy​

- announcement can be revoked - and revoke after you give birth

1/10th (50 mSv)

- Any occupational worker who is regularly exposed to ionizing radiation must be monitored to determine the estimated exposure​

- Any worker who is likely to receive more than _____ of the recommended dose-equivalent limit should be monitored.

Personal Monitoring Dosimeters

- worn at the collar and OUTSIDE lead apron

3 Popular Monitoring Dosimeters

- Optically stimulated luminescence dosimeter (OSL)​

- Thermoluminescent dosimeter (TLD)​

- Direct Ion Storage (DIS) Dosimeter

Optically Stimulated Luminescence Dosimeters (OSL)

- is the most common method used to monitor personnel exposure​

- Consists of a strip of aluminum oxide, a copper filter, an open window, a tin filter, and an imaging filter​

- To determine the individual’s exposure, the aluminum oxide is exposed to a laser light, which stimulates the aluminum oxide after use, causing it to become luminescent in proportion to the amount of radiation exposure​

- The dose measurement range is from .01 mSv to 1000 Sv​

- Doses less than .01 mSv are not detectable and reported as M, or minimal

Thermoluminescent Dosimeters (TLD)

- It consists of a plastic holder containing crystals that absorb a portion of the energy they receive from radiation exposure​

- Uses lithium fluoride crystal​

- Radiation exposure causes a stored energy in the crystal, proportional to the exposure​

- Provides readings as low as 0.05 mSv

- very sensitive and most are kept at the facility for this reason

Pocket Dosimeter (DIS)

- Near-immediate readout​

- Exposure causes ionizations in gas that are collected, and the cumulative charge is stored in a computer chip​

- Requires access to a computer

According to the ALARA principle, what is the primary responsibility of a radiographer?

Maintain radiation exposure levels as low as reasonably achievable.

3 multiple choice options

Nausea is principally associated with which stage of Acute Radiation Syndrome?

Prodromal

3 multiple choice options

Which photon interaction with matter is responsible for the most dose to the patient?

Photoelectric

3 multiple choice options