Radiation Biology

Direct Radiation

-X ray photon or free electron interact directly with a DNA molecule

-Extremely uncommon because the DNA itself only makes up 1% of the cells mass

Indirect Radiation

-X ray photon hits the cytoplasm (organelles)

-Results in radiolysis → can become free radicals or hydrogen peroxide molecules which can cause damage to the DNA

-More common due to the cell being made up of 80% water

What happens whn DNA is damaged?

-Base pair lesions

-Single strand breaks

-Double Strand breaks

Base Pair lesions (DNA Damage)

-Break to the DNAs base pairs (rungs of the DNA ladder)

-Easily repaired

Single Strand Breaks (DNA damage)

-Break to one side of the DNAs sugar phosphates ladder

Double Strand Breaks (DNA damage)

-Break to both sides of the ladder

-This is the least common but the most significant

-It is difficult to repair or can be mis-repaired

-It can result in cell death or mutation

Stochastic Effects of Radiation

-Random, Unpredictable, Probabilistic

-Probability of an effect occurring increases with exposure

-Severity of an effect is not affected by the dose

Deterministic Effect of Radiation

-Predictable

-Effect occur at a specific dose thresholds

-EX: cataracts, epilation, skin erythema, decreased sperm counts

Linear Non-Threshold Dose response model

-Most popular model

-No safe does (theoretically any dose could cause cancer)

Decreased Sperm count dose?

-150mGy+

Erythema Threshold dose?

-2,000Gy+

Epilation Threshold dose?

-3,000Gy+

Short Term Effects of Radiation

-Immediate, early effects

-Occur within minute-hours after exposure

-Deterministic (Dose thresholds, predictable)

Long Term Effects of Radiation

-Delayed effects

-Occur several years after exposure

-Stochastic (No threshold, probabilistic)

-EX: Cancer, genetic mutations

Exception of Long term Radiation effects?

-Cataracts (long term but is deterministic)

Somatic Effects of Radiation

-Harm to the body of the exposed person

-harm to normal cells

-Damage is not passed on

-EX: cancer, cataracts, fetal/embryo effects

Genetic Effects of Radiation

-Harm passed on to future generations (not the exposed person) through reproductive organs

-harm is to the reproductive germ cells (sperm, ova)

-DNA damage is passed on

-EX: mutations, cystic fibrosis, heart disease

3 Possible Effects of Reproductive Organs exposure to radiation

-Cancer

-Infertility

-Genetic Effects

3 Categories of Genetic Effects

-Mendellian Diseases

-Chromosomal Diseases

-Multifactorial Diseases

Acute Radiation Syndrome (ARS)

-Result of whole-body high dose exposure

-Deterministic

-Early effect (occurs soon after exposure)

-Often results in death due to body system responses

3 Types of System Responses to ARS

-Hematopoietic Syndrome (1 to 10 Gy)

-Gastrointestinal Syndrome (6 to 10 Gy)

-Cerebrovascular Syndrome ( over 50 Gy)

Hematopoietic Syndrome

-Begins to occur at doses >1 Gy

-Causes blood cell death

-Leads to anorexia, fever, lethargy

-Death due to infection or hemorrhage within 1 to 2 months

-Some may survive

Gastrointestinal Syndrome

-Begins to occur at doses of >10 Gy

-Causes destruction of the GI tract

-Leads to diarrhea, dehydration, electrolyte imbalance

-Death due to dehydration within 9 to 10 days

-Not expected to survive-

Cerebrovascular Syndrome

-Begins to occur at doses >50 Gy

-Lead to convulsions and coma

-Most severe response

-Death occurs within hours to days

Phases of Progression of ARS

-Prodromal phase

-Latency phase

-Manifest Illness

Prodromal Phase

-Body’s intial reaction to high doses of exposure

-Symptoms occur within hour - days, subside within a few days

-Symptoms: anorexia, nausea, vomitting, diarrhea L

Latency Phase

-Symptoms appear to have resolved

-Length of phase inversely related to dose (lower dose = last longer, higher dose = phase could even be eliminated)

Manifest Illness

-Full onset of systemic illness

-Severity and duration dependent on does (higher dose = more severe)

LD 50/60

-The lethal dose that will kill 50% of the human population within 60 days

What is the LD 50/60 for Humans?

-3 to 4 Gy

Protection from radiation

-Minimize time of exposure (Time)

-Maximize your distance from source and patient (Distance)

-Shield yourself (sheilding)

Aprons And thyroid shield require a minimum of ___ for sheilding?

-0.5 mm Lead

Glasses require a minimum of ___ for shielding?

-0.35mm of lead

Gloves, protective curtains, and bucky slot covers require a minimum of ___ for shielding?

-0.25mm of lead

Structural Shielding:

-Primary barriers should be 1/16” of lead (where the beam is directed)

-Secondary barriers should be 1/32” of lead (where beam is not normally directed)

Half Value Layer

-The shielding required (width of material) to reduce a beams intensity to 50% its original value

1 HVL decreases intensity to?

-50%

2 HVL decreases intensity to?

-25%

3 HVL decreases intensity to?

-12.5%

Personal Dosimetry Devices

-Used to track radiation dose to occupational workers

-X-rays interact with device detector inside and is used to convert to units of measure (mGy, mSv)

Equipment Survey Devices

-Used to ensure proper radiation output of X-ray machines/equipment

-Check that mA and kVp match what are selected at the console

-Used to protect patient

Enivronmental Survey Devices

-Used to monitor radioactive contamination and x-ray transmission into occupied areas

-Used for occupational and public safety

-Checks how much radiation passes through the lead walls in exam room

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