Ionizing radiation hazards

Question 1

CT exposure vs x ray exposure doses

Answer 1

5-20 fold more exposure from CT.

Question 2

Contraindications for ionizing imaging

Answer 2

PREGNANCY. All women are pregnant until proven otherwise.

Question 3

Advantage of Cone beam CT over conventional CT

Answer 3

Cone beam uses about 10 times less radiation than conventional and has the same clarity.

Question 4

Types of radiation damage

Answer 4

direct and indirect -
Direct: the radiation directly damages the DNA
Indirect: radiation generates free radical in water, which react with DNA and damage it, adducts.

Stochastic and non stochastic
Stochastic effects: There is no dose threshold, but the probability of the effect linearly increases with increasing dose

Deterministic/Non-stochastic: There is a dose threshold, before the threshold the probability is none/almost none. After threshold the probability of radiation damage rapidly becomes 100%

Question 5

What factors can increase radiosensitivity?

Decrease it?

Answer 5

Increasing sensitivity:
Increased dose rate
High LET radiation

Radiosensitizers:
DNA antimetabolites
Metronidazole

Decreasing factors:
Sulfur

Question 6

Severe effects on early embryogenesis

Answer 6

embryonic death at very low dose levels, teratogenic, carcinogenic effects.

Question 7

What causes the biological effects of radiation damage

Answer 7

ABSORPTION

especially absorption by DNA

Question 8

How are the effects of radiation classified

Answer 8

Classified based on the timing of events

Physical interactions - immediate, excitation or ionization reactions

Physico chemical interactions - DNA damage, breaks

Biological Response - Apoptosis/mutations

Medical effects - radiation burns, cancer, teratogenesis, hereditary diseases

Question 9

Highest, medium, low sensitivity tissues to radiation

Answer 9

High: rapidly dividing cells
Spleen
Thymus
Bone marrow
Testis/Ovaries
Eye lens
Lymphocytes and lymph nodes

Medium:
Skin
GI tract
Organs

Low:
Muscles
Non-marrow bones
CNS

Question 10

Acute radiation effects

Answer 10

Cutaneous burns, dermatitis

Bone marrow syndrome/suppression,

• at doses of 0.7- 10 Gy
• can cause lethal bleeds and infections

GI syndrome

• at doses beyond 10 Gy
• Severe, highly lethal. Irreparable necrosis of the GI tract.
• death in 2 weeks

Cardiovascular syndrome
- doses beyond 50
- Death in 2 days
- circulatory collapse and cerebral edema due to widespread vasculitis
CNS syndrome

Question 11

Radiation dose limits

Answer 11

1 mSv per year effective dose, 20 mSv a year for occupational exposure

15 mSv year equivalent dose to the lens of the eye

Equivalent dose to the skin over 1 cm2.
50 mSv per year

Question 12

What is the units of 1 Gray

and

sieverts.

Answer 12

1 gray = 1 Joule/kilogram

Sieverst are the Equivalent dose, adding a conversion factor for the type of radiation that increases the damage

1 Gy of alpha is much more damaging than 1 Gy of Gamma.

1 gy gamma radiation = 1 Sv equivalent dose

1 gy alpha = 20 Sv equivalent dose.

Question 13

What is 1 mSv in laymans terms

Answer 13

the average accumulated backround radiation for an individual in 1 year.