Lecture 3: radiation biology

Define radiation biology.

The study of the action of ionizing radiations on living things.

Define radiation.

Energy that travels through space and matter.

Define excitation.

Energy to transfer to a more energetic but still bound state.

Define ionizing radiation.

Has energy to completely remove an electron from an atom.

What are the 2 broad categories on ionizing radiation?

Particulate radiation

Electromagnetic radiation

What are the 5 types of ionizing radiation?

- alpha particles

- beta particles (electrons)

- neutrons

- x-rays

- gamma-rays

What are the types of particulate radiation?

- alpha particles

- beta particles

- neutrons

What are the types of electromagnetic radiation?

- x-rays

- gamma-rays

Describe alpha particles.

- large

- collide with matter (least penetrated)

- lose energy quickly

Describe beta particles (electrons).

- emitted from the nuclei of radioactive elements

- blocked by a thin sheet of plastic or metal

Describe neutrons.

- high speed

- exceptional ability to penetrate material

What is the only type of ionizing radiation that can make things radioactive?

Neutrons ( —> neutron activation).

Describe x-rays.

- produced outside the nucleus

- penetration blocked by lead

Describe gamma-rays.

- emitted by unstable nucleus of radioactive radioisotopes

- penetration blocked by lead

What is the critical target or radiation damage to the cell?

DNA

Describe the direct action of radiation damage to the cell.

- dominant process of particle radiation

- interacts with macromolecules (ex: DNA, proteins)

Describe the indirect action of radiation damage to the cell.

- interact with water in the cells to hydrolyzed and produce free radicals

- dominant process of electromagnetic radiation (x-rays and gamma-rays)

How much of biologic damage by x-rays is caused by indirect action?

~ 2/3

How does cell radiosensitivity relate to reproductive capacity?

Directly proportional

How does cell radiosensitivity relate to degree of differentiation?

Inversely proportional

Radiosensitivity is greatest for what 3 types of cells?

1) high mitotic rate

2) long mitotic future

3) undifferentiated

What tissues have high radiosensitivity?

Rapidly dividing tissues.

(Examples: lymphoid organs, bone marrow, gonads, small intestines, skin + other organs with epithelial lining like lens of eye).

What tissues have intermediate radiosensitivity?

- Growing cartilage and bone

- Vessels

What tissues have low radiosensitivity?

Established tissues.

(Examples: mature bone/cartilage, lung, kidneys, liver, pancreas, adrenal glands, pituitary gland, thyroid gland, muscle, nervous system).

Describe early or acute tissue response.

- seen in rapidly proliferating, renewing tissues (skin, mucus membranes, GI tract, bone marrow).

- happens within days to weeks

- repaired by rapid proliferation of stem cells

- often completely reversible

Describe late tissue response.

- occurs in slowly proliferating tissue (lung, kidney, heart, liver, CNS).

- takes months to years to happen

- may improve, but never reversible (ex: myelopathy, lung fibrosis)

Describe stochastic radiation effects on an organism.

- severity is independent of the dose (aka no "safe" dose) = assumes that any amount of radiation has a detrimental effect

- probability of the effect (not the severity) increases with dose

- all or none phenomenon (aka no dose threshold

Describe deterministic radiation effects on an organism.

- a certain minimum dose must be exceeded before the effect occurs (practical dose threshold)

- severity increases with dose.

What are examples of stochastic radiation effects on an organism?

- fetal exposure

- genetic damage

- cancer

What are examples of deterministic radiation effects on an organism?

- cataracts

-skin damage

When is fetal exposure most damaging? What does it affect?

- First trimester

- Affects organogenesis

T/F: radiation increases the incidence of spontaneous genetic mutations.

True.