Radiation Physics & radiobiology

4 types of electromagnetic radiation?

Gamma, X-rays, visible light, microwaves, radiowaves

Velocity when concerning the electromagnetic spectrum is?

Constant

How is frequency and wavelength related?

Inversely related.

3 Components for graphing the spectrum?

• Energy

• Frequency - cycles per second (hertz)

  • Wavelength - Distance between two wave crests (cycles/sec)

What are the 3 types of electron-target (In the tube) interactions?

• Heat

• Characteristic x-rays

• Brems x-rays

How is bremsstrahlung radiation formed?

Projectile electron passes the nucleus of target atom, slows down, changes course & leaves with reduction KE.

How is characteristic radiation formed?

Projectile electron collides with inner-shell electron, removed from target atom = Ionized.

Outer-shell fills vacancy for inner-shell = x-ray emission

What x-ray interactions happen in the body?

• Photoelectric

• Compton

What is attenuation?

Absorption + scatter

How is the photoelectric effect achived?

X-ray interacts with inner-shell electron, ionized atom & ejects a photoelectron, x-ray is absorbed not scattered.

K-shell vacancy is filled with an outer shell electron and emits a characteristic x-ray.

How is the Compton effect achieved?

x-ray interacts with outer-shell, ejects electron and ionizes the atom.

Causes photon to change direction with less energy.

What is classical scattering?

X-ray slightly changes direction without changing its energy, a scattered x-ray occurs.

What are the 3 rules of the law of bergonie & tribondeau?

• Stem cells

• Young, immature cells

  • Highly miotic cells

What does LET stand for?

Linear energy transfer.

What does RBE stand for?

Relative Biologic EffectivenessW

What does LET measure?

The rate at which energy is transferred from ionizing radiation to tissue

What does RBE concern?

The ratio of the dose of standard radiation necessary to produce a given effect/ dose of test radiation needed for the same effect.

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What is known as the “target molecule” of a cell?

DNA

What is Target Theory?

Theory that a cell will die if target molecules are inactivated by radiation exposure.

Oxygen and LET relationship?

No O2 = Low LET

O2 present = High LET

What are the direct and indirect effects?

Direct - Ionizing event occurring on the target molecule

Indirect (most common) - Ionizing event occurring on a

distant molecule

3 Types of radiation damage to DNA

• Main chain scission (Double or Single)

• Main chain breakage

• Base damage

Top 3 most radiosensitive tissues

• Lymphocytes

• Reproductive cells

• Erythrocytes

What does OER stand for and what is it?

Oxygen Enhancement Ratio, Used to compare how much more radiation is needed to damage cells without oxygen versus with oxygen.

What does major organogenesis take place?

2-12 weeks.

Dose for spontaneous abortion to take place during the 2 week mark?

250 mGy/ 25rads

Important doses

• Cataracts = .5 Gy (500 mGy)

• Temp. sterility = 2Gy (200 rad)

• Perm. sterility = 5Gy (500 rad)

• Hematopoietic = .7-10 Gy (70-1000 rads)

• GI ARS = 10 Gy (1000 rads)

• CNS ARS = 50 Gy (5000 rads