Radiation Types

Question 1

There are five ways of delivering external beam radiation therapy (EBRT). Linacs and superficial are two. List the three others.

Answer 1

Greens ray, contact, Orthovoltage

Question 2

Explain Ionising radiation.

Answer 2

Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized.

directly ionising - Direct Coulomb interactions

indirectly ionising -Release of charged particle
in the medium, then direct Coulomb interactions

Question 3

Explain non-ionising

Answer 3

any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule.

Question 4

Explain what a photon is and describe its properties.

Answer 4

elementary particle, no rest mass or rest energy,

no electric charge, travels at speed of light

Question 5

Explain the term EM radiation, and describe the electromagnetic spectrum.

Answer 5

• Energy carried by oscillating electrical and magnetic fields
travelling at the speed of light
• Wave-particle

The electromagnetic spectrum classify em radiation by their frequency or wavelength, going from high to low frequency.

Question 6

Describe the difference between atomic energy levels and nuclear energy levels.

Answer 6

Atomic energy levels- Energy levels (binding energies) of the orbital electrons (ionisation), characteristic energies

Nuclear energy levels- State of the nucleus - gamma radiation

Question 7

Explain the difference between atomic ionisation and excitation.

Answer 7

atomic ionisation

Question 8

What is general principle of the inverse square law? Explain the inverse square law for radiation.

Answer 8

Radiation from a source loses intensity as the square of the distance increases.

Question 9

What is attenuation?

Answer 9

As the x-ray beam passes through tissue, photons get absorbed so there is less energy; this is known as attenuation.

Question 10

What is the linear attenuation coefficient?


Answer 10

A measure of how well a material is at attenuating radiation

Question 11

What is the mass attenuation coefficient?


Answer 11

linear attenuation coefficient over density

Question 12

What is the difference between the linear and the mass attenuation coefficient?


Answer 12

mass attenuation coefficient is independent of density

Question 13

What are the three main photon interactions with matter?

Answer 13

• Photoelectric effect
• Compton scattering
• Pair production

Question 14

Pair production

Answer 14

photon interacts with electric field of nucleus, and absorbed, this absorption creates positron and electron. The positron is immediately annihilated by an electron, this creates two photons separated by 180 degrees and have equal energy of 0.511 Mev . Increasing with increasing energy as above 1.02 Mev, increases with increasing atomic number.


Question 15

Compton Scatter

Answer 15

outer shell, some energy transferred, electron ejected, photon scattered. Probability Decreases with increasing energy, not dependent on atomic number 


Question 16

Photoelectric

Answer 16

interaction with inner shell electron, photon absorbed and electron ejected. Photon energy must exceed binding energy. Probability decreases with increasing energy, increases with atomic number. 


Question 17

How are the three main interactions included in the total mass attenuation coefficient?


Answer 17

all added together and divided by density

Question 18

Which interaction is aimed for and ideally maximised in diagnostic radiology? Why?

Answer 18

Photoelectric effect, as it is mainly responsible for producing contrast in diagnostic imaging

Question 19

Which interaction is dominant in radiation therapy?

Answer 19

Compton scattering

Question 20

What process has the same outcome as pair production? Which type of imaging is associated with this process?


Answer 20

Beta decay - PET imaging

Question 21

What is the linear energy transfer coefficient?

Answer 21

The measure of the probability of energy transfer

Question 22

What is the mass energy transfer coefficient?

Answer 22

Linear transfer coefficient divided by density.

Question 23

What is the linear energy absorption coefficient?

Answer 23

The measure of the probability of energy absorbed

Question 24

What is the mass energy absorption coefficient?

Answer 24

linear energy absorption occurring/ density

Question 25

Explain the function of a filter on a kilovoltage X-ray beam

Answer 25

filter out low energy x-rays, producing a harder beam and less unwanted dose within the pt.

Question 26

Draw the X-ray spectrum both with and without the filter

Answer 26

With filtration peak shifts to the right and is lower, finishes at the same point but starts more to the right.

Question 27

Describe the type of filter used on an orthovoltage X-ray tube.


Answer 27

added metal sheet, they may use aluminium, copper or tin or combination