L 6: Quality of x-ray beams

Question 1

Beam Hardening

Answer 1

Increase of average beam energy with higher energy

Question 2

Attenuation

Answer 2

• Decrease in beam energy as it passes through matter
• Main concept for photons
• Charged particles do not undergo attenuation but undergo slowing and stopping

Question 3

Intensity

Answer 3

• How much dose a beam can give
• Fluence, # of particles

Question 4

Penetration

Answer 4

• How deep a beam can go
• Energy, beam quality

Question 5

Beam Quality

Answer 5

Measurement of photon beams penetration capacity

Question 6

Beam Quality for diagnostic, superficial & orthovoltage beams is defined by

Answer 6

kVp
HVL
FIlteration
* If all above options are there, pick HVL

kVp = peak voltage

Question 7

Beam Quality for mega voltage beams is defined by

Answer 7

Determined by % depth dose distribution at 10 cm depth for a 10 x 10 field in water @100cm SSD

TG-51

Question 8

HVL definition

Answer 8

It is the thickness of an absorber of specified composition to attenuate the intensity of the beam to half of its original value.

Question 9

HVL formula

Answer 9

HVL = 0.693/u

u = linear attenuation coefficient

Question 10

Tenth HVL/TVL

Answer 10

TVL = 2.3/u = 3.3 x HVL

Question 11

Effective Energy

Answer 11

kV beams based on HVL
MV beams based on PDD

Question 12

Shielding aganist Neutrons

Answer 12

Hydrogen rich materials like concrete

Question 13

Output of X-ray tube

Answer 13

Increases with increase in voltage

Question 14

Monoenergitic beam

Answer 14

HVL is constant

Question 15

Narrow energy beam

Answer 15

Very close HVLs

Question 16

Largest increase in HVL with a low energy filter placed in beam

Answer 16

Energy spectrum that has the largest proportion of low energy beams.

Question 17

Narrow beam geomtry

Answer 17

measure primary radiation only

Question 18

f-factor/f-med

Answer 18

• Also called roentgen to rad conversion factor = 0.876
• function of both medium composition and photon energy