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

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