Week 4

Question 1

What are the two types of shielding for x-ray machines ?

Answer 1

source shielding

structural shielding

Question 2

What is sources shielding?

Answer 2

refers to the lead shield in which the x-ray tube is housed

Question 3

What is structural shielding?

Answer 3

refers to the shielding around the room

Question 4

What are the three things that structural shielding is designed to protect?

Answer 4

useful or primary x-ray beam
leakage radiation
scattered radiation

Question 5

What is leakage radiation?

Answer 5

This is all of the radiation that escapes from the machine, except for the useful radiation (from the beam itself)

Question 6

What is scattered radiation?

Answer 6

A type of secondary radiation that results from the primary/ useful beam hitting an object and being deflected

Question 7

Is the x-ray beam polyenergetic or monoenergetic and why?

Answer 7

polyenergetic because it has a broad range of energies

things such as anti-scatter grids remove low energy x-rays

Question 8

For the RT’s-calculation of structural shield thickness - primary beam. What do the 5 symbols in the equation mean?

Answer 8

W= Workload in a mA min/wk
U = Use Factor- what proportion is beam pointed at wall/floor
T= Occupancy factor (T)- What proportion of time is the person going to be near the source
D= Distance in metres from the tube

Question 9

The amount of scattered radiation depend on?… (what four things)

Answer 9

1) The beam intensity incident on the scatter on the patient
2) the beam quality
3) the area of the beam at the scatterer (big beam scatters more than small beam)
4) The scattering angle.

Question 10

What is the scattered distance?

Answer 10

The scattered distance is the distance of the patient (scatterer) to the RT

Question 11

What is the primary distance?

Answer 11

This is the distance from the source to the patient plus the distance from the patient to the RT

Question 12

What are the two assumption that we make when calculating the scattered radiation dose?

Answer 12

1. for x-ray energies below 500kVp, the energy of the scattered radiation is the same as the useful primary beam
2. For x-ray energies above 500kVp the energy of the scatter radiation is 500kVp