Week 4 Flashcards
What are the two types of shielding for x-ray machines ?
source shielding
structural shielding
What is sources shielding?
refers to the lead shield in which the x-ray tube is housed
What is structural shielding?
refers to the shielding around the room
What are the three things that structural shielding is designed to protect?
useful or primary x-ray beam
leakage radiation
scattered radiation
What is leakage radiation?
This is all of the radiation that escapes from the machine, except for the useful radiation (from the beam itself)
What is scattered radiation?
A type of secondary radiation that results from the primary/ useful beam hitting an object and being deflected
Is the x-ray beam polyenergetic or monoenergetic and why?
polyenergetic because it has a broad range of energies
things such as anti-scatter grids remove low energy x-rays
For the RT’s-calculation of structural shield thickness - primary beam. What do the 5 symbols in the equation mean?
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
The amount of scattered radiation depend on?… (what four things)
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.
What is the scattered distance?
The scattered distance is the distance of the patient (scatterer) to the RT
What is the primary distance?
This is the distance from the source to the patient plus the distance from the patient to the RT
What are the two assumption that we make when calculating the scattered radiation dose?
- for x-ray energies below 500kVp, the energy of the scattered radiation is the same as the useful primary beam
- For x-ray energies above 500kVp the energy of the scatter radiation is 500kVp