2.3.3 - Effects Of Modifying Beam Parameters

Kilovoltage beams can be modified in several ways.

Accelerating Voltage

The accelerating voltage refers to the voltage applied between the cathode and anode. As it increases, the energy gained by electrons passing between the cathode and anode also increases. An increased accelerating voltage leads to:

  • Increased forward direction of bremsstrahlung photons relative to the incident electron beam
  • The effective energy, mean energy and maximum energy of the beam will be increased due to a higher proportion of higher energy photons.
  • The half value layer of the photon beam will also be increased.

Beam Current

Current refers to the number of electrons passing a point in space. Beam current refers to the number of electrons passing from the cathode to the anode.

  • An increased current leads to increased particle fluence of the resulting photon beam (ie. more photons in the beam)
  • There is no change in the angular distribution or beam spectrum
  • The main effect is to alter treatment time

Other Factors

Filtration has been discussed here.