RT samenvatting 1.2C
PDD and the RTT
- The RTT should be aware of the behavior of radiation and the consequences of his choices
when treating the patient.
o Energy choice
o Field size + margin that we take into account around the PTV
o Number of breams we use
- The RTT can play a role in performing quality controls/ dose measurements to our treatment
unit:
o Daily ‘radiation’ of the linac
o In vivo dosimetry
o Calibration
Dose profile measurement
- In the water tank we have a detector that we can move along the central axis of our radiation
beam.
- As we do that while our treatment machine is working we can make dose measurements
along the central axis in different depth so we can make PDD curves for all our
measurements we take.
Influences on PDD curve
- Field size (larger field, more scattering, so our PDD at the same depth increases)
- SSD absolute and relative influence
- Field shape (round, square, rectangle)
- Blockage (are there any block in our radiation field?)
- Filter ( do we use a filter?!)
- Thickness and density of the underlying layer
All these parameters have something to do with scattering.
Forward scatter
- Mainly High energy beam
- Scatter is directed in the direction of the radiation beam
Backscatter
- Lower energies we see more backscatter
- Opposite direction of our radiation beam
Scattering in field
- Scattering from the field edges in to the center of our field
!! We have a lot of scatter photons in our radiation beam that have a significant contribution to our
dose profiles.
PDD and the RTT
- The RTT should be aware of the behavior of radiation and the consequences of his choices
when treating the patient.
o Energy choice
o Field size + margin that we take into account around the PTV
o Number of breams we use
- The RTT can play a role in performing quality controls/ dose measurements to our treatment
unit:
o Daily ‘radiation’ of the linac
o In vivo dosimetry
o Calibration
Dose profile measurement
- In the water tank we have a detector that we can move along the central axis of our radiation
beam.
- As we do that while our treatment machine is working we can make dose measurements
along the central axis in different depth so we can make PDD curves for all our
measurements we take.
Influences on PDD curve
- Field size (larger field, more scattering, so our PDD at the same depth increases)
- SSD absolute and relative influence
- Field shape (round, square, rectangle)
- Blockage (are there any block in our radiation field?)
- Filter ( do we use a filter?!)
- Thickness and density of the underlying layer
All these parameters have something to do with scattering.
Forward scatter
- Mainly High energy beam
- Scatter is directed in the direction of the radiation beam
Backscatter
- Lower energies we see more backscatter
- Opposite direction of our radiation beam
Scattering in field
- Scattering from the field edges in to the center of our field
!! We have a lot of scatter photons in our radiation beam that have a significant contribution to our
dose profiles.
