This step is optional. It is a set of scans to obtain an overview of the system before the complete queue measurement for annual commissioning or QA tests. The results are also used to check whether the location of CCU is far enough away from the LINAC by detecting the scattered radiation.
3D Phantoms: Blue Phantom2 or SMARTSCAN Phantom for Photons
The set of preliminary scans are scans for inline/crossline profiles and depth dose for the minimum and maximum energies (e.g., 4 MV and 15 MV, respectively) configured at the LINAC:
-
4 MV, 300 mm × 300 mm, 100 mm depth, inline
-
4 MV, 300 mm × 300 mm, 100 mm depth, crossline
-
4 MV, 300 mm × 300 mm, depth dose (0 mm - 310 mm)
-
15 MV, 300 mm × 300 mm, 100 mm depth, inline
-
15 MV, 300 mm × 300 mm, 100 mm depth, crossline
-
15 MV, 300 mm × 300 mm, depth dose (0 mm - 310 mm)
-
4 MV, 100 mm × 100 mm, 100 mm depth, inline
-
4 MV, 100 mm × 100 mm, 100 mm depth, crossline
-
4 MV, 100 mm × 100 mm, depth dose (0 mm - 310 mm)
-
15 MV, 100 mm × 100 mm, 100 mm depth, inline
-
15 MV, 100 mm × 100 mm, 100 mm depth, crossline
-
15 MV, 100 mm × 100 mm, depth dose (0 mm - 310 mm)
(See a practical procedure example in Step 4, Workflow of the Baseline Measurements Page)
2D Preliminary Queue for Blue PhantomCOMPACT for Photons
The preliminary queue for Blue PhantomCOMPACT includes the following 6 scans:
-
Energy (mean energy of the machine)
-
Field sizes
-
Reference field size (i.e. 100 mm × 100 mm)
-
Maximum field size (i.e. 280 mm × 280 mm)
-
-
Scans type for each field size:
-
100 mm depth, inline (if allowed from the servo orientation, in case of Blue PhantomCOMPACT)
-
100 mm depth, crossline (if allowed from the servo orientation, in case of Blue PhantomCOMPACT)
-
depth dose (0 mm - 310 mm)
-
Preliminary Scans for Electrons
The preliminary queue for electron scans includes the following scans:
-
One PDD for each energy that is used in the queue
-
Field size is the first item of the queue, if a queue is available, or the reference field size (i.e. 10 cm × 10 cm), if a queue is not available.
-
Scan-length
-
0 - 35 mm if E < 6MeV
-
0 - 60 mm if 6 MeV ≤ E ≤ 9MeV
-
0 - 100 mm if 9MeV < E < 18MeV
-
0 - 140 mm if E ≥ 18MeV
-
Detection of Scattered Radiation
The scattered radiation is used to check whether the CCU electrometer is affected by the LINAC and whether the cables are damaged. The CCU location should be outside the range of unacceptable scattered radiation level.
The tolerance of scattered radiation is defined in :
Scattered radiation threshold: defines the scattered radiation detection threshold, default value: 10% of an internally rescaled profile. The scan is internally rescaled to 100% at CAX.
If the dose at the start or stop position of a profile is higher than a predefined threshold value (e.g. 10%) the status of the scan is set to suspicious.
Maximum gradient for scattered radiation detection of the profile tail: the threshold for the gradient at the profile tails in %/mm (or %/cm depending on the unit settings), default value: 0.2 %/mm. To define the gradient, two points are created which are averaged over 5 mm on each side of the profile.
If the results of preliminary scans are passed, a green checkmark appears under Summary. If the results of preliminary scans are failed, at least one scan is failed and the analysis result of each scan is displayed in the overlay, Preliminary Scans Results.
The following options are available:
-
Accept the results by clicking Accept result…, a popup dialog opens.
By clicking Yes, the preliminary scans are marked as passed. Click Close to close the overlay.
-
Redo the measurements, e.g., after modifying the equipment by clicking Close and then the Run button of Preliminary scans under Summary.
By clicking the Info icon in the Results column, the corresponding the analysis results will be displayed.