Topics covered in this article include:
- Supported Phantoms
- Scanning for CBCT
- Varian CBCT
- Elekta XVI CBCT
- Measurements and Plots
- Recommended Tests
- Detailed Discussion of Measurements
The Catphan® Phantom supports phantoms in the Catphan line of phantoms in the 500, 600, and 700 series of phantoms supplied for radiation therapy and diagnostic imaging QA. For radiation therapy, in particular, the following phantoms are supported:
- Center of Phantom - The center of the phantom described is the pixel coordinate in the center of the phantom (in pixels).
- Rotation - Degrees of phantom rotation around the z-axis.
- Tilt - Degrees of phantom rotation around the x-axis.
- Yaw - Degrees of phantom rotation around the y-axis.
Scanning for CBCT
The automatic analysis service performs best if the phantoms are scanned according to the standard protocols laid out by the LINAC manufacturers.
- Place the phantom case on the gantry end of the table with the box hinges away from the gantry. It is best to place the box directly on the table and not on the table pads. Open the box, rotating the lid back 180°.
- Remove the phantom from the box and hang the Catphan® from the gantry end of the box. Make sure the box is stable with the weight of the phantom and is adequately counterweighed to prevent tipping.
- Use the lasers (or linac crosshairs) to make sure the Catphan® is centered on the first lateral height dot and center dot that are proximal to the gantry.
- Use the level and adjusting thumb screws to level the Catphan®. The re-check the Catphan® centering on the first lateral height dot and center dot.
- Move the Catphan® in towards the gantry so that it is aligned with the 3rd alignment dots from the front of the phantom.
- Perform CBCT scan.
Image Owl supports all CBCT tests suggested by Varian provided in their Installation Product Accectance guidelines, outlined below. Catphan® 504 and Catphan® 604 versions are automatically identified and analyzed.
The following scan modes are used to demonstrate basic CBCT operation, functionality, and conformance.
- Standard Dose Head (full fan)
- Pelvis (half fan)
Position the phantom on the front edge of the couch top, using the storage box as the holder.
Align the phantom as follows:
- VRT Axis: Wall lasers intersecting the side reflective dots on phantom
- LAT Axis: Overhead or Sagittal laser intersecting the top reflective dots on phantom
- LNG Axis: Middle of the Low Contrast module CTP515 aligned to wall vertical laser
Before continuing, rotate the gantry 360º around the Catphan® phantom to make sure there are no collision possibilities.
Scanning Test Method
|CBCT Mode||Standard Dose Head||Pelvis|
|New Patient ID||
Last Name: IPA
First Name: HEAD
Last Name: IPA
First Name: PELVIS
|Patient Orientation||Head First - Supine||Head First - Supine|
|Scan Diameter||24 cm (PA and LR axis)||30 x 30 cm (PA and LR axis)|
|Bow Tie Filter||Full Fan||Half Fan|
|Resolution||384 x 384||384 x 384|
|Slice Thickness||2.5 mm||2.5 mm|
|Topograms||Not required||Not required|
|Equipment/Tool||Catphan® phantom||Catphan® phantom|
- With the Clinac in CLINICAL mode, launch Treatment on the 4DITC and verify the PRO values (from the LVI) are displayed in the Treatment application.
- Open the test patient CATPHAN plan from the Treatment Queue, and mode up the CBCT setup field. Use DICOM RT mode and perform a Machine Override if the patient is not imported into the OIS and/or not available in the Treatment Queue.
- Close the OBI application and launch the CBCT application.
- Open a New Patient and enter a New Patient ID, using the ID names shown in the setup table for the applicable scan mode.
- Select Acquire new scan and follow the on-screen instructions to acquire the desired scan mode.
The full set of DICOM files from each scan mode can now be uploaded to Catphan® QA for analysis.
Elekta XVI CBCT
Catphan® QA includes all Catphan® tests from the ELEKTA CAT guidelines.
Automatic module identification is performed when a full phantom upload (or a set including the CTP404 module) is provided.
For partial phantom uploads (which do NOT include the CTP404), DICOM fields must be set as suggested in the ELEKTA CAT guidelines to provide automatic module identification.
|Module/Phantom||Patient ID||Study ID|
- The system has only been tested on data with 120kV, 40mA, 40ms as suggested in the ELEKTA CAT guidelines.
- For robust results, please use a reconstructed FOV that just covers the phantom, 200-300mm
TG142 Summary Data
To include TG142 summary data for CBCT in analysis reports select measurements from the Cone Beam CT reports subsection of the Monthly Imaging QA [Tg142 Table VI] section when building your template.
If you are using the Catphan® 503 phantom supplied with Elekta Linac's choose the TG142 summary data items from the ELEKTA CAT (CBCT and kV planar) reports subsection of Detailed Catphan Analysis.
Recommended Catphan 504 Tests
The recommended detail CBCT test selection for the Catphan 504 is shown below:
Recommended Catphan 604 Tests
The recommended detail CBCT test selection for the Catphan 604 is shown below:
Recommended Catphan 503 Tests
The recommended detail CBCT test selection for the Catphan 503 is shown below:
Detailed Discussion of Measurements
The detailed discussion of measurements is contained in separate help articles for each topic. Below are the direct links to those articles:
- Low Contrast
- Modulation Transfer Function (MTF)
- Slice Thickness
- Spatial Linearity