How to configure the CT scan of the myQA SRS in the TPS in order to use it in myQA Patients?
This article is about the myQA SRS and myQA SRS Phantom.
If you are searching for the workflow for the MatriXX Evolution and miniPhantom or MatriXX Resolution and MiniPhantom R, please refer to theses articles:
Step 1: Acquire CT Image of myQA SRS and myQA SRS Phantom assembly
Place the device in the myQA SRS Phantom, or on a 5 cm thick layer of water equivalent material,
with an additional 5 cm thick layer on the measurement area of the device.
Place the myQA SRS in the myQA SRS Phantom and position it in the CT scanner using the alignment lasers: The CT origin can be aligned with the isocenter markings. The device is positioned in the CT scanner so that the central point of the measurement is positioned at the CT origin.
Scan the entire phantom, taking care to not scan the electronics area.
A CT scan resolution of 2.5 mm and below should be used with standard departmental scanning protocol for soft tissue (pelvis, abdomen) imaging.
Step 2: Contour and edit the structures in the TPS
Import the CT scan into the TPS.
Create an external contour of myQA SRS detector and phantom. If required, add a support
(treatment table) to the CT scan.
Perform the necessary mass density override:
- myQA SRS phantom (RW3): 1.045 g/cm3
- myQA SRS device (ABS): 1.04 g/cm3
- Detector area: it can be substituted with a homogeneous material such as water
Verify the structures against the dimensions of myQA SRS and myQA SRS Phantom. The active area of the detector sensor is 12 cm x 14 cm and the distance from the top of the myQA SRS Phantom to the detector plane is 9.5 cm.
myQA SRS (vertical profile):
Step 3: Calculate the isocenter point dose in the TPS
On the images of the myQA SRS device and phantom assembly, set a point on the plane
corresponding to the LINAC isocenter alignment marks on phantom surface and shown on both
coronal and transverse views. Label it.
Duo to artifact on the detector layer in the coronal view, you may need to adjust the window and
level of the CT to filter out the artifacts.
Create an open 10 cm x 10 cm reference field (recommended: 10 cm x 10 cm open field, 100MU) at
0° and have the system calculate the dose using a grid size of 2.5 mm or lower.
Find the isocenter plane and export this dose plane that will used for the verification in myQA
Patients. The isocenter is set up geometrically based on the depth and central pixel position in the
For cross checking, export the isocenter dose as the TPS reference dose. Insert a chamber into the phantom and measure the dose in the 10 cm x 10 cm field (Section 18.104.22.168). Compare the TPS reference dose with the measured reference dose.