SGRT Forum

I would like to ask the question are people doing quality assurance other than the plate calibration. What I am particularly interested in is a technique that we can do on a morning run up to assure that the beam is turning on and off when we think it is and that the correct amount of radiation is being delivered. Hence checking the communication of AlignRT with the truebeams and whether there is a latency.

Thanks

Nicola,

We perform an extended morning warm-up using two DICOM RT plans on the Varian TrueBeam. We have scanned a cube phantom with both a central isocenter and an offset isocenter (very common TG-142 imaging setup). This can be the isocenter calibration cube that comes with the system (5 offset positions) or another cube like the Standard Imaging MIMI phantom. An "Imaging" plan with your TG-142 kV/MV/CBCT coincidence images can be created at the central isocenter location while what we call the MMI Verification Plan containing a single AP field with 100-200 MUs can be created at the offset isocenter location. Once the plans are created you can push these to both AlignRT and to the TrueBeam to be used in file mode (DICOM RT mode on the old 4DITC boxes). After importing the plans into AlignRT open the MMI Verification plan in the Treatment workspace and add a fake 10 degree couch kick under the couch kick dropdown which will be used to test the gating of the beam later and close out.

If the systems are connected through MMI (and I assume Response for an Elekta) opening up the plan on the TrueBeam will automatically prompt you to open the same patient on AlignRT (software connectivity tests from TG-147).
Load up the Imaging plan and open the patient on AlignRT when prompted to.
You can then go into the room and setup the cube phantom of your choice to the offset isocenter location used for the MMI test (NOT the central isocenter location) and turn on monitoring for the same isocenter in AlignRT using the DICOM surface from the MMI plan and check for setup accuracy of 1mm or less (static localization test from TG-147).
You can then take a reference image of the phantom in that setup location under the same plan for use later in the MMI check and check the ROI propagation for proper transfer to the new reference image (software functionality testing from TG-147).
Take a treatment capture and look at SSD and surface stats from the Surface tools window and compare against known reference values (software functionality testing from TG-147).
When all that is done in the room (or from the control room) you can then CBCT the phantom watching the real-time deltas for “jumpiness” during the CBCT checking to make sure severe obstruction (Head and all imaging arms out during full arc rotation) doesn’t affect the delta readouts (obstruction testing from TG-147)
Once the CBCT is complete move the phantom remotely from the offset isocenter to the central isocenter using the TrueBeam console. (check shifts against known values for TG-142)
As you move the phantom watch the real-time delta values update on AlignRT and make sure they update in real time to within 0.5mm of the expected values from the CBCT shifts as you move the couch (dynamic tracking accuracy from TG-147)
Once the shifts are complete switch to the central isocenter plan in AlignRT and verify the DICOM surface against the final positioning of the phantom from CBCT is within 1mm (static localization accuracy end-to-end from TG-147)
Complete the TG-142 kV/MV/CBCT coincidence images and record the values as you probably are already doing while watching the deltas on Align RT as the imagers continue to obstruct the phantom
Once complete close the Imaging plan on both AlignRT and on the TrueBeam
Open the MMI verification plan on both the TrueBeam and on AlignRT when prompted
Select the previous reference image you took during step 4
Mode up and select the Couch Move button to check the MMI couch control functionality (software functionality testing from TG-147).
Apply the Couch move shifts on the TrueBeam and watch for the delta values to update in real-time (connectivity checks from TG-147 and again a dynamic tracking accuracy from TG-147)
After completing the couch move check of the MMI interface turn on the Gating in AlignRT and verify the interlock disappears from the TrueBeam (connectivity checks from TG-147)
Deliver the AP field
During delivery select the fake 10 degree couch kick you created during import and ensure the beam is gated on the TrueBeam.
Go back to the couch 0 setting and ensure that the beam resumes on the TrueBeam
Repeat (18 and 19) 3 times and then allow beam to complete
Check MU1/MU2 and backup counter on the machine for complete delivery
Daily latency checks can be based on observation or if you really want to tease it out of raw data you can setup AlignRT to export the real-time deltas to a file and review the raw data and timestamps.