PET CT fusion on Pinnacle
Kevin Riddell
--
The optimist expects it to change.
The leader adjusts the sails.
~ John Maxwell
John Shakeshaft
Hi Kevin,
This process needs quite careful QA for each scanner that you use (if you are going to use this registered image data for target volume creation). Remember that if the registration is wrong, this will potentially create a systematic error which propagated all through treatment. You need to know the size of your potential systematic errors when defining your margins. So depending on your on which formalism you use, a systematic registration error of 1mm should typically add 2-2.5mm to your margins. Sub-mm registration accuracy given deformations in the patient between image sets, and in the case of MR given distortions in the image can be quite a challenge.
Some questions:
Are the datasets (PET and CT) the same length with the same field of view? This should be checked for each dataset. They usually are but sometimes data can be lost along the way. This will cause errors in Pinnacle if you use the method you describe.
Are the coordinate systems the same in both image sets? This can easily be checked by finding an anatomical point which can be identified in both datasets, placing a point on it and copying it between the datasets and checking that both copies have the same coordinates.
Rotations: If you are seeing these sorts of problems you need to be VERY careful to make sure that rotations are expressed about the same point. Small errors in rotations can create large registration errors.
The robust way to copy registrations is to use the DICOM registration object, which has been supported in Pinnacle since version 8.0. However it is not supported in all systems. It would take some pages to give a full tutorial on this here.
Best regards
John
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Pfund,John
The y translation is related to the differences in field of view. The PET is typically 70cm while it is typically 50cm for your CT. The way P3 interprets these FOV’s results in the 20cm offset. A good way to get around this is to have your PET/CT techs reconstruct the PET FOV to match the CT before they send them to P3.
John Pfund, MS
Sanford Health
Roger Maris Cancer Center
Fargo, ND
From: pinnacl...@googlegroups.com [mailto:pinnacl...@googlegroups.com]
On Behalf Of Kevin Riddell
Sent: Wednesday, February 29, 2012 6:17 PM
To: pinnacl...@googlegroups.com; meddos
Subject: [p3rtp] PET CT fusion on Pinnacle
Hi there,
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Bert Goudry
Hello,
We have seen the same problem a few years ago. And after some trial and error we came up with an answer. In fact a collegue (Steven Staelens) of the UZA (Universitair Ziekenhuis Antwerpen) came up with a solution. It seemed that it was a “small bug” in Pinnacle that causes these problems.
I will add the solution as an attachment.
The way we work is by fusing the CT-images from the PET-CT. When the fusion of the CT is done adjust the position of the PET-images by the attached protocol.
Another way of solving this problem is as mentioned before by John Pfund: Equal FOV reconstruction for CT and PET part.
Hope this will solve the problem,
Bert
____________________________________________________________________________
Bert Goudry
Dosimetrist
Universitaire Radiotherapie Antwerpen
ZNA Middelheim
Lindendreef 1
2020 Antwerpen
Belgium
bert.goudry@zna.be
____________________________________________________________________________
Bryan Murray
I will throw one more step in the process that helps me sleep at night…
After fusing the pet ct to the planning ct, add an roi that is attached to the pet ct. Auto-contour the external surface of the pet ct in the region of the planning ct (the secondary dataset will need to be set to “transverse”. Then, transfer that contour to the planning ct. Switch the secondary dataset to the pet and window/level to where you can see the outer contour of the pet. When copying the translation from the ct to the pet, the outer contour should “fit”. I like to look at this in a coronal and sagittal view as well setting the “pet ct external” to poly.
Bryan Murray, CMD
Dallas, TX