Michael Tallhamer, MSC, DABR
We use this workflow all the time for SRS/SRT/SBRT and other treatment types that use CBCT imaging with a couch centering in order to monitor the patient during imaging to make sure they do not move before, during, or after imaging and before applying the shift.
When couch centering is anticipated during imaging for an SRS/SRT/SBRT type of case (or any type of case for that matter) we create a “centering” field during the patient import in the Record work space.
You can either re-import the DICOM structure set into that field and re-import the ROI that you had drawn on the initial imported surface (i.e. from the ISOCENTER FIELD) or leave the field blank with no surface and ROI. If you choose, as we do, not to import the DICOM surface again you will have to draw an ROI on the fly in the treatment work space before monitoring the patient for motion during CBCT imaging.
During SRS treatment we will setup to the DICOM surface in the setup field (i.e. ISOCENTER FIELD) then once we are at zero offset from the DICOM (or really really close) we take a reference image to zero out at the setup position. We then start the CBCT procedure which will require the couch centering. Center the couch and switch to the centering field you created during import from above. At that point we take a reference image under the “centering” field and draw a quick ROI to monitor for patient motion before during and after imaging.
Once the CBCT is complete and the shifts are determined through fusion you can restore the couch (switching back to you previous reference image at the setup position) and then apply the shifts. Once the shifts are applied you can just take an additional reference image at the final position and use it for monitoring throughout the treatment. Very quick and easy