Reply To: DIBH patient set up

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Marko Laaksomaa

Hello Teddi

At the beginning of our AlignRT DIBHs we did the setup to FB DICOM surface (also in vertical) and thenĀ  switched to BH- DICOM surface and did small adjustments to the couch in SI and LAT based on patients BH. We noticed displacement errors between vertebra and sternum in both AP and SI- directions, indicating the unsuccessful breath hold level. Then also our physicists created a workflow where we do not change the couch vertical value after good BHL in the LAT image together with good FB- and BH- surfaces were found. This is because we have evaluated that the vertebra location in vertical direction remains better the same if the couch vertical is not changed daily based on FB- surface. Thereby the correct BHL, in other words the accuracy between vertebra and sternum is more reproducible. Both vertebra and sternum are locked to certain coordinates. Still the challenge has been the pitch, which I consider is the displacement between sternum and vertebra in SI- direction. This is not necessarily visible in the AlignRT and offline review evaluation has been needed to see how systematic the error is and how to correct it. I think that most of the errors nowadays comes already from the FB- setup, if the patient is setup to more tensed position and this error remains in the BH. It is often said that patient takes the BH wrong, which may be true but several pitch- errors comes already from the unsuccessful setup, which may be due to different setup conditions at the CT. Those are mostly small errors and insignificant in WB DIBH treatments, but as this pitch in SI- direction shifts the vertebra in SI- direction (and SGRT follows the surface) it may have negative influence on WBLN and mastectomy treatment realization in the lymph node area. May be fixation has something to do with this in the random error cases, butĀ  in the systematic cases I could focus on CT- workflows. Do small studies between the fixations and test it on your own how much vertebra location varies daily in vertical direction in DIBH.

Regards Marko