SGRT Forum

Hi, I would like to ask a question about the need of redoing CBCT during DIBH delivery of liver SBRT.

when treating left breast patients with DIBH sometimes we may need to make a slight adjustment along longitudinal and/or lateral in order to coach patient into the desired DIBH position. In some situations one may need to readjust patient position at free breathing first then check DIBH again. Those operations are acceptable for breast pt because the surface position is directly correlated with the tumor position.
However, for treating other sites like abdomens and lung, doing so would override the patient position based on IGRT.
I wonder how your hospitals are doing in this situation. What tolerance may you allow to make table adjustment based on Alighrt before another IGRT is needed?
Thanks/An

hi
my feeling is that as long as you have done a CBCT, and reference captured at that moment you don't need to repeat the CBCT. I suppose if the move was v large then you may wish to - whether you have SGRT Or not

Josh

The following is the short version of our first EEBH Liver SBRT treatment process.

1. Set up the patient in the FB position and coach them into the EEBH position.
2. Perform a partial-arc CBCT (200 degrees) in EEBH.
3. After imaging registration, shift the couch and re-reference the surface (EEBH & FB) for this session only.
4. Re-CBCT in EEBH based on the new reference surface to verify the reproducibility. If the tumor is in PTV, continue with the treatment.

I hope this is helpful!

Hello

There are few studies evaluating SGRT, SBRT and DIBH. Naumann et al used 3 mm and 2° thresholds intrafractionally https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7546313/ and created the ROI to lower thorax. Zeng et al. https://aapm.onlinelibrary.wiley.com/do ... acm2.13740 compared the accuracy between SGRT and the markers with triggered imaging, when treating gastrointestinal cancers in DIBH. They used ROI which covered both part of the bony lower thorax and abdomen. Thresholds during treatment were ± 3 mm and ± 3°. Nguyen et al https://www.sciencedirect.com/science/a ... 0398#s0080 used thresholds of +/-1 mm for the vertical value and +/-2 mm/° for the other directions during treatment, treating SBRT and SGRT lung patients in DIBH with a closed-bore gantry linac. Thanks to quick CBCT in this linac, they were able to acquire more CBCTs between the arcs, which is unpractical with C- arms linac. Their ROI in FB setup covered the entire chest while the DIBH treatment ROI contained the ipsilateral part of the thorax overlapping the isocenter. They found good reproducibility. However, as you obviously think, there may be a risk to rely on SGRT alone when treating the targets near diaphragm https://www.sciencedirect.com/science/a ... 1623000465.

For this intrafractional imaging, I think we need more innovations from Varian. Intrafractional imaging has not developped during last years aas much as we would like. Unpractical CBCTs during treatment and limited triggered imaging or MV- during imaging https://sgrt.org/video-library/sbrt-the ... anagement/ are not yet offering reliable intrafractional control for SBRT DIBH treatments. As long as intrafractional imaging is in at this level, we may not begin to perform SGRT DIBH in SBRT routineosly. Waiting for improvements from Varian.

BR Marko