Reply To: Workflow for iso shifts between FB and BH

Forums Deep Inspiration Breath Hold Workflow for iso shifts between FB and BH Reply To: Workflow for iso shifts between FB and BH

Marko Laaksomaa

Hi 🙂

I am working as a radiotherapist at the unit which still uses tattoos for all DIBH patients, from 6 clinacs one of those AlignRT is installed. We initially setup the patient at all the fractions with couch LAT at zero with two tattoos on the sternum to check the straightness and additionally check the indexed numerical value from the fixation device (which has taken at the CT) to meet the middle reference tattoo. At the first fraction we acquire couch values and acquire a gated FB setup surface after succeeded kV/kV imaging and couch shifts, in FB naturally. On the next day we setup the patient based on the tattoos as at the first fraction (straightness+middle point to indexed value) and after that press the automatic couch shift button in manipulator to shift the couch to previously acquired values. Then we do the positional corrections based on FB RTDs and perform the small couch shifts in LNG and LAT.  We keep the couch vertical in the acquired value, but do not allow the vertical to vary more than 3 mm from AlignRT FB surface vertical either. After FB setup with AlignRT we go to BH and usually patient position is inside 1 degree and thereby accepted in BH. Sometimes we have to correct the couch in LNG (or LAT) in BH so that patient falls into BH thresholds in that direction. This may weaker the accuracy between vertebra and sternum in LNG, because either patient targets a breath hold in LNG wrongly (which has been the common case with RPM) or our FB surface/patient vertebra is in wrong coordinates in that direction in comparison to BH surface. This is under investigation:). These small couch shift corrections in LNG has nothing to do with tangential image accuracy, if the RTDs finally goes to zero in BH. In BH we take treatment capture to see the position of the arm is correct. Based on my results here, I do not see any parts where tattoos could remarkably improve the accuracy in DIBH. This can be investigated such that we position the patient ignoring the tattoos for some test patients at some point…

The succeeded FB setup is very important, and obviously happens better with the aid of SGRT than with laser setup. After that very important is also that patient takes similar kind of breath holds. This does not happen in large population easily. It would be interesting to hear more about breath hold guidance workflows, CT workflows and the depth of DIBHs from the units where everything goes just like that in DIBH. Have anyone checked the daily variation (starting points) of the LNG and VRT bars from FB situation to BH, how much they really vary inter-fractionally. I suppose in the succeeded BH they should not vary a lot if FB setup is succeeded?

Regards Marko