SGRT Forum

I'm just wondering how people are approaching planning the DIBH/FB plans with Align RT. I understand the logic of setting up to the FB contour and then switching to DIBH contour in breath hold. However I feel like I'm missing something in how these two scans are linked. With our current method these structure sets are not registered to each and have different isocentres so I'm not sure how we are comparing like for like on set. I would appreciate your insights on this. We are using Eclipse and don't currently have the Gate CT system.

Hi Conor, the FB scan is just to get the patient into an approximate position prior to BH. We place the isocentre at the centre of the PTV on both scans, but both will have different coordinates based on the nature of the scans. Ideally, when the patient is set up in FB and enter BH all deltas will be in tolerance reproducing what happens at CT, but this is not usually the case and requires some adjustment for Lat and Long directions.
If as you say you have completely different isocentre locations, you could use the FB to initially position the patient, enter BH and make the adjustments and when the patients exhales capture a new reference for the FB setup which should be 'below' the BH setup going forward. Hope this helps.

Hi, just to be sure i understand your workflow.

You are using the same patient set up in the CT room and you are performing a FB scan and then a DIBH scan.

Then you export the FB and DIBH scans in eclipse, you optimize 2 plans (thats why you say 2 isocenters) and then you compare the dosimetries to decide if the DIBH plan is best for your patient.

In eclipse your 2 scans should be in the same frame of reference and the spine of the 2 scans should be matched. Right? If so, all you have to do is copy the BODY structure of the FB scan on your DIBH structure set and rename it FB BODY or something like that. That way you will have 2 Bodies, one used for the dosimetry (the DIBH one) and one coming from the FB scan.

Once you export your plan on VRT you will have 1 isocenter coming from the plan but you will create 1 FIELD for the FB contour and 1 FIELD for the DIBH contour. Both fields will be under the same isocenter course. That way during the treatment you can position your patient in FB and then treat in DIBH.



Karim

Alternatively, you can take your two CT scans as part of the same study so they are DICOM linked when they come into Eclipse (so you don't have to register them based on spine). Then you can export both the freebreathing and DIBH structure sets to AlignRT, and pull each external contour into its appropriate field.