Hi all. We have treated only n0 DIBH patients so far and because amount of field is usually 2-3 we have not had large problems with Mag going out of thresholds, which are +- 3mm exept in VRT +-2mm.
We setup the patient nevertheless inside 1mm or 1 degree accuracy in FB. We allways go to BH DICOM and if there is displacement errors in the bony structures, we try to manipulate the FB VRT reference to discuss better with the DICOM BH. We think that DICOM BH is a gold standard to ensure the patient entire correct posture where we should reach. In new BH reference (which is ment to be used may be until the end of treatment) there may be differences in the locations of the bony structures related to PTV in comparison to BH DICOM/Planning CT . If there is a systematic need for isocenter shift (disagreement between the surface isocenter and bony structure isocenter) we also take new BH VRT in those cases to eliminate the systematic isocenter error. In those cases we choose the BH VRT from the day where patient is in good position (distance between vertebra and sternum, position of the arm, rotation of the vertebra and roll seen in the AP/LAT setup images is at least inside IGRT tolerances, rather precise). What do you think about this our way to think?
Ellen and others. How do you operate with AlignRT in the cases where you have noticed that there is too much error between vertebra and sternum in LAT image and patient needs to take more or less air into lungs? The other guestion, have you though about the situation when you are correcting VRT isocenter based on LAT setup images. It may disturb the accuracy of the distance between vertebra and sternum, in other words the right amount of how much patient takes air into lungs if the procedure of the couch shift is not done correctly?