… lately we have had couple mastectomy DIBH patients, where there has been needs to correct systematic error in the arm position. I give you one example about the arm position correction. With the FB and BH reference surfaces we have had everything in good accuracy in the images (vertebra, sternum, BHL, ribs in all directions), but the shoulder joint has been systematically daily 6-9 mm too caudally. At the setup we now positioned the arm more cranially in comparison to earlier FB reference surface (with treatment capture) and after all the FB deltas were 0, we took a new FB reference surface as a possible candidate for the upcoming setups (arm now more cranially). In the images there was 6 mm LNG error in the isocenter, but the arm position was ok (in comparison to th1 also). 6 mm couch shift was done in LNG, but we did not acquire new reference surfaces after couch shifts, because the bolus was used and setup is done without bolus. On the next day we knew that the patient posture (also arm) is good with the FB and BH surfaces that we acquired yesterday, but the LNG isocenter is not. So we did setup normally with the yesterdays FB and BH surfaces, but after that shifted the couch such that LNG delta was 6 mm out of zero in FB reference surface (shifted the couch based on that isocenter error that we had yesterday), took a new FB reference surface in that location and asked patient to take BH. When the LNG delta went that 6 mm out of zero again in yesterdays BH reference surface (as it should go), we took a new BH reference surface. In the images everything was ok!
What I want say with this is that correct arm position can individually be very important also when we want to optimize LNG isocenter accuracy in mastectomy DIBH with AlignRT. Arm position affected on isocenter even if the ROI was created such that it mostly covers the chest wall and not the surface structures around the shoulder. Interesting! It is much possible that with some of our other patient story is different. Individual adjustment and succeeding is what we have experienced anyway again with AlignRT.