Forums SGRT – Best Practice Extended distance treatments/ comp. breast treatments Reply To: Extended distance treatments/ comp. breast treatments

Marko Laaksomaa

Hi Chad

There can also be challenging situations with two -isocenters. I can give you one new example of challenging treatment and bolus cases with AlignRT. There is a VMAT mastectomy DIBH patient with two isocenters with bolus on the chest wall. Bolus is not used at the CT. We setup the patient to FB and BH reference surfaces normally inside treatment room without bolus. Then, daily, at the time patient is in BH and inside 1mm/1° accuracy in the “good” BH- surface (DICOM/VRT), we press pause, set bolus (covered with the paper) onto patient skin, quickly switch to an other AlignRT “bolus+treatment BH” field and acquire new reference surface for the treatment there and let the patient breath again. Then we ask the patient to take a breath to that same BH surface that we just acquired and once the values are again ok, we press pause, apply manually the planned shift laterally (18 cm or whatever it is in the plan), choose the other isocenter on AlignRT monitor, choose the “bolus+treatment BH field”, acquire new reference surface there and let the patient breath again. Then we do manually that LAT- shift back to first isocenter (to the couch LAT value that we had at the time we acquired BH- reference surface in first isocenter) and acquire first isocenter images there. (If there is a need for the couch shifts based on IGRT, we can do that and acquire new reference surface for treatment. After those possible small shifts we have to again ask the patient to take BH to that new BH surface and manually do planned LAT shift inside treatment room once patient is in BH and again acquire new reference surface to another isocenter.) Othervice we can use that same BH- field to the other isocenter, which has created before images, (still with calculated – planned couch shifts in LAT) which usually is the case. Then the imaging is performed to second isocenter (usually only tangential image to second isocenter). Then the first isocenter is treted and after that LAT shift to other isocentrer is again based on plan and it goes well to existing BH reference surface. Surprisingly well patients can hold their position in BH while we do not monitor them in BH during 1) bolus setup and during  2) couch shifts between isocenters in the setup. Also surprisingly often the errors in the images (if there is one) are systematical with this workflow, so corrections to setup FB/BH reference surfaces (without bolus) seems effective. Not any easy workflow for user to learn anyway, but on the other hand we have not had any flickering deltas with this and intrafractional control is better than with (for this kind of case easier) RPM.

BR Marko