This is Ganesh, medical physicist at Univ of Arkansas for Medical Sciences and I attended Dr Agazaryan's talk on Brainlab at the AAPM annual convention. I have a follow up question on the topic.   We have been using Brainlab MME ver 2.0 with Exactrac localization for little less than an year now. Our physicians define the tumor contours (GTV) for multiple mets on CT after fusing with MR. When it comes to defining the target (CTV or PTV) using a treatment margin, I would need an overall treatment error for a single-iso multi-mets plan and a single cranial tumor plan. We use single iso and multiple non-coplanar arcs in Truebeam sTx and planning is done on Brainlab MME ver 2.0. Our suggestion had been 0.5 mm margin for any target within 5 cm from txt Isocenter and 1 mm beyond that. I would like to double-check these margins with what is used at other institutions. ​It would be great if you can share your thoughts. We wont necessarily use it per se, but would like to have a good comparison point.

    • Dr. Nzhde Agazaryan - UCLA - Dear Ganesh, thank you for this interesting question.  Our research presented at AAPM suggest that 0.5mm margin for targets up to 6cm away and 1mm margins for targets further away is likely a good strategy (to be validated by clinical trials).  So your approach of using 0.5 mm margin for any target within 5cm and 1mm beyond that is reasonable. With all that said, originally we have been using larger margins, so we decreased our margins and started using 1mm margins for all targets uniformly.  This is based on a logistical issue with eth software and issue with developing a comfort level before going to a 0.5mm margin for closer targets. For single target single iso treatments we also use 1mm margin.  However, the Exactrac tolerance settings are different for these two scenarios. Please see the table below (click on the thumbnail).  I hope this information helps. brain
        • Thank you Dr Agazaryan. Appreciate it. Let me know if there is a publication on these treatment margin data.
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