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[brett_thomas]

Hey all, our center started using OSMS in July. There have been mixed feelings about it. One of our biggest problems is during DIBH Treatment after 1 or 2 of the fields we will get "maged" out we call it they are still in tolerance but their mag is just out. The other issue that we see is sometimes their breath seems to change and they fall out of tolerance. We try to coach them back in but sometimes it doesn't ever match back up. Any tips tricks or tolerances you would suggest?

Thanks, Brett

[floortjebrus]

Hello Brett,
It can take a bit of time to get used to using OSMS, but at our center we find it very efficient, accurate and helpful to setup and monitor/gate our DIBH patients. We set our DIBH tolerances to 3mm for the translations (lat, Long, vrt), and 3° for the rotations (rot, roll, pitch). We first set up our patients using the FB (free breathing) DICOM from the planning CT, and correct for the translations and rotations as close to 0 as possible. Then we switch to the DIBH DICOM from planning CT, and ask our patients to breathe in and hold their breath so that the vertical is within the 3mm tolerance. It is important that they can hold their breath within this range, as this has been calculated in planning. If patients are unable to consistently hold their breath within this range, they may not be suitable for DIBH. We practice this during the planning CT to ensure it is reproducable during treatment. The amount they breathe in is calculated in planning, so when we set up the patients in FB first, they should be able to breathe in and hold their breath within the set vertical DIBH DICOM. Once they breathe in correctly, we may make minor adjustments to the table for the long and lat if necessary, but certainly not the vertical. We leave the room once we are pleased with the setup, do daily portal MV imaging on DIBH, and confirm the chestwall/bony anatomy and breast contour. Any small shifts after matching get made while having the patient breathe in, and we take a new reference at that moment which we then use to monitor and gate our patients for their treatment that day. We rarely have any issues this way during the DIBH
treatment. We find it is important to properly coach the patients during the planning CT on how to consistently breathe in and hold their breath. i.e. they should not breathe in lifting their entire chest or body, because then they may actually move themselves out of tolerance.
Another reason why the mag could go out of tolerance is sometimes with IMRT DIBH breast plans, it is possible that the gantry can block some of the OSMS pods/cameras. It helps to have an ROI that covers the treated breast, but also extends a bit beyond the midline, and wrapped underneath the non-treated breast. This way the pods have a slightly larger area to observe without going out of tolerance. If you are uncertain whether the patient actually moved after a few treated fields, or whether the mag is out of tolerance due to camera blocking, you could drive the gantry to 180° or 0°, have the patient breathe in, and check the OSMS values again. If it is within tolerance then, it is most likely due to camera blocking. Try adjusting your ROI. In some difficult cases, we may take a new image to confirm the anatomy and shift if necessary.
I hope this helps! Feel free to ask for anything else. Success! Greetings, Floortje

[ellen_herron_bsrtt]

Hey Brett,

We set up the same way as Floortje. Works really well going to FB first then to the DIBH reference. We have learned to tighten our rotations (rot, roll and pitch) to a 2 degree tolerance. The tighter these bottom rotations are then the better your patient will setup and less room for variance. We get the rot, roll and pitch as close to zero as we possible can on FB reference setup. Then usually when switching to DIBH they fall right into tolerance. If a minimal lng or lat shift is needed then we do make that shift. Like Floortje said vrt should only be manipulated on DIBH scan by coaching patients breath not moving table.

We've also learned during films to look at your spine and sternum (along with breast). If there is a difference from original DRR then you may need to coach them to take more or less of a breath.

Then lastly, check to make sure you have a good ROI drawn. If ROI is not sufficient then parameters on AlignRT computer may flicker, which can make if very difficult to treat a DIBH patient. If you need any examples, then let me know!

Hope this helps!

[brett_thomas]

Do you always set up to DICOM or if you have moves from your port films do you set up to VRT the next day?

[marko_laaksomaa]

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?

[daniel_vetterli]

Hi Brett
I guess Floortje described the setup process in perfect way and also addressed some of the technical pitfalls like shadowing effects.
Concerning your problem with MAG tolerance. It also might depend on teh software version you are currently using. In version 1748 you have for vrt, lng, lat and MAG only one comon tolerance which is somewhat unfortunate. If vrt, lng, lat happen to be all close to the tolerance, e.g. 3mm, then MAG will be out of the 3mm tolereance. Because of this shortcoming, we do not use automatic beam gating. However, with version 1749 you can choose individual tolerance levels for all coordinates, as well as for MAG. So in this situation you can choose a larger tolerance for MAG which might solve your "maged" out problem.
Other than that, you will probably always be confronted with "difficult" patients which cannot keep their breath level despite good coaching. That's reality in clinics! I think it is important that you check your (BH-)setup with imaging and make sure that the thoracic wall is lined up well with your reference DRR. The goal is for sure to reach the correct vrt level (via correct amout of air intake) without adjusting the couch vrt after setup in FB, but in case the patient does not manage to reach the correct level it might be apropriate to rise the couch a bit such that the thoracic wall is lined up again with your reference DRR. Like this you make your that the ptv is within your treatment field. The drawback might be a bit more dose to the heart but it will still be better than treating in FB.
Maybe this helps a bit, Daniel

[marko_laaksomaa]

That is an easy way to think the breast treatment workflow if it is enough that tangential image chest wall and breast is in good order.  We do not want to raise the couch vertical inside treatment room based on how well patient reaches the RTD VRT level without verifying the realized breath hold level from LAT- kV images and the workflow becomes much more complicated, naturally.

[daniel_vetterli]

Hi Marko,
yes, my suggestion is easy, but sometimes with difficult patients I guess one has to choose pragmatic and feasable solutions. When you face difficulties and you start imaging and rotating gantry back and forth, I am not sure at the end of the day if you are more precise. I am for sure not advocating for a sloppy treatment practice, and I fully agree that DICOM_BH is and has to be the gold standard, but if we like it or not, sometimes patients have a bad day and cannot cope with what you want them to do. In these (rare) situations I guess it is justified to treat, if PTV is at the proper location, even when the lung volume is not exactly what it should be. There was even a time before DIBH....

[marko_laaksomaa]

Hi Daniel

Nice talking with you. I understand and agree your point completely in the problematic cases as you mentioned and may be at one fraction or so. Substantial variation in the heart position is reported in the DIBH (Heart position variability during voluntary moderate deep inspiration breath-hold radiotherapy for breast cancer determined by repeated CBCT scans, 2017) and partial DIBH is better than FB (How important is a reproducible breath hold for deep inspiration breath hold? 2015). In commonly to this forum: does these knowledges give us a permission not to take care of correct BHL? There are studies where statistically significant heart dose changes is noticed if BHL remains systematically partial (Cardiac dosimetric evaluation of deep inspiration breat-hold level variances using computed tomography scans from deformable image registration displacement vectors, 2015). These systematic changes in BHL is what we want to pay attention to. I do not know many hospitals that are systematically verifying the BHL at the beginning of the treatment (with measuring the errors of the distances between vertebra and sternum in VRT and LNG) from the LAT- kV images and Ellen mentioned that they do, and I was excited and pleased.

Based on RTTs daily work with SGRT, I am not for sure that is it in all the problematic situations the patient which can not cope with what we want them to do in DIBH. I think there is still something for us users to learn about how patient should repeat DIBH daily similarly with the SGRT-quided, and not at all the situations trust blindly to the workflow we have created with operating with RTDs, ROIs etc.

I would also like to go towards easy and commonly used IGRT protocol in DIBH where we acquire mostly tangential images only (which are indeed in good accuracy already) or even weekly IGRT at some point, but  I think it is not possible before we are completely sure and can trust that based on SGRT- setup all the bony structures, and thereby OARs, inside or near PTV are systematically inside margins used for whole PTV, in the individual- and population basis. Is one workflow with SGRT better than the other, we do not know yet, but the goal with this system is the systematic reproducibility of the bony structures, breast and isocenter in the setup images (CBCT, orthogonal and tangential) during the whole treatment session, hopefully with as small effort as possible. It needs offline investigation of the images at the beginning of the treatment of individual patient and finally investigation of the accuracy in larger population to estimate that is there something to improve in the system or workflow.