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Discuss cardiac sparing for left breast patients with SGRT.
By jose_carlos_pichardo
I am having difficulty deciding what to do with couch vertical shift calculated from kV imaging pairs and MV imaging pairs. If we apply the VRT shift we are changing the breath hold level from that in our DICOM BH reference surface, so there is no way to be sure the patient is then holding the correct BH. Should we ignore the VRT shift is smaller than 1 mm, 1.5 mm, 2.0 mm? I assume that if the shift is larger than 2 mm this indicates that something is wrong with the setup and/or the patient's BH level. Does anyone have any insights? Thank you.
By jose_carlos_pichardo
Maybe a better question to ask is, how does one know if the VRT shift indicated by the kV orthogonals is due to an actual patient misalignment, an incorrect or inconsistent BH during imaging, or both? If we always apply the shift, we could end up in a situation in which the BH will be more than 3 mm off compared to the planned BH, and this is a problem for monoisocentric setup because of the matchline between the tangents and the supraclavicular field.

By marko_laaksomaa Finland flag

VisionRT has advised us to perform isocenter couch shift in DIBH such, that patient takes a BH to the reference surface used in the imaging, apply the couch shifts based on online match, acquire a new reference surface for the treatment and let patient breath again. In that way breath hold level  should remain the same after the couch shifts. Still it is not known what happens in the chest wall/BH while the couch is moving and does the patient take the BH exactly to the same delta value as she did in the imaging. Therefore I would always verify the succeeding of the action with tangential image before treatment and to be honest on the other hand therefore I would not much care about 1-2 mm couch shifts that you mentioned in practice. In the first fractions, when we want to achieve optimal reference surfaces for the setup and eliminate the systematic errors, I would finetune the setup surfaces with that kind of accuracy as you described. Then I would continue with daily tangential images and weekly with n+, mastectomy DIBHs verify that the vertebra and sternum remain inside 3mm in the orthogonal images in vertical direction, if so, continue four next fractions with the tangential images again. If there is a need to do the couch corrections based on orthogonal images in the weekly check, I can describe some examples in the different online match situations, concentrating on vertical directions only. In LAT image, in vertical direction...:

1. both vertebra and sternum have >3mm displacement in same direction, nearly as much, in comparison to DRR = only isocenter error-> couch shift described in the beginning of the text

2.  error mostly in the sternum is > 3 mm->  ask patient to take a BH delta outside of the zero value as much as the error in the sternum in the image was and acquire a new reference surface. Not necessarily need for the couch shifts, if the vertebra accuracy was good.

3. there is >3 mm displacement mostly in the vertebra, couch shift to vertebra. Not necessarily need for the new reference surface if the chest wall accuracy in the images was good.

In the point 2 and 3, you may need to take account the effect of changed LNG chest wall motion, since we changed the BHL and new orthogonal images may be needed. With the optimized workflow there is not often need for such rather repugnant online corrections 1-3, which is at least my goal with AlignRT DIBH, since using the IGRT for mostly verification only with certain action levels seems easier for the patient and the rtt.


By ellen_herron_bsrtt

Good question! We double check ourselves to ensure patient is taking correct breath by checking 1) heart contour on tangential film- this film in general could help confirm consistency in patient's breath since it is obtained after shifts and newly captured reference fields 2) difference in FB AP ssd and BH AP ssd and see how they compare to the planned  3) match to spine on lateral and if sternum is off, often times they need to take more or less of a breath to correct it
By marko_laaksomaa Finland flag
Hi Jose

Purpose of this text is to raise the discussion in the hospitals and share thoughts.

Some additions to my former text, now how to handle systematic errors concerning vertical shifts from orthogonal images, if we do not want to do those tricks 1-3 daily. In the point 1, where we have systematic isocenter error in both sternum and vertebra, and there has been a need to apply couch shifts patient in BH: we need new FB and BH reference surfaces and new couch vertical value for the upcoming setups (if the user uses additionally the planned couch vertical value for the setup). In point 2 where we ask patient to take more or less air into lungs based on mostly due to only sternum displacement in vertical direction, we need new BH surface and not necessary new FB surface. Still, I would always acquire new FB surface when we have to acquire new BH surface. Otherwise, there is a risk that there is something different between the FB and BH surfaces taken at different days, and we need to setup the patient also in BH in the upcoming fractions (do corrections on patient position or posture based on AlignRT BH surface after FB setup). This is what we would like to eliminate as often as possible. In the point 3 where we shift the couch due to mostly vertebra vertical error only, we need to acquire new couch vertical value (if the user uses the planned couch vertical for the setup as well) and certainly new FB surface. Still, I would always acquire also new BH surface when we have to acquire new FB surface. Otherwise…see text above.

To say it (too) shortly concerning BHL, in AlignRT DIBH cases errors in the sternum vertical we correct with the new surface with asking patient to take more or less air into lungs and errors in the spine vertical we correct with the couch shifts.

In the first fraction with AlignRT DIBH we begin the image evaluation accordingly: we acquire only LAT image and no matter what we shift the couch in the online match to meet the vertebra in vertical and LNG directions in the images. Then we ask patient to take BH to the window/level she sees on the monitor (DICOM surface) and acquire second LAT image. Now the vertebra is in its correct location in the image and we begin to check the sternum location. If it is too dorsally, we ask patient to take more air into lungs as much as the sternum vertical error in the image is. For this, we would like to have adaptive threshold feature, at least to only have a possibility to acquire new BH surface for the treatment with that feature. After we are satisfied and possibly acquired that new reference BH surface, we go on to the AP+LAT images. Once the images are “perfect”, patient chest wall is relaxed back to setup posture, possible couch shifts are taken into account, we acquire new FB gated setup surface (where we see entire arm tomorrowJ) and if we did not stick with the DICOM, we acquire new BH surface. We do not have FB DICOM from CT, and BH DICOM we take with the RPM guidance at the CT. We tested this FB+BH DICOM combination, but that often we finally found ourselves using VRT surfaces at some point of treatment that we considered it easier to create the FB VRT surface on the linac, at least so far.

In the first fraction, there are situations where we first shift the couch based on vertebra match in the LAT image and still based on AP+LAT images shift the couch out of that location again in LNG direction to make compromise match between sternum and the ribs. This is because rather often there is small displacement errors in between the vertebra and sternum in LNG and we cannot do anything for this patient pitched posture, except decisions in the matching location. Additionally, vertebra alone is typically the weakest possible location to finally match LNG direction, concerning the accuracy in the tangential image ribs LNG with DIBH. Therefore, if I think about the workflow where we would daily begin with the LAT image and vertebra match and see where the sternum is after that, I do not feel it practical, even if it may slightly improve the realized BHL accuracy. One reason is that there is a risk that we may begin, due to 1-3 mm shifts in the AP+LAT images, begin to daily acquire more images, acquire new surfaces for the treatment and go to record mode to get former surfaces active… The main reason is that nowadays with the AlignRT setup, the errors between vertebra and sternum are usually small enough in vertical direction in DIBH (in our latest data only 7% more than 4 mm). In another hospital with different workflow, with AlignRT, results can be of course different.

If in the weekly LAT- images users action limit allows less than 3 mm displacement in both vertebra and sternum location in vertical direction, this includes one risk. If in the images, the vertebra locates in the image acquisition position 2.9 mm too ventrally and sternum 2.9 mm too dorsally, BHL in the images is 5.8 mm too shallow, which error we should correct. How? Lower the couch 3 mm based on vertebra match and ask patient to take 3 mm more air than in the previous reference surface…

You had one question, where you wondered is the reason for BHL displacement in the LAT DIBH images due to wrong posture in the patient chest wall in FB or some kind of errors in (the workflow with) the system, which guides the patient to slightly wrong BHL. Based on the offline evaluation it is difficult to know, is the original reason for displacement errors between vertebra and sternum in LAT image that patient chest wall is more relaxed (too dorsally) or more tensed (too ventrally) at the CT in FB than it is in FB setup at the linac, leading to systematic errors in the realized BHL. We see these kind of systematic errors in the images also in the group of the FB breast patients sometimes. Or, is the reason something else in the workflow concerning the BH itself. If with the individual corrective actions you can get your LAT image repeatedly to match (both vertebra and sternum to their correct locations), this is most important. On the other hand, I feel that with the AlignRT you get much more supporting information how to correct setup errors based on offline images, if we compare it with the conventional tattoo setup. Needs to correct BHL after first fractions are rare in our case, but we need to know what to do once those appear. I think we will always face also these systematic BHL errors in the images occasionally and therefore there will always be needs to readjust the reference surfaces or planned couch vertical values at some point of treatment, typically during the first fractions, regardless how good our entire workflow is.

As noticed here on the forum, there are differences between the units on how to evaluate the succeeding of the BHL as a goal to spare the heart. One checks the diaphragm level and heart location in CBCT images, other checks the heart location in tangential images, third checks the displacement between vertebra and sternum in the LAT images, forth mostly relies on the setup workflow and the AlignRTsystem only…I have tried to demonstrate something about one way to do it.

Have a nice week-end
By jose_carlos_pichardo
Marko, thank you for your explanations. They were very helpful.

So my next question has to do with the final verification with the MV tangent portals. Should we shift based on these? My instinct says no, since these images do not provide orthogonal information. So what is the purpose for the MV portals? (1) To verify the relative position of the breast (target) relative to the MLC aperture and (2) to verify the position of the heart relative to the MLC aperture.  If these images indicate shifts >= 3 mm, what is your process? In your experience how often does this happen?
By marko_laaksomaa Finland flag
Good evening Jose

Tangential image is the most important image in the breast RT. With that we verify the tangential fields accuracy, typically most importantly CLD (central lung distance) accuracy. We evaluate it with matching the image based on ribs. Our AL for the ribs is 4 mm in LAT/VRT and 5 mm in LNG. The purpose of this bony match is to check that lung is not radiated more than planned. On the other hand, about the BHL, image is not telling much if the vertebra is not visible. The other important thing is to check breast tissue residual error. It should locate with our AL inside 7 mm (VMAT) and 1.0-1.5 cm + always inside treatment field (FiF..). With orthogonal images we do not see breast reliably. With AlignRT we have found it practical in the setup to verify/setup the soft tissue before images, after the setup is done with the ROI on the rigid chest wall. In the tangential images heart border may be visible reliably or not,  because sometimes it is difficult to say about the shadow in the image; is it rib or heart. We have 5 mm AL for the heart border in tangential image. These are the action limits we have with the tangential images for all of our breast patients. In the tangential images with RPM and with tattoo setup we only want to see the ribs, breast and heart, since AP+LAT images are taken daily because of large isocenter variation and thereby all the other bony areas of interest are visualized well in those images.

As mentioned earlier, with AlignRT  DIBH we mostly nowadays acquire only daily kV-tangential images with large field size, since isocenter variation is that small that couch shifts in the online match are inside tolerances and we rely on our workflow with the AlignRT. In the images we have vertebra, shoulder joint, ribs, heart and most of the breast visible in those images. Additionally to former ALs: vertebra VRT 4mm, LNG 5 mm, shoulder joint 7 mm in n+. To give you one single result of our data from the direction we are discussing right now and about the case you ask of: in 3% of the fractions 3 mm was exceeded in the tangential image ribs in vertical direction after othogonal images and after possible couch shifts based on online match.

Then the question would I shift the couch based on tangential images. If we treat opposing tangential fields in FB whole breast (WB), yes: both LAT/VRT and LNG. We have never shifted AP/LAT direction in practice in that group, but that is the only group where we would have justification to do it. I do not recommend to do it anyway. If we treat opposing tangential fields in BH WB, I would shift only LNG based on those images. If we treat opposing tangential fields in FB/BH and additional fields for lymph nodes I would shift only LNG based on those images IF, note if I see also vertebra and shoulder joint in kV- images and those are inside tolerances given above after shift. The reason for these are that based on tangential image we do not know how much there is real isocenter error in VRT and LAT. There can be 5 mm error in the vertical isocenter and 5 mm error in the LAT isocenter (in the orthogonal images) and those compensates each others such that there is zero error in the tangential image ribs. So if we mostly correct vertical isocenter based on tangential images and error really is in LAT isocenter it is dangerous, when treatment is given from any other angle than those two opposing tangential fields. This can be harmful for the lymph node area for example, if in addition to LAT error on the background vertebra is rotated such that th1 and thereby medulla rotates towards lymph node treatment field, all poorly visualized in the tangential images. In DIBH opposing tangential field cases I think that if we have displacement in VRT/LAT direction, we can not be sure is the reason for error in isocenter or BHL and that is why I would not ever shift the couch in LAT/VRT in DIBH based on tangential images.

With AlignRT as you noticed we rarely shift the couch based on tangential images only in LNG. We usually acquire new BH surface for that day treatment, only to avoid struggling with the deltas, but do not use that surface on the next day setup. On the next day we instead acquire AP+LAT images with the daily used surface which we activated back to use in the record mode and may be based on those images acquire new reference surface for the upcoming setups, if it agrees with the yesterdays couch shifts and everything else is still ok in the images. I think, it is not reliable to use reference surface which was created based on tangential image.

Best regards Marko
By jose_carlos_pichardo
When would you perform a LNG shift based on MV tangent images? When the ribs mismatch is/are what value(s)? What action is performed when the AL of 5 mm is exceeded?

Thank you.
By marko_laaksomaa Finland flag
...the purpose of the bony match to ribs in the tangential image is addition to verify the named radiated lung and heart area accuracy of course for its part to verify the target accuracy itself...

With MV tangetials I would shift only LNG direction and only in the group of n0 patients  treated with opposing tangential fields. In the MV tangential images I would use planned field size and thereby only ribs are visible. To open MV tangential field and daily acquire such images increases heart dose, and that is what I would not do. With the n+ patients I would not perform the couch shifts at all if there is needs for couch shifts in tangential MV image ribs in LNG, because lymph node area is not visible. When you have more than 5 mm error in the ribs in that group and you use MV tangential images, I think you need to acquire AP+LAT images before treatment and verify that the named LNG shift is adequate in the lymph node area also.

In the n0 group with opposing tangential fields I would shift the couch based on tangential image online match in LNG if the residual error in that direction is between 5mm-1cm and there is only 0-3 mm error in the ribs in AP/LAT directions. If the error in the ribs is larger than 1 cm in LNG or larger than 3 mm in LAT/VRT, I would acquire AP+LAT images and do the couch shifts based on those images before treatment. If the 5mm- 1cm error in the ribs exists mostly in LNG and AP/LAT error is less than 3 mm in the tangential images in n0 group,  I choose only LNG active for the couch shifts and do not choose vertical or lateral value active for applying the couch shifts or leave them zero in the online match when couch is not moving in those directions. So ask patient to BH to the surface used in the imaging, which led to 5mm-1cm LNG error in the tangential image, apply only LNG couch shift, acquire new surface for the treatment and let patient breathe again. Acquire new tangential MV image with the new surface to see is the image ok now. I would certainly not use that BH surface tomorrow. I would go to record mode to approve former BH surface active and start with that and AP+LAT images on the next day. This kind of possibility to have to shift the couch because the tangetial image ribs are outside of the 5 mm AL in LNG is possible in 7% of the fractions in our latest n0 data without preceding orthogonal images and couch shifts, with AlignRT setup only. Not often thus.

Best regards Marko

By marko_laaksomaa Finland flag
Forgot to mention one tip if you want to to use this combination of AP+LAT+MV tangential image. You find out that after your possible couch shifts based on AP+LAT image online match, tangential image ribs are not inside your tolerances, for example in VRT/LAT direction. Then you need to write down what is the problem with the tangential image isocenter, go back to match the existing AP+LAT images again to (re)do the couch shifts based on match to the slightly “better” bony structures, which better correlate with the tangential image accuracy and acquire reference surface for the treatment.Then you do not have to re-acquire AP+LAT images or accept tangential image with only moderate accuracy. Then acquire  tangential image once more with the just acquired reference surface. This is what sometimes happens during the first fractions if there is for example pitch in the sternum and thereby uncertainties to select the correct matching location in vertical.