Latest Clinical Experience with DoseRT and Beam Guide

Dr. Florian Stieler (00:04):

I’m going to talk today about our latest clear nuclear experience with DoseRT of imaging and the new Beam Guide functionality. So my talk is split into the two topics. First of all, I would like to start with the Cherenkov of imaging, and I would like to give you some basic information. What is Cherenkov Imaging? So first of all, yes, it’s blue light. So some of you may know this old movie, which shown up there. So Cherenkov Radiation is an electromagnetic radiation with a wavelength above 300 nanometers. And I looked into my old physics book to find a nice definition for Cherenkov Imaging and why it is occurring and when. So if a charge particle, for example, an electron, moves in a medium faster than the speed of light in that medium, this Cherenkov radiation arises.

Dr. Florian Stieler (00:56):

So what does that mean for us in the clinic? So when we have a beam hitting the patient, the Cherenkov radiation arises right there where we irradiate, so at the entrance point and also at the exit point of the beam. So I think that this is also a very useful tool in the field of risk management, which is quite important in Germany as well. So that’s also something that we are currently working on. So, how do we see, how do we acquire this Cherenkov irradiation? So it’s embedded currently in the AlignRT software with DoseRT. So we have two additional cameras mounted in the treatment room. Ours were installed in March, 2024. Currently, we are using version 7.3, but we will update hopefully pretty soon to version eight then. And we also have a special phantom play to make the Cherenkov radiation visible.

Dr. Florian Stieler (01:54):

So what can you do with this? Actually Adi, Mike and I published just recently a review about Cherenkov Imaging in radiation therapy. So this is a, a very powerful and useful tool for the surveillance of the radiation therapy in real time as well. So that means we are looking for the localization of the radiation, like in the contralateral breast and so on. We are looking for the beam geometry, so that means beam direction, field sizes, and the intensity of the radiation can be analyzed. We could check the correct bolus position and also, for example, seroma monitoring after lumpectomy. These are some examples then from our clinic. So we looked in some breast cases with tangential irradiation and also VME irradiation with the internal lymph node in the PDV and in the upper lymph nodes so that we can see here some additional Cherenkov signal on the contralateral breast.

Dr. Florian Stieler (03:04):

But this was known during treatment planning, and it was accepted also by our physicians, but we also looked into some SBRT cases, head and neck cases, prostate cases, and one of our most complex cases, some cranial spinal irradiation that we analyzed also with Cherenkov. But I want to focus right now on some of the interesting use cases that we saw. One was the validation of the treatment planning. We did so we eradiated a young children with a single VMAT a single isocenter VMAT boost, sorry, in the neck and abdomen region with an interruption intersection here in the center where we wanted to reduce the dose to almost zero. The point is usually we are using the two separated rotations to treat that in order to get rid of the so-called do symmetric leaf gap that we may have using our electro linear accelerators.

Dr. Florian Stieler (04:08):

But in this situation, the children were under general anesthesia and that was also the reason why the arms were positioned downward as such. So it means it was necessary to treat everything in one rotation. So I was curious after irradiation, do we see some Cherenkov signal between the two PDVs? And when you look at Cherenkov image down here, you actually see very nicely this kind of low-dose area. So we don’t see any Cherenkov signal there. The other point was that we had a sarcoma irradiation in the right shoulder of a patient. So during treatment planning, we accepted the plan without any dose in the neck region and especially in the chin. But then when we looked at the first fraction of the treatment, so the summarized Cherenkov the image, we could see that some signal arrived in the neck region.

Dr. Florian Stieler (05:11):

And then I was curious, okay, where is this coming from? And when I looked at the, at the VMAT segments, I could see that the chin is sometimes very close to our MSC segment. And when the chin was positioned too far down on the patient, then this Cherenkov radiation arises. So that means I told the RTTs, okay, please, when you position a patient with cone beam CT and SGG also take care about the chin, try to lift the chin of the patient. And then on the next day, I looked at the Cherenkov images again, and I could see, okay, the Cherenkov is now much lower than on the day before. The next one was again a sarcoma in the left leg of the patient. So the patient was positioned with feet first.

Dr. Florian Stieler (05:57):

Here we actually used two 10 beams to each other, and I was a little bit surprised that I could see so much Cherenkov signal in the opposite leg. So I reviewed our cone beam CT, and I could see that the right leg actually was positioned closer to the left leg than it was planned. So again, I spoke to the RTTs, and I said, okay, please don’t focus only on the left leg. Also, look at the right leg to see if it’s far enough away from our PTV region. Then I reviewed the next day, the Cherenkov data again, and I could see, okay, much less Cherenkov signal in the other lag here. Also, this was positioned much better with our CCI was talking about risk management and also how to review the data.

Dr. Florian Stieler (06:52):

We have one indication that we are treating in our department, which is following the stop storm trial in the, in Europe. So that means we are treating a stereotactic. The, we are doing a star irradiation, which is a stereotactic arrhythmia radio ablation for ventricular tachycardia. So it’s actually no cancer. And actually it’s, it’s a very powerful tool. It works. I was quite impressed of the outcome of the patients. So the patients were actually treated before with all the other possibilities like medications, surgery, and so on, and nothing helped. So then we followed a stop stone trial and we irradiated the patient with a single session of 25 gray with a six triple F beam. We positioned the patient obviously with cone beam CT, SGRT, and then we also acquired the Cherenkov in signals just to make sure, okay, we are in the right spot afterwards.

Dr. Florian Stieler (07:53):

And as you can see, actually, it matched quite well to what was predicted by the treatment planning system. So that was actually also something that we stored in our medical record for the approval or for the improvement that actually we originated the right area. So, concluding the DoseRT part, so DoseRT provides real-time information about the dose deposition depending on the daily position and also on the LINAC delivery. So it takes the patient and the LINAC into account. We have a high confidence in the delivery of complex and high-dose treatment plans. With this tool, the RTTs can interrupt the treatment when they notice problems during the delivery and also the physicists and physicians can review the delivered treatment fractions afterwards to review the dose delivered to the patient. So then I come to my next part, which is our first clinical experience with Beam Guide.

Dr. Florian Stieler (08:56):

So we have the system for I would say two months, three months now, and we have done some testing with it. So what is it? Some basic information. So it’s a new functionality in the in real time information in the Postural Video feature of AlignRT. So it means we can now see the plant beam outline, which is the white line and the real-time beam projection, which is the yellow area. We can turn on this option in the Postural Video and also turn on either the projection or the outline. So that means it gives us a kind of predicted information about the treatment field and real-time information about the treatment field correlated to the actual position of the patient. So that means also that Beam Guide is giving us or is giving the RTTs information about the anatomical effects or the consequence of a patient misalignment either rigid or non-rigid. So that’s actually a new feature, and I think that’s quite important also for the RTTs to understand, okay, where are we are originating and what part of the body is important to be positioned in the right way.

Dr. Florian Stieler (10:15):

So I would like to present some of the examples that we had. So the first one, obviously, we looked at a tangential IMRT in this case, in free breathing, in the right breast. And here it was the case that on the right side, you can now see the patient in the correct position. So that means the yellow area corresponds to the white predicted area. But I ask them, the patient, okay, could you lower the right arm just to see what Beam Guide then does? And then you see, now we have this yellow area in the arm instead of in the breast. And also we see a kind of, yeah, low dose area in the region of the sternum, because now obviously the treatment plan changed because the anatomy of the patient changed. So then we started with the real treatment.

Dr. Florian Stieler (11:03):

So, before positioning this was a screenshot before the positioning. So as you can see here, we have a quite a large lateral deviation. This is actually necessary because otherwise our Elekta machine cannot do a cone beam CT because of collision issues. So we have to position the patient more or less in the centre, the isocenter in the centre of the patient. Therefore, we have this lateral deviation. And then, yeah, thank you for starting the video. That was actually the move meant back after the cone beam CT and you could see how the Beam Guide information changed during the movement of the couch after the cone beam CT. So this is all in real time. So that means the RTT can evaluate and see how Beam Guide then starts matching after the treatment. I also reviewed the DoseRT information. Actually this was taken the next day honestly because we have currently two software versions on, on our, on our workstation. So I have to reboot the computer currently to the other one. Anyway, when we compare the Beam Guide information with the DoseRT information taken the next day, so actually we saw quite good agreement of these two.

Dr. Florian Stieler (12:35):

Okay, next video. This was a second IMRT case for right-sided breast cancer. Again, you can see how Beam Guide starts matching when the patient is in right position. You can see also the Beam Guide information from the other, other two cameras. We have horizon cameras in our hospital, and actually you can see that the patient and Beam Guide matched quite well to the positioning of the patient. But then I was interested in the VM A D boost. We are treating the patients with a simultaneous integrated vm, a boost here. And obviously the Beam Guide information is now looks totally different. It looks like a belt around the patient and we could see that we have some role deviation here of two point seven degrees. And when I then looked at the Beam Guide information, I could see this slight deviation on the contralateral breast. So that’s actually what I mean by what is the effect of a mispositioning of the patient on the couch on the, let’s say, irradiation of the patient.

Dr. Florian Stieler (13:42):

Then we had another paradigm that we looked at prostate cancer treated with VMAT two rotations in our department. Patient was lying in prone position and here, as you can see, we see a, a small lateral deviation. This was actually the screenshot taken after cone beam ct. So that means we position with beam CT obviously to the internal position of the process. So that means with the SGRT system we saw a slight deviation and this slight deviation could also be seen with the Beam Guide information. So that’s actually pretty nicely, yeah, synchronised, but we could also see a slight roll deviation again, funnily again 2.6 degrees. And also this could have been seen when you look at the agreement of the yellow area to the prescription to the prediction of the wide area.

Dr. Florian Stieler (14:41):

So you see a slight deviation on the left side and also a slight deviation on the right side, but in the center actually it looked quite well. Also, in this case I analyse the DoseRT data, which actually looks more or less the same. So that’s actually also a quite nice tool. It would be nice to automatically compare everything. So that’s what I mean by we need some additional tools to actually then compare Beam Guide with DoseRT. That would be the next step for me. Then we treated some iliac bone on the right side with a partial VMAT arc. And here we could see that because we treated the abdominal region, the patient when while most treating while was treated, was obviously breathing. And what you could see then is how the Beam Guide actually comes, I think in the next video a little bit better how the, how the Beam Guide agrees to the wide outline depending on the breathing of the patient. So that was also quite interesting. And we also want to look into the, yeah, deep, deep inspiration breath treatments with Beam Guides and to see if we really see some advantages there to use Beam Guide for this.

Dr. Florian Stieler (16:00):

The last paradigm we looked at is a treatment of a thoracic wall following the fast forward trial. So it’s a hyperfractionated treatment with VMAT for this patient in breath hold. But the patient was treated in 20 with 26 grade in five fractions. The point is here in this situation, that’s why I took it. The Beam Guide showed actually a lot of information because it’s a large beam field over the whole body. So, here at some point, I would recommend that RTTs turn off Beam Guide. Just focus on the let’s say on the, on the, on the shift vector and just for verification, turn on the Beam Guide check, okay, does it match or not? But what was interesting is the, let’s say the Beam Guide information in the chin did not match.

Dr. Florian Stieler (16:53):

So, but we saw that during so before the treatment, so we asked, asked the RTTs, can we reposition the chin? And it was actually not possible. So the patient was very stiff on that day. So the patient, yeah, was not so compliant on that day. So it means okay, we have to accept it the way it is right now. Then what I did was after positioning, I rebooted my workstation, changed to the DoseRT and to actually record Cherenkov information. And what I could see is, yeah, I see some dose in the chin, which was actually not part of the original treatment. And then I reviewed Cherenkov data from the day before, and I could see, okay, on that day, the patient was positioned much better, the chin was higher. So that means that was a one-day situation in which we treated that patient.

Dr. Florian Stieler (17:50):

But actually again, the RTTs took care about that on the next days or on, yeah, the next two days actually. So they knew what to look at. Okay, concluding the Beam Guide and also part of the DoseRT topic. So, Beam Guide provides real-time position and monitoring information to the RTT. Deviations of the patient position in translation and rotation are recognised with Beam Guide, the RTTs, and that’s, I think, also quite a nice new feature in SGRT. The RTTs receive more information now on the treatment location and on the region of interest, which helps to position the patient. And the Beam Guide provides monitoring information also for conventional, but also for DIBH and gated treatments. So that means for me, my conclusion of the day is the combination of Beam Guide for treatment prediction and DoseRT for treatment verification. Increase our safety in radiation therapy. Thank you very much. And I’m open to questions.