Elekta AB (publ) (EKTAB) Earnings Call Transcript & Summary

Hello, everyone. Welcome to this Elekta webinar titled, Innovative Posterior Fossa trajectories with Leksell Vantage Stereotactic System. Our speaker today is Dr. Marie Krüger. Dr. Krüger, is a functional neurosurgeon at the National Hospital for Neurology and Neurosurgery at Queen Square in London. After completing her neurosurgical training in Freiburg, Germany, she did a fellowship in stereotactic and functional neurosurgery in Vancouver, Canada. Before joining the team at Queen Square, she worked as the Head of the Stereotactic and Functional program in Saigaland, Switzerland. Her main interests include DBS for movement disorders and pain, image phase, programming and planning, stereotactic lesions and MR-guided focused ultrasound, with extensive experience using the Leksell Vantage frame for biopsies, radiofrequency ablation, DBS and laser interstitial thermal therapy. Recently, her paper on her approach to posterior trajectories with Leksell Vantage Stereotactic System was published, which she will talk about live today in this webinar. My name is Dr. Helena Sandström, and I'm the Clinical Marketing Manager at Elekta in Stockholm. Before we get started, I would like to go over a few items so you know how to participate in today's event. You may have joined the presentation listening -- using your computer speaker system by default. [Operator Instructions] Please note that the session is being recorded, and the recording will be available on demand afterwards and shared with attendees and registrants. Thank you for attending. And without further ado, I will hand over to Dr. Krüger.

Okay. Thank you very much, Helena. Thank you, everyone, for joining. Thanks for having me and for having me invited to give this webinar. When I did the first posterior fossa approach a few years back, I didn't think I would give a webinar on this topic. But here I am, and thanks for joining. So I would like to share my experience with using the new Leksell Vantage frame to perform posterior fossa approaches because it's a little bit different from using the G frame that most of you are probably more familiar with. So let me just quickly make sure I have everything ready here. Okay. So just quickly my disclosures. This is the agenda for the next hour. So I would like to start with asking you, the panelists, 3 questions, just for me to get a better idea on your experience with the Vantage frame. And then I'll talk about the advantages and the limitations of the frame. And then I would like to show you 2 approaches or 2 different ways on how you can tailor the frame placement using landmarks only and also using the frame simulation, which is basically the paper that Helena just mentioned. I'm going to give you a few case examples and a quick summary, and then we'll probably have about 10, 15 minutes for questions. Okay. So we would like to start with the questions. And you will have something popping up on your screen in a few seconds. So my first question for you is, which of the following frame systems are you mostly using? And you can just type the answer using ABCD and E and if you're choosing E for other, please just write it in the chat so that we can see your answer there. And we'll show the result in about 20 seconds or so. So I started with the G frame in Freiburg, and then I used the CRW frame in Vancouver. And when our G frame broke in St. Gallen, we didn't want to repair it, but we got a Vantage frame. So I had to use the frame for everything. And I have probably never grown so attached to the G frame. So the switch wasn't too difficult for me. But let's see what your experience is. Okay. So most of you are using the G frame, quite a few the Vantage and some have other frames, which I can't really see in the chat right now. But most of you have the G frame or the Vantage frame. Okay, great. So we'll move on to question number two, what planning software are you mostly using? Is it A, the Brainlab software or B, the Medtronic Stealth? Or any other software or no software at all? I use Stealth and I'm now using Brainlab Elements most of the time. And these are probably the most common ones. We'll display the answers in a few seconds. That's very mix, okay. So Brainlab Elements 21%; and then Medtronic about 21%. 33% are using different ones or 20% none. Okay. So I can't see anything in the chat. Let me just see. So if you chose other, it would be nice if you could type in the type of frame you're using. But you don't have to, of course. Okay. So let's move on to the next question. Have you ever performed a posterior fossa approach with the Vantage frame? So first, Option A, no; and B, yes, but it didn't work; or C, yes, and it worked. So back to you. So no, okay. Good. That's a very clear answer. Good to know. Then you're all on the same page here. Perfect. Okay. So now I got a better idea of my audience basically. And I'll just go over here. Okay. So let me start by just talking a little bit about the advantages and the limitations of the Leksell Vantage frame. So most of you are using the G frame, so you're familiar with it. And you know that you were able to adjust the length of the poles and the height of the poles. And that's one of the biggest changes when you compare it to the new Vantage frame where you have this -- well, the whole frame is basically one thing, and you can't do these adjustments anymore. Another big change is that we have this upper ring basically in the front and in the back, which gives us a limitation at the upper part. And we have the attachment holder, the frame holder, which comes from the back and that also limits our window here in the back. The big advantage, I think, of the Vantage frame is the fact that it's very robust, and it has a very stable arc setup. So with the G frame I always thought that the X was a bit wobbly, that is definitely no longer the case with the Vantage. The X and the Y are sterile, which is very good, especially if you have to change coordinates during a procedure. And the ring coordinates are easy to read. You can actually read them on both sides now. There is this nice subscale, which allows you to easily plug in like sub-millimeter numbers. And our anesthetists have actually pushed us away from the G frame and always ask for the Vantage frame because they prefer it to the G frame because it has an easy access to the airway. It's a friendly design most, patients aren't that scared of it. And yes, it can -- you can't attach anything the wrong way. That is, I think, probably one of the biggest advantages. Once you got your coordinates, there is no way of putting out anything together in the wrong way. Now the biggest limitation, and I've mentioned that is that we have this attachment holder or the attachment ring and the attachment holder, which are reducing our window here in the end, at the back. And we also have this upper pole here. So we've got a biopsy window or an access window of 7x10 centimeters. And therefore, we have to usually tailor our -- the frame placement because we can no longer adjust our frame. So things like this that people did with the G frame, turning it upside down and then calculating the coordinates with some, well, formulas, that's no longer possible. I think that's a good thing because it's quite easy to make a mistake there. This is publication from Freiburg where they use the G frame and the RiechertMundinger frame. And this is something that you always have to do if you use any frame, really. If you have an access or if you're coming very far from lateral, you actually have to rotate your frame. And that is something that is still possible and necessary with the G frame. So that hasn't changed really. Now I've got a little video just demonstrating these restrictions again. So because of the frame holder, the arc system will bump into the attachment holder or the frame holder itself. And that gives you a limitation for your ring angle. And then, of course, you have the side pole and the upper arc of this pole, which gives you restrictions to decide and up there as well. So you are quite restricted in your entry area. There are 2 different ways of how to attach the arc: The lateral right, which is the one that you're most used to and the normal way of attaching the frame. But there's also a second one, and I actually wasn't aware of that when I bought or when we got the frame. You can actually flip your arc system around and use it as a lateral left approach to like this, and that will actually increase your ring angle. So you won't bump into the frame holder that quickly. However, you have to be careful if you're coming from the midline, you can actually bump into the attachment holder. So it's not as simple as that, but it can increase your ring because the ring -- the limitation of the ring is probably the biggest challenge. So I'm going to show you how you can tailor the frame placement using landmarks only. So without any fancy software or anything specific, this is on the publication because I'd like to use it because I think it clearly shows you the 2 things you have to think of. So when you want to place the Vantage frame, you really have to visualize your entry point and your target and the trajectory. And then the first thing that you should do is I would start with C and D. So you want to make sure that you're not bumping into the side poles. So like with every other frame, you're going to rotate your frame so that your entry point here is within your window. But then the second thing you have to keep in mind, because of the restriction of the ring, you can't just place the frame on and just making sure you have access to the posterior fossa. You also have to angle the frame so that your trajectory is not coming from up -- from down up, but from up down in relation to your frame. So as you can see here, this is your frame. And here is your trajectory. You're coming from lower up, and this is more than 180-degree angle, and that will block your arc. But if you put the frame on a little bit further tilted like this, you won't have to come from up down, but you can come relatively straight or even from up down -- sorry, you can't -- you won't come from down up, but from up down. And your angle will be less than 180 degrees. This will all become much clearer a little bit later. But these are the 2 things to think about. This trajectory, the angle and the rotation, so the draw and the pitch. You want to try to keep the frame as straight as possible, so don't make any adjustments to the role. Now if you look at a patient, it's good to kind of imagine or to know where the anatomical structures are that you're usually targeting. So we're usually targeting the cerebellum or the brainstem, the pons or everything below. We've got the sinus here. This is the ACPC line, and that is we like to transfer this line onto the skin for us, and we usually aim to place the frame parallel to this line. So it's very good to actually draw it because then that gives you a good feeling on how your normal frame placement would be and the adjustment you have to make. And then it's good to use the ear as a landmark because most of our targets will be around the ear area. You will have the ear canal as one landmark in the upper and lower part of the ear lobe and the posterior part of the ear lobe. So let's say we have a target just behind the ear lobe here and just above the ear canal. And let's say your software doesn't have this 3D model reconstruction. You can actually use normal MRI slides in the 3 dimensions. Look for your ear canal and then you know, okay, the entry point and my target will be just above it and just behind the ear lobe. And my entry point will be just slightly higher and then you can measure. On the axial slide, you can measure the distance from the midline to your entry point here. That's pretty much all you need, and then you can tailor the frame placement according to this. So here is an example. We have this target and this entry point. Just look at the blue line here. And we would like -- we mark the midline and then mark the ACPC line. And then the target in the entry and measure this distance here in the back and then draw the trajectory line to see how you have to place your frame. So I'm just showing you this in this little video. So I had a little phantom here. I have already drawn the ACPC line. I've marked the ear canal. And now I'm marking the target point, which is just right behind the ear and above the ear canal. And my entry point is just slightly below it. And I have measured the entry point from the midline and now I can connect these 2 points. And if -- you should really do that on the patient's skin. So now you can put the frame on and you can see your entry point and you can make sure that your frame -- the entry point is in the upper part of the frame that you've rotated it so that it don't collide with your site poles and also your angle. So this is just okay. They're almost parallel. You want your trajectory to come from up down and not from down up. So this wasn't perfect, but I'd like to use it to show you how precise you have to be if you want to do this. So now we have access, as you can see here. And now on attaching the Y and the Z coordinate. And usually, you have a sterile drape so you can attach them in the sterile field. And now we can place our arc system, and that's really nice because usually you just click it on and there's no wobbling around, but it just clicks on. And now you can lower it, and you can see that we can reach the angle. Now there are a few things you have to keep in mind. If your entry point was further anterior, you would sit on the attachment holder earlier. And if your ring had to be lower, you would bump into the attachment part as well with the guide holder. So this one was just perfect. But if I had to do it again, I would put the frame a little bit lower so that we have a little bit more leeway. When you get your stereotactic CT or MRI, I would recommend to get a stereotactic CT because the angles or the way the head is positioned in relation to the frame is a bit unusual and the patient's head is quite rotated and doing a 10-second CT scan is no problem. But having a patient in the MRI lying like that for a few minutes is very uncomfortable. So I would recommend just getting a CT. Sorry. That will give you your stereotactic ordinates. And then when you have your stereotactic ordinates, you want to make sure before you go into the OR, that your trajectory is actually feasible. So that's why we've got this table here. This table is also in the paper that Helena mentioned. And what it shows you is that if you have certain X, Y and Z., the ring limitations or the possible ring angles are like this and the arc angles are liking this. Now we have 2 lines here. The other line means that you can approach your guide holder all the way to the patient's skin. And the lower one is that you only want to come close, which can be good enough. But I would always aim to get the frame holder as close to the skin as possible. So this is very useful when you have your stereotactic ordinates you want to check that it's possible. And if it's not possible -- sorry, not used to speaking so much. So it's not possible, you can still adjust or make adjustments. We have the same order, lateral left approach. Same to the ring numbers, of course, are different here. And the same thing if you want to approach it all the way or if you just want to get close, but don't mind bumping into something. Here is the same thing using this virtual planning approach, which was basically what the paper was on. So when I started, I honestly didn't know whether it was possible to do this. So I thought theoretically, it has to be possible. But it would be nice to know what the frame or how to put the frame on the patient's head. So I thought maybe I can simulate the frame placement. And that turned out to be very helpful. I don't really think you need to do it like that. I think using just the landmarks and just looking at it is just as good. But it's good when you're starting and when you have a software that can actually do that. So now you're creating images on how to put the frame on so that you definitely have feasible coordinates and then you can take the images and try to put the frame on the patient's head exactly the way that you have simulated. So this is how that works. Now this is the Brainlab software, and this is the fusion tool. This should be possible with any other software really because every software has a fusion tool, where you're fusing in this case, the planning MR with the stereotactic CT. So this was just a phantom CT. And if you just use it normally, you can see that the trajectory actually bumps into the side pole and the frame is placed too high, and I don't have a good angle. So if you look at the coordinates, it's not surprising that with this X, Y and Z, these are not feasible. So you have a ring of 197. And actually, the highest possible ring is 179. So you already know this ain't going to work. It's not surprising. So you can actually go into your planning software and just adjust the frame placement or the fusion of the CT and accept it without it actually being properly fused. So what you can do is you can just rotate your CT to the site. You can place your frame higher and you can angle it so that now your trajectory is no longer coming from down up, but from up down. And here, you can see your X, Y and Z will change, of course. But if you look at your X, Y, and Z here, you're in this row, now your ring is actually feasible and your arc is feasible as well. So if you know that, you can create these 3D images, take them to the patient on the morning and put the frame on the way it's shown on images and then you get your actual stereotactic CT. And I've got a little video just showing the whole workflow. This is still from my time in Switzerland in St. Gallen, where I started this whole project. So this is actually the phantom CT that you can -- you have to do once. You just put a frame and a head box on a plaster skull and scan it. And then you have to create an object of the frame because the object will allow you to superimpose it on your 3D MRI scan. So you can use this tool and just draw it. And now you can see what it would look like if the frame was on exactly that way. So now here's our patient with planning and trajectory, just plan it the way you want to plan it. I will give you a few tips on how you can make it a bit easier for the frame and for you later on. But I would always, of course, plan the best trajectory that you would like to have. Now you can use your CT with your MR, the MR of your patient, and now you can make these adjustments. So it's very difficult to see here, but the trajectory is actually down here and here. So it would bump into the side pole, and it was way too low in reference to frame. So if I just accepted this and now I registered my CT, which is very quick and easy with the system, you get your stereotactic ordinance, of course. And the system will tell you it's not possible, neither with the lateral right nor the lateral left approach. So now you can make these adjustments. What if I rotated down and I rotated to the left so that now my trajectory is actually within the poles. And now you can see that looks much better. And if you compare it to the table, you can actually see it's better, but it's not perfect. So my ring is still too big. So I have to tilt it a little bit more. And I just made a very, very fine adjustment. I would actually make a bigger adjustment now. You don't just want to hit the most -- the possible number. You want to be comfortably in between the possible numbers. But now we have coordinates that are feasible. You can then use this, print it and try to mimic it or reproduce it on your patient's head. So that's what we're doing here. I used a lot of landmarks, the eye and where I put the pole in, really the easiest thing is to use the ear, drawing your entry, drawing your target, draw line and then just look at it and try to adjust it the way I showed you before. It's nice to have this extra visual confirmation. But I think it's even more important to just get a feel and an idea of what you can do and in the limitations. So now we just got the actual stereotactic CT of our patient. And we had this extra Vantage frame and just make sure that everything is working for the first few procedures. In the end, we didn't use it anymore. We checked with the table if the coordinates were fine, that's it. The surgery itself is super easy and straightforward then. We always put the patients in a half-sitting position. And it's, like I said before, once you got your coordinates, it's super easy. You attach everything. You can't attach anything the wrong way. And then that's it. You drill your hole, you can get your biopsy or do whatever you want to do. So that was the workflow. We did that for 10 -- in 10 patients. We had 5 brainstem lesions and 5 cerebella lesions, as you can see here. And this is what the virtual frame placement looked like. And here, you can already see. So all these trajectories have this angle slightly coming from up down in relation to your -- to the frame, except for this one. Here, I'm coming like this. So here, in this patient, we used a lateral left approach right from the start. And the same for this patient here, we also used the lateral left approach because you have more flexibility in your ring. So here, you can see the coordinates that we had virtually planned. And then these were the actual coordinates trying to fit the frame on as we are close to the virtual plan as possible, and this was the difference. So we found that the ring difference was actually only 4 degrees. The arc difference was about 6 degrees. And the X was only 3.3 millimeters, which isn't that much. The Y was 6 millimeters and the set on average was 11 millimeters. And the most -- the biggest difference was 2.3 centimeters. So basically, what I learned from these cases was that it was very difficult to put the frame on in the right level, and it likes to move up a little bit. So we had this patient here where the angle wasn't quite right, and we had quite a big difference in our coordinates. But that wasn't too much of a problem because we were just able to adjust the trajectory a little bit. And then we got -- instead of 178 degrees for the ring, where only 177 was possible, we managed to get it down to 176. So that's just a tiny adjustment. But it's good to know that before you go into the OR, because then you can check and make sure that it's still a good trajectory. And the other one was actually, like I said, this one here, what I said, was way too high. And now the Z was actually outside of our scanning field. And we had to replan everything. And with the Z coming up, the angle wasn't good anymore. And then the ring wasn't good anymore. But there was also no problem, we just switched to a left-sided approach. And with the left side of coin, it was actually all feasible. So the take-home message really is you can't adjust the frame. So you have to tailor the frame placement on the patient's head, and that has to be planned well and executed well. I remember it took me almost a whole weekend to do -- to plan the first one just because I didn't know what -- how it worked. And then the last few takes you a few minutes really. So you really get a -- quickly get a routine and using this virtual approach helps you to get a better idea of the limitation. So I would recommend it, but it's not necessary. A few other things that I could recommend is if you have a small head and sometimes it looks very weird the way the frame is placed, sometimes it's good to add another screw, to add a bit of stability. I'm not sure if it helped. It always helped me to be sure that it will be okay. We had this. This was the only complication we had. We had this screw, which went through the very thin bone of a 2-year old patient. And I think that would have happened with any frame because you have to make this -- do this rotation, if you have a trajectory that's coming through here. But the answer probably would have been to just use one of the more medial screws here. And that's another advantage of the Vantage frame that you actually have screws that you can -- or these holes where you can put the screws further in the middle and the G frame didn't have that. Other frames do, but this one, the G frame didn't. Okay. So I hope I was able to make that as clear as possible. So I'd just like to give you a few case examples now. So planning. Try to plan as straight and as medial as possible. I'm just going to give you an example. So this is a patient with a lesion. And there are very many ways to get to this lesion. If you have a choice, and sometimes you don't have it, but in most cases, you have a lot of choices, I would recommend to take an entry point, which is not that medial but quite medial and straight. So for example, this one is not medial. So we're coming in from lateral here and here is our target. So we're coming from very far out. And if you look at this, you can see the blue line. This is a much easier trajectory, both in terms of the axial rotation, but also in terms of this rotation here. Here, we're coming from low down and go up. And here, we're coming from up down. So if you want to put the frame on so that this becomes feasible with a right-sided approach, then it looks like this. So that's very, very rotated. It's not comfortable to do that. It feels weird. It works, but I wouldn't recommend doing that unless you have to. And if you have to have such extreme angles, it's actually better to plan for a left-sided approach. So this was actually the first patient I ever did. And I didn't really know that you could just flip the frame. So I thought I have to plan for this right-sided approach. And so I'd put the frame on with these weird angles. It all worked fine, and we perfectly hit the entry point here and we got a great biopsy and everything, and she was fine and so on. But I've learned from that example, it would have been much easier to just do a left-sided approach, and I'll come back to that a little later. Or to just plan a different trajectory. So instead of planning this extreme rotation and angle, just plan a single one coming from more medial, going slightly down. And then this here, if you do this, this is what it looks like and you can easily access or you can easily put the frame on and access the entry point. The next example is extreme angles, as I've just mentioned, try to avoid them, if possible. But of course, you can't always avoid them. If you have an extreme ring angle, plan for this lateral-left approach, like I just said. And if you have a very lateral angle, it's actually possible to plan to come from outside of the frame. So once again, this was this extreme angle. Here, you can see that I'm actually sitting on the frame holder. And I can't actually reach this trajectory with this approach. But if you just flip the frame, you can see you have more leeway in your ring and you can actually easily access it like this. If you have an extreme axial angle, sometimes it's better instead of making a huge rotation to the left. Like here for example, to just make a small rotation to the other side so that you can actually go pass the frame here. So that's also possible. This was one of our patients. I don't remember why I wanted to come from so lateral. But for some reason, I thought that would be the best way and then that's the way to do it. This is actually what the frame placement looked like. So it doesn't look too unusual. And then you can just come past or next to the frame basically and between the ring and the frame. So should you aim for lateral right or lateral left, I -- like I said, I would prefer a lateral-right approach whenever it's possible because you can use the lateral left as a default. Whereas usually, if you plan for a lateral left, your angles will be so different. You're correcting it or you're moving in the wrong direction, you can't use the right -- lateral right as a default. So I showed you this example earlier, and that happened a few times after. So it's good to plan for lateral right and have lateral left as a default. So here, for example, I, basically, the frame moved slightly too far up, and it wasn't tilted perfectly. So you can see my line here, I'm coming from down up and instead of this way, I'm going up like this. And I'm bumping into the frame holder. And you can easily just flip the frame and then you have access to this. So as soon as your ring angle is more than 180, roughly, then you can do this as a default. Another thing that you need to take into consideration is that the Y and the Z, they also matter. The Y, I'm just demonstrating this with the Y. The smaller the Y, the easier. Because in our system, the 000 of your X, Y, and Z is in the upper right back corner. So the bigger your Y, the further anterior your target. So for example, this Y is smaller than this Y. The further anterior your target is, the sooner you will bump into the frame holder. I just have a little video here demonstrating this. So I'm attaching the frame holder. Now you would put a drape on -- sorry, you'd put the drape on and then you could attach the Y and the Z in the sterile field. And you can see that I'm bumping into the frame -- the attachment of the frame holder here. And if I were, I would bump into the frame holder with the guide holder. So again, you could switch to a lateral-left approach. But this is not -- the point I'm trying to make here is actually that if -- I think I speeded up a bit, sorry. If your Y is smaller, like in this example, you can see how you can get lower down because you're not sitting on it that early. And the same applies for the Z. So the smaller the Z, the higher up your target and the more leeway you have before you bump into the attachment holder. And the bigger your Z, the lower down you are and then you're bumping into it earlier. So these are also some things that you just have to keep in mind, and it's just good to play around with the planning software a little bit and see how the coordinates change and how your field of access changes when you make these changes. Okay. So that was basically what I wanted to share with you. So as a summary, in terms of the planning, again, try to go straight and as medial as possible, avoid the extreme ring angles. But if you need to have a big ring, go for a lateral-left approach. If you have a very lateral approach, you can actually come from the side. I would always recommend to plan for a lateral-right approach as long as it's possible and then just use the lateral left as a default. But this is just my personal opinion. So it might be better to always aim for lateral left and then you don't have to worry about the ring too much. And then the smaller the Y, the easier. The smaller the Z, the easier. So just a few things to consider when you're planning and especially if you have a big lesion where you have a lot of possibilities and you don't have to just aim for one specific point. So again, to summarize, I personally really love the Vantage frame, especially DBS, but it's also a good frame for the biopsies. It's robust, it's stable, you got the sterile X and Y, the ring coordinates that are easy to read, subscale, easy access to the airway, a friendly design and you can't do anything wrong, if you've done your planning right. But it's less flexible, definitely. But the posterior fossa approaches are possible. You just have to be aware of the limitations. You basically have to know your frame and that applies to every frame. And I think moving from the G frame to the Vantage frame, for someone who has used it for a long time, is probably a difficult step to make. I never grew too attached to the G frame, so it was quite easy for me to make that move. But once you've got to know it, it's actually a brilliant frame, and I really like it. So thank you very much. And I would like to stop sharing my screen now, so that I can give everyone of you the opportunity to ask some questions. So let me just see how I do that.

Thank you, Dr. Krüger for a very interesting presentation. We will now take questions from the audience. [Operator Instructions] We have received a few questions. First question is, how do you fix the frame when you perform bilateral DBS to the dentate nuclei or cerebellar peduncles?

Could you repeat the question? I was distracted by the -- getting everything ready. Sorry.

Yes, of course. How do you fix the frame when you perform bilateral DBS, to the dentate nuclei or cerebellar peduncles?

DBS to the dentate nuclei. Okay. So we don't do DBS down there. I think that was a new thing. I've never done a DBS in that area. So my DBS, the lowest is probably the STN or the GPi, which is about 5 millimeters below the ACPC line, and then you would just come from anterior here. So I've never performed a posterior fossa DBS. I guess you would just have to -- you could just plan it. And just apply everything that I've just said. But I can't tell you out of the top of my head, you have to look for this or you have to make sure that this and this, to take this and this into consideration. So I'm sorry, I can't answer that specific question. But it's interesting to hear that people are doing that.

And we have more questions. Have you ever considered placing the patient on the side in order to be able to switch from lateral left to lateral right arc orientation in a simple manner?

So I never really considered switching to the site. What I often thought about was just placing the patient face down, but still using -- like still scanning the patient lying on the back and getting all the coordinates. But if you place the patient face down, you could get rid of the -- not the attachment rings, I got it here. Not of this ring, but of this one. And if you are getting rid of the attachment holder, that gives you a lot of -- a lot more freedom with the ring angle. So that's something I thought about, but I always managed to just adjust my plan so that I didn't have to do that. But in theory, that would probably be possible, and you could just make sure that the patient's head is nicely cushioned, like they do it for the spinal surgeries. Placing the patient on the side, I'm not sure that would give you such -- so much more of an advantage really because there will probably be a strange angle, but putting the patient up like face down would be an advantage because you could get rid of this part that blocks the ring. I hope that answers the question.

Thank you, Dr. Krüger. And next question is, have you used specific equipment for infants less than 2 years at all having brainstem tumors?

We know -- so I think the youngest we did was a few months. But we didn't use any specific equipment. You just have to be aware that when you screw in the screws, it's very soft and you shouldn't screw them in too deep. But I didn't use any different or special equipment. And I've done maybe 2 children under 2 years. So I don't have a huge experience with that. But I didn't -- no, I didn't use any special equipment or anything.

The next question is, how long does it take to do the preparation prior to head fixation?

So that depends very much on the level of experience. So like I mentioned during my talk, the first one took me a whole weekend because I just -- I went through all the possible things that could go wrong and I played around with the phantom and so on. But once you've done it a few times, the learning curve is very steep. I would say, it takes me 10, 15 minutes to plan a posterior fossa approach now because if you just know what to look for and it's not much more tricky than a normal biopsy really. It's actually sometimes easier because you kind of know what you have to look for and what you don't have to look for. Whereas, sometimes up here, you run into other problems. So yes, I would say after maybe 5, 6, it won't take you much longer than planning for a normal biopsy.