Transcript
Okay, yeah. I'm happy that everyone made it here this morning after the nice, excellent social event. So thanks for coming. This is where all the cool stuff happens, right, the physics session. So here's my little disclosure. So what I would like to talk about in the next couple of minutes is, more or less, a kind of complex multifocal planning. And then we have a glimpse, look at IGRS requirements because that's quite important when talking about things like that, using virtual isocenter and so on.
First of all, we have to reconsider or have to consider, what would we call a complex planning situation? And I just wrote down three points that came into my mind. And the first one was, okay, maybe when they have a large number of lesions, clustered or not. We heard a lot about that yesterday already. The second point would be maybe if we got different prescription regimes, so we got maybe a large lesion, but we want to give fractionated SRS or SRT. And maybe we have got some SRS as well, some single shot, or we want to go to the high dose in one session, so that might make the situation a little bit complex. And the third thing that came into my mind was maybe if we got different indications. So we got maybe multiple lesions, just multiple brain metastases, and one was the surgery maybe because it was quite large. And then the neurosurgeon has decided, "Okay, we'll take that out." And then we have to irradiate the cavity as well.
So then I thought, okay, let's talk about that. And then I picked just one case out of our clinic, and I thought, "Okay, why not put it all together in one case?" And this is a typical case we have. So this is the 50-year-old male patient, got lump cell, first diagnosed, six brain metastases in July last year. And so here's just an overview of the software, that we have an idea where they were positioned. And one was a very large one, so they got rejected by our neurosurgeons in the hospital. And the patient came to us and they said, "Okay, let's do something about that. You have to irradiate that. We want to be sure that everything is okay." And we said, "Yeah, sure we can make it."
And then we looked at the images and thought, okay, this might be the fractionated thing because if the cavity is still normal, we get 7 times 5 gray to that, like an ICRU conformable medium-dose prescription. And then the smaller lesions, we would give SRS normally, one session, 24 gray. At that point, we used 23 gray as our regular prescription for these situations. Those escalated, so conform with that in a conformal art therapy we used at that point. And we figured out that there was one lesion that's pretty close to the brainstem. And we saw, okay, we have to reduce those there just to be sure that we are within the constraints that we have for a brainstem, that we don't give too much dose to the brainstem.
So we have a case that's got everything in there as we thought. And our way of dealing with that in the stem, first of all, we do the single shot. And normally we include already the cavity with first fraction, so with the first 5 gray to the cavity will be included with the single-shot using brain metastases, multiple brain metastases element. You have heard about that already. So virtual isocenter somewhere in the center of mass from all lesions, so when we give all the dose. And then we include the cavity as well just to be sure that we do not get just some scavengers also. So something really calculated, something planned that we really are sure that we gave 5 gray there.
We use 4 table kicks in this situation to see how it looks here. So this will be the 5 gray isodose line going to the cavity here. You can see that's nicely conformable. Here we have the lesions just to give you an overview about that and the DVH. So, you see all your lesions are here. This is the 20 gray lesion, nice escalation over there and 5 gray medium prescription is here. So you see that we have a medium of 5 gray to the cavity that we gave.
And so the overall conformity index, even though we heard from Mr. Yamamoto maybe this might not be the right point to look at, but at least this is some kind of number we have an idea we can look to compare our plans as given here, so 1.4 are good. We excluded the cavity because of this situation it doesn't make sense to look at that given the prescription regime. So V12 is also given there in 3 gray if you want just to get an idea about [inaudible 00:04:35.731].
For the cavity then, we do some hybrid plans. So we do the cranial SRS situation, we use the software from Brainlab. This was the old one, version 1.0 because it was done one year ago. And now we do it with 1.5, which is even nicer, it leads to even nicer dose distributions. And then we give the dose there. The DVH is too bright so you can see. So what we do, we included the situation as organs at risk, also the other PTVs. So the other lesions we used to be sure to lower the dose there as much as possible. So we decided to give at least, as a maximum, 1 gray. And in this situation, see the turning point is red because it was 1.2, but it was still very, very low. You could see the deviation in those therapies.
One table angle to avoid any interference with the table angles we used before. So this would be something that we even use in Eclipse maybe with one table. So to give you an idea that really works, so here's the follow-up. People come into our institution every three months for follow-up and we will do an MRI on them, and the last one was in June this year. And you see that the lesions are gone or at least controlled. And even the cavity shrinks, as it should be, and does not do anything. So the patient is under control, still working, still living, still doing good. So something that we might have passed if he had a little radiotherapy just a couple of years ago.
So but when we want to do something like that, we have to think about...this is dose planning. So this looks nice, but we have to give the dose to the patient at least. So, does it make sense to have good planning but then to have no possibility to really give it to the patient? So the delivery must be as good as well. So we heard yesterday a lot about this. We heard something about ExacTrac. We will have some nice presentations today about ExacTrac as well. So I will just give you an idea about what different kinds of imaging solutions are out there. And then I just thought, okay, let's see. Let's do a little check. And we got the ExacTrac system. So the brain operation, you all do that. It's 2D image pairs, so 2 orthogonal x-ray images, room-based, which is the nice point, the best point about the system. So it's not gantry-based, so it doesn't matter which couch angle, table angle you use in all these two images.
We have Cone Beam CT, 3D image set, you all knew that it's Linac-based. And the other option, which at least is a little bit like imaging, would be the OSMS, so optical surface scanning, so like Varian, for instance, which will be ExacTrac Dynamic as well. So you look at the surface, you've got an open mask. You look at the nose tip more or less, and see how it moves, and then decide If you had to correct that.
And then we just had a little comparison chart to see what might be the best about everything or so, and what are the options that the system offers. And we can see here, so ExacTrac is at least our choice. Cone Beam was not a choice at all because you cannot use any non-coplanar arcs at that point. OSMS might be a choice as well if you believe that what happens on the outside is still also what happens on the inside. And I'm not sure if we really want to believe that because, I mean, it's just a sort of data. But you can decide on your own, at least. If you've got this, you should work with virtualizers and all. So that's just my message at this point.
Now, just because...we get rotational errors, right. And we saw that already. And this is just an example of some data from our institution. Typical case that I fooled around with the type of data, you can see maybe that leave openings are already not really completely filling through the lesion to the blue one or the orange one. And then if you look at the DVH for the blue lesion, just to have an idea. If you have to introduce arrows which grow, which will be there when the patient just moves a little bit on the couch, you can see how the deviation decreases. So one degree already is large compared to...the two degrees is even larger.
So one idea could be to just aim at the margin, which might be a solution for that, but we heard yesterday just already adding a margin of 1 millimeter will almost double the amount of dose or the volume. So you will give a lot of dose to healthy tissue. So you have to have another idea, so. And ExacTrac can at least handle that. So there's a nice presentation out there you can look at. They really made a good job on that. So I really would recommend to look at that so that you can have an idea. So they introduced this, I will just skip this because there are a lot of presentations already focusing on that, just that in the end, the take-home message is Exactrac can correct for this with the extra images.
So now something maybe a little bit off-topic to my talk so far. But our idea was then in the end...we started using this software in 2015, in the middle of 2015 already. And in the beginning, we just created plans and thought, "Okay, this is okay." But we had no idea of comparison because we had no way to plan quality factors. I mean, there were gradient index out there, conformity index, for sure. V10, V12, maybe you want to look at, but how do we compare that with...what data should we compare that? Because they weren't building that base data at all. So we just created all the plans. And looking at....this software always produces plans that are clinically acceptable. But what's the best plan?
And so we looked into our numbers, our data. And first of all, maybe just to get get back into your mind. So there's a risk of radionecrosis in the V10 gray or the V12 gray, which is more or less the same because you can...they are dependent on each other. [inaudible 00:10:36.435] and the papers states or, more or less, it says if you have a V10 gray for the normal brain, for the healthy brain that's over 10.5 cc, you should go for hypofractionated treatment because the risk of radionecrosis will increase a lot. But most of the papers or almost all the papers out there are just focusing on single lesions. So this is data for a single lesion.
Now we do something completely different, we have a game-changer, we're looking at multiple lesions. So we have to have an idea of what is that. Radionecrosis is a localized effect, so it's always happening in the high-dose area around the lesion. So looking at the V10 gray or the V12 gray for the whole brain, we're treating 20 lesions, 50 lesions, whatever, it doesn't make sense at all. But it's the only number we have so far. So at that point, we decided, let's do some statistics, at least. So these were the first patients that we treated already in our execution, so not all but the first that we did some statistics on. And we look at the brain volume receiving 10 gray, so the V10 gray for the brain, and compared that to the total PTV volume.
So first of all, we want to get rid of the number of lesions because that's not a good predictor at all. So, at the end, it's just tumor volume that counts. It doesn't matter if it's 1 lesion or it's 10 lesions, as long as you have the same tumor volume, it's more or less the same dose we will give. So the total tumor volume came up with this nice linear thing here. And you see we've got some plans over there. So if they were worse, we get more brain...more models to the brain than we were able to do for other lesions, so for other situations. In the end, you also see that our total proven PTV volume is quite low. So we treat a lot of small lesions, not very large lesions, but most of them are small lesions.
And this is everything that nowadays a plan has to be benchmarked against. So whenever we do a plan with software, we have some experience right now. Every plan has to be at least on the curve or below the curve. So this is the way we want to go in this situation. We do the same for the conformity index. But I can also show you the curve of gradient index, which we also yesterday heard a little debate on if that's a good number or not. In the end, it's at least one of the numbers we have, so we put it down here. And normally the literature says a gradient index of 3 would be perfect. So we're not exactly at 3, but a lot of our lesions are around 4 again. Now, this is the individual tumor volume. And you see, most of all our tumors are between 0 and 2cc. So we are really treating quite new lesions, small lesions. That's possible because we have good neurosurgery, good neuroradiology department, we've got good images, and so on. And this is also the benchmark that every plan, at least, has to be calculated against.
To give you an idea about how we, at least, performed against the literature, last year there was a paper published here. They were looking, I think, at the [inaudible 00:13:40.770] to brain metastases and compare that and looked at whether it's achievable. And their gradient index and conformity index is here, and this is how we do right now. So we are pretty close to 1. As everyone would say, this would be a perfect conformity index and [inaudible 00:13:57.986]. So we are quite nicely in the area of 1. And again, this is for multiple metastases with a single isocenter. When we use plain SRS, we are really almost at 1 right now. So we're really touching one. So the software is really doing a good job.
So yeah, here's just my conclusion in the end of just what I would really say if you want to do something like that, you really have to think about the whole chain. So it's not just dose calculation in the end, it's really image guidance that guides us there and that really helps us to deliver at least what we want to give. It's not just calculation. So yeah, thank you for your attention.
First of all, we have to reconsider or have to consider, what would we call a complex planning situation? And I just wrote down three points that came into my mind. And the first one was, okay, maybe when they have a large number of lesions, clustered or not. We heard a lot about that yesterday already. The second point would be maybe if we got different prescription regimes, so we got maybe a large lesion, but we want to give fractionated SRS or SRT. And maybe we have got some SRS as well, some single shot, or we want to go to the high dose in one session, so that might make the situation a little bit complex. And the third thing that came into my mind was maybe if we got different indications. So we got maybe multiple lesions, just multiple brain metastases, and one was the surgery maybe because it was quite large. And then the neurosurgeon has decided, "Okay, we'll take that out." And then we have to irradiate the cavity as well.
So then I thought, okay, let's talk about that. And then I picked just one case out of our clinic, and I thought, "Okay, why not put it all together in one case?" And this is a typical case we have. So this is the 50-year-old male patient, got lump cell, first diagnosed, six brain metastases in July last year. And so here's just an overview of the software, that we have an idea where they were positioned. And one was a very large one, so they got rejected by our neurosurgeons in the hospital. And the patient came to us and they said, "Okay, let's do something about that. You have to irradiate that. We want to be sure that everything is okay." And we said, "Yeah, sure we can make it."
And then we looked at the images and thought, okay, this might be the fractionated thing because if the cavity is still normal, we get 7 times 5 gray to that, like an ICRU conformable medium-dose prescription. And then the smaller lesions, we would give SRS normally, one session, 24 gray. At that point, we used 23 gray as our regular prescription for these situations. Those escalated, so conform with that in a conformal art therapy we used at that point. And we figured out that there was one lesion that's pretty close to the brainstem. And we saw, okay, we have to reduce those there just to be sure that we are within the constraints that we have for a brainstem, that we don't give too much dose to the brainstem.
So we have a case that's got everything in there as we thought. And our way of dealing with that in the stem, first of all, we do the single shot. And normally we include already the cavity with first fraction, so with the first 5 gray to the cavity will be included with the single-shot using brain metastases, multiple brain metastases element. You have heard about that already. So virtual isocenter somewhere in the center of mass from all lesions, so when we give all the dose. And then we include the cavity as well just to be sure that we do not get just some scavengers also. So something really calculated, something planned that we really are sure that we gave 5 gray there.
We use 4 table kicks in this situation to see how it looks here. So this will be the 5 gray isodose line going to the cavity here. You can see that's nicely conformable. Here we have the lesions just to give you an overview about that and the DVH. So, you see all your lesions are here. This is the 20 gray lesion, nice escalation over there and 5 gray medium prescription is here. So you see that we have a medium of 5 gray to the cavity that we gave.
And so the overall conformity index, even though we heard from Mr. Yamamoto maybe this might not be the right point to look at, but at least this is some kind of number we have an idea we can look to compare our plans as given here, so 1.4 are good. We excluded the cavity because of this situation it doesn't make sense to look at that given the prescription regime. So V12 is also given there in 3 gray if you want just to get an idea about [inaudible 00:04:35.731].
For the cavity then, we do some hybrid plans. So we do the cranial SRS situation, we use the software from Brainlab. This was the old one, version 1.0 because it was done one year ago. And now we do it with 1.5, which is even nicer, it leads to even nicer dose distributions. And then we give the dose there. The DVH is too bright so you can see. So what we do, we included the situation as organs at risk, also the other PTVs. So the other lesions we used to be sure to lower the dose there as much as possible. So we decided to give at least, as a maximum, 1 gray. And in this situation, see the turning point is red because it was 1.2, but it was still very, very low. You could see the deviation in those therapies.
One table angle to avoid any interference with the table angles we used before. So this would be something that we even use in Eclipse maybe with one table. So to give you an idea that really works, so here's the follow-up. People come into our institution every three months for follow-up and we will do an MRI on them, and the last one was in June this year. And you see that the lesions are gone or at least controlled. And even the cavity shrinks, as it should be, and does not do anything. So the patient is under control, still working, still living, still doing good. So something that we might have passed if he had a little radiotherapy just a couple of years ago.
So but when we want to do something like that, we have to think about...this is dose planning. So this looks nice, but we have to give the dose to the patient at least. So, does it make sense to have good planning but then to have no possibility to really give it to the patient? So the delivery must be as good as well. So we heard yesterday a lot about this. We heard something about ExacTrac. We will have some nice presentations today about ExacTrac as well. So I will just give you an idea about what different kinds of imaging solutions are out there. And then I just thought, okay, let's see. Let's do a little check. And we got the ExacTrac system. So the brain operation, you all do that. It's 2D image pairs, so 2 orthogonal x-ray images, room-based, which is the nice point, the best point about the system. So it's not gantry-based, so it doesn't matter which couch angle, table angle you use in all these two images.
We have Cone Beam CT, 3D image set, you all knew that it's Linac-based. And the other option, which at least is a little bit like imaging, would be the OSMS, so optical surface scanning, so like Varian, for instance, which will be ExacTrac Dynamic as well. So you look at the surface, you've got an open mask. You look at the nose tip more or less, and see how it moves, and then decide If you had to correct that.
And then we just had a little comparison chart to see what might be the best about everything or so, and what are the options that the system offers. And we can see here, so ExacTrac is at least our choice. Cone Beam was not a choice at all because you cannot use any non-coplanar arcs at that point. OSMS might be a choice as well if you believe that what happens on the outside is still also what happens on the inside. And I'm not sure if we really want to believe that because, I mean, it's just a sort of data. But you can decide on your own, at least. If you've got this, you should work with virtualizers and all. So that's just my message at this point.
Now, just because...we get rotational errors, right. And we saw that already. And this is just an example of some data from our institution. Typical case that I fooled around with the type of data, you can see maybe that leave openings are already not really completely filling through the lesion to the blue one or the orange one. And then if you look at the DVH for the blue lesion, just to have an idea. If you have to introduce arrows which grow, which will be there when the patient just moves a little bit on the couch, you can see how the deviation decreases. So one degree already is large compared to...the two degrees is even larger.
So one idea could be to just aim at the margin, which might be a solution for that, but we heard yesterday just already adding a margin of 1 millimeter will almost double the amount of dose or the volume. So you will give a lot of dose to healthy tissue. So you have to have another idea, so. And ExacTrac can at least handle that. So there's a nice presentation out there you can look at. They really made a good job on that. So I really would recommend to look at that so that you can have an idea. So they introduced this, I will just skip this because there are a lot of presentations already focusing on that, just that in the end, the take-home message is Exactrac can correct for this with the extra images.
So now something maybe a little bit off-topic to my talk so far. But our idea was then in the end...we started using this software in 2015, in the middle of 2015 already. And in the beginning, we just created plans and thought, "Okay, this is okay." But we had no idea of comparison because we had no way to plan quality factors. I mean, there were gradient index out there, conformity index, for sure. V10, V12, maybe you want to look at, but how do we compare that with...what data should we compare that? Because they weren't building that base data at all. So we just created all the plans. And looking at....this software always produces plans that are clinically acceptable. But what's the best plan?
And so we looked into our numbers, our data. And first of all, maybe just to get get back into your mind. So there's a risk of radionecrosis in the V10 gray or the V12 gray, which is more or less the same because you can...they are dependent on each other. [inaudible 00:10:36.435] and the papers states or, more or less, it says if you have a V10 gray for the normal brain, for the healthy brain that's over 10.5 cc, you should go for hypofractionated treatment because the risk of radionecrosis will increase a lot. But most of the papers or almost all the papers out there are just focusing on single lesions. So this is data for a single lesion.
Now we do something completely different, we have a game-changer, we're looking at multiple lesions. So we have to have an idea of what is that. Radionecrosis is a localized effect, so it's always happening in the high-dose area around the lesion. So looking at the V10 gray or the V12 gray for the whole brain, we're treating 20 lesions, 50 lesions, whatever, it doesn't make sense at all. But it's the only number we have so far. So at that point, we decided, let's do some statistics, at least. So these were the first patients that we treated already in our execution, so not all but the first that we did some statistics on. And we look at the brain volume receiving 10 gray, so the V10 gray for the brain, and compared that to the total PTV volume.
So first of all, we want to get rid of the number of lesions because that's not a good predictor at all. So, at the end, it's just tumor volume that counts. It doesn't matter if it's 1 lesion or it's 10 lesions, as long as you have the same tumor volume, it's more or less the same dose we will give. So the total tumor volume came up with this nice linear thing here. And you see we've got some plans over there. So if they were worse, we get more brain...more models to the brain than we were able to do for other lesions, so for other situations. In the end, you also see that our total proven PTV volume is quite low. So we treat a lot of small lesions, not very large lesions, but most of them are small lesions.
And this is everything that nowadays a plan has to be benchmarked against. So whenever we do a plan with software, we have some experience right now. Every plan has to be at least on the curve or below the curve. So this is the way we want to go in this situation. We do the same for the conformity index. But I can also show you the curve of gradient index, which we also yesterday heard a little debate on if that's a good number or not. In the end, it's at least one of the numbers we have, so we put it down here. And normally the literature says a gradient index of 3 would be perfect. So we're not exactly at 3, but a lot of our lesions are around 4 again. Now, this is the individual tumor volume. And you see, most of all our tumors are between 0 and 2cc. So we are really treating quite new lesions, small lesions. That's possible because we have good neurosurgery, good neuroradiology department, we've got good images, and so on. And this is also the benchmark that every plan, at least, has to be calculated against.
To give you an idea about how we, at least, performed against the literature, last year there was a paper published here. They were looking, I think, at the [inaudible 00:13:40.770] to brain metastases and compare that and looked at whether it's achievable. And their gradient index and conformity index is here, and this is how we do right now. So we are pretty close to 1. As everyone would say, this would be a perfect conformity index and [inaudible 00:13:57.986]. So we are quite nicely in the area of 1. And again, this is for multiple metastases with a single isocenter. When we use plain SRS, we are really almost at 1 right now. So we're really touching one. So the software is really doing a good job.
So yeah, here's just my conclusion in the end of just what I would really say if you want to do something like that, you really have to think about the whole chain. So it's not just dose calculation in the end, it's really image guidance that guides us there and that really helps us to deliver at least what we want to give. It's not just calculation. So yeah, thank you for your attention.