Transcript
Thank you for having me here. It's always nice to have a Munich conference and to have so many people from around the world here, and show you what we in Munich do. So, I'm here today to talk to you about the frameless radiosurgery accuracy for Elekta configurations, which is basically an overview of how we managed to get high accurate treatment at our clinic, for a frame of ExacTrac installed on Elekta LINAC.
So, this is what we got. I have a little bit to disclose to you. We have received some research grants from Brainlab. Just a short introduction of my department under Professor Erker. We have roughly 2,000 patients a year in two headquarters. One in Großhadern, which is a little bit outside of Munich, and one in the city center. We have six LINACs in total, and we are waiting to get an MRI-LINAC hopefully. Yeah. The plan is already on. We are already a little bit behind. It's just the construction has already been started. We have various options of image guidance in our clinic, pretty much everything there is for Elekta sites, including the MRI-LINAC soon, and we also have a lot of different treatment planning systems. We do pretty much any technique. I'm not including brachytherapy here, which we also do. All the established methods and large-field techniques of radiotherapy.
And now, this is the key of the talk. Actually, one of the requirements for modern radiosurgery at the moment? We don't have any role for rigid patient fixation anymore with new modern techniques and machines. We don't have any role for fiducials anymore. Of course, as we just have seen, before long radiation can reduces patient comfort, treatment resistance. And, of course, from a financial point of view, the capacity of the treatment unit. So, you want to get rid of that a long time. How we do our stereotactic treatments. At LMU Munich, we have, of course, a big MRI. We use MRI. We also have a double-layer mask. We do a planning CT with contrast. We calculate everything on a 2-millimeter dose grid. We have a 2-millimeter margin to the GTV, as we have roughly a gantry deviation of 0.5 millimeters, and a couch deviation of uncertainties of 0.7 millimeters. We do both dynamic conformal arc in Flattening Filter Free, 10MV. We have four to six partial non-coplanar arcs. As for the dose rate in dynamic conformal arc per partial arc is constant, but it's different from the individual arcs. And we have a dose rate that reaches 2,400 monitor units a minute with FFF.
We have also apart from the single stereotactic treatments, we have, the so-called stereobrain. I don't know if somebody had the chance to listen to Dr. Niyazi? Yesterday, he talked a lot about this project. So, basically, we just want to compare whole-brain radiotherapy with stereotactic radiosurgery for patients with 4 to 10 metastases. I'm not going to talk in too much detail about it. You might have heard that yesterday, but these are all some of the Elements Multiple BrainMets SRS, and this has been talked a lot here. So, we have highly, highly complex plans. As you see before, the other talks already, this is what the plan would look like if irradiated. So, multiple metastases are irradiated in one part, and all the way back there is a little bit other metastases irradiated. So, when you have your highly complex plans which you, sort of, need to get a good feeling, especially as a physicist to apply.
So, what could go wrong eventually? If you...That's pretty much nothing new. If you aim at the PTV, it does not automatically mean you hit the target. And, you know, some geometrical certainties, which result in potential different isocenters. So, how would that look like on our LINAC? We have one isocenter of the laser. We have one isocenter of the gantry. And then after you get the collimator, you have your beam. Eventually, you have the imaging system, and which is quite important for these stereotactic non-coplanar techniques you have in the isocenter of the couch, and of the deviations there. Now, I was faster than the animation. Good. Frame-based radiosurgery, how we used to do it, the classical head ring fixed to the skull, bones, or [inaudible 00:05:06] as we say it here, or everywhere, pretty much. We positioned the stereotactic frame according to the in-room lasers. Why would you...why is there a need for interchangeable couch angles? You have quite...You can see it in the light here. This shift from the laser to the couch is what drives a technician mad, or as a physicist also. So, he would correct this with this error thing with a micrometer screw for transitions and tilt.
How do we do it nowadays? Or at the moment with Elekta in combination with the ExacTrac? So we have a Versa HD. You have a 160 MLC LINAC, with quite high leaf speed, the collimator speed. As we heard before, 0.5 centimeters projected leaf width at the isocenter. What is also very important is, I have a general table which is...which you can correct in six different, I forgot the word, degrees of freedom, translation, and rotation. And finally, we have the Brainlab system. So, we have a room-integrated, X-ray-based supervision, which allows us to have a position verification based on the anatomy of the patient. And, we supervise the patient during the whole radiotherapy session or fraction, and we can also calculate the intra-fractional deviations regardless, and that's the most important part of it, as you heard before, of the couch angle, or of the gantry angle. So, these are, again, some...one or two pictures of, which belong to Brainlab because they have the licensed pictures, of course, of their system. We have fully automatic and remote six-dimensional positioning of the robotic couches, and we also have multi-market game hold in this case.
So, in general, accuracy, as you heard before, for all systems, not necessarily Elekta configurations, we are, in general, smaller than mean below 1 millimeter, and just confirmed through our literature for the system. How will it look like with non-coplanar imaging? So, there is a study that shows that met roughly 1,000 setups with different angles of couch and gantry, and they said the mean intra-fractional below 1 millimeter, only 12% of all intra-fractional values of three dimensions were above 1 millimeter, which made us quite happy in our case. How do we do it with the Elekta configurations? So, here in Munich, we had the pilot installation of an ExacTrac, Elekta-ExacTrac, with a Versa HD, which you can see over there. Now, we want to see, we have a cone beam CT. This is our gold standard, obviously, not for all couch angles, but this is our gold standard here. We have our cone beam CT. How accurate is the positioning of the ExacTrac system compared to the cone-beam CT which we believe in, and which we trust in our case? And so we did that for...we compared the positioning errors of the cone beam CT with those resulting from the ExacTrac for 32 patients, and in addition, we had ball-bearing and head phantom tests on the LINAC.
And what did we get? So, we have a close agreement that the stereoscopic X-ray imaging from ExacTrac and our cone beam CT in all directories, and we have neglected the cross-modal discrepancies in the position detection of all the patients. In the control phantom measurements, we have accuracy and precision of below 0.1 millimeters. So, we are pretty much happy to use the system, and especially as plans get more and more complex pretty much every day. Some rumors that 15 metastases to treat in one session might not be enough. This number could go up in the future, maybe. So, as we've seen before, rotational errors of that kind can be too huge discrepancies between what you plan and what you get at the end.
So, overall, I'm a little early already. Maybe I was talking a little fast for the moment. As we said, fiducials and rigid patient fixation. If you have the requirements for any other machines, and obviously, the money to buy systems like that, in modern techniques, obsolete at the moment. As we've seen, one LINAC has multiple isocenters, gantry, collimator, couch, and the imaging system, and so on. We always have to account, and obviously, [inaudible 00:10:22] said you have to measure these errors with regular per hour, from month to month, week to week, or day to day. You can account for these errors with X-ray supervision during the whole fractions, and for all possible couch and gantry angles. You can perform frameless radiosurgery with an accuracy of a mean, or what everybody, sort of, agrees on, a mean accuracy of 1.0 millimeters, which is pretty much in all of the...good for all of the PTV margins we apply to our GTVs. And for Elekta configurations, we have shown that the stereoscopic X-ray imaging is in good agreement with our kV-cone beam CT, with the distinct advantages of having imaging at all gantry and couch angles. So, thank you very much.
So, this is what we got. I have a little bit to disclose to you. We have received some research grants from Brainlab. Just a short introduction of my department under Professor Erker. We have roughly 2,000 patients a year in two headquarters. One in Großhadern, which is a little bit outside of Munich, and one in the city center. We have six LINACs in total, and we are waiting to get an MRI-LINAC hopefully. Yeah. The plan is already on. We are already a little bit behind. It's just the construction has already been started. We have various options of image guidance in our clinic, pretty much everything there is for Elekta sites, including the MRI-LINAC soon, and we also have a lot of different treatment planning systems. We do pretty much any technique. I'm not including brachytherapy here, which we also do. All the established methods and large-field techniques of radiotherapy.
And now, this is the key of the talk. Actually, one of the requirements for modern radiosurgery at the moment? We don't have any role for rigid patient fixation anymore with new modern techniques and machines. We don't have any role for fiducials anymore. Of course, as we just have seen, before long radiation can reduces patient comfort, treatment resistance. And, of course, from a financial point of view, the capacity of the treatment unit. So, you want to get rid of that a long time. How we do our stereotactic treatments. At LMU Munich, we have, of course, a big MRI. We use MRI. We also have a double-layer mask. We do a planning CT with contrast. We calculate everything on a 2-millimeter dose grid. We have a 2-millimeter margin to the GTV, as we have roughly a gantry deviation of 0.5 millimeters, and a couch deviation of uncertainties of 0.7 millimeters. We do both dynamic conformal arc in Flattening Filter Free, 10MV. We have four to six partial non-coplanar arcs. As for the dose rate in dynamic conformal arc per partial arc is constant, but it's different from the individual arcs. And we have a dose rate that reaches 2,400 monitor units a minute with FFF.
We have also apart from the single stereotactic treatments, we have, the so-called stereobrain. I don't know if somebody had the chance to listen to Dr. Niyazi? Yesterday, he talked a lot about this project. So, basically, we just want to compare whole-brain radiotherapy with stereotactic radiosurgery for patients with 4 to 10 metastases. I'm not going to talk in too much detail about it. You might have heard that yesterday, but these are all some of the Elements Multiple BrainMets SRS, and this has been talked a lot here. So, we have highly, highly complex plans. As you see before, the other talks already, this is what the plan would look like if irradiated. So, multiple metastases are irradiated in one part, and all the way back there is a little bit other metastases irradiated. So, when you have your highly complex plans which you, sort of, need to get a good feeling, especially as a physicist to apply.
So, what could go wrong eventually? If you...That's pretty much nothing new. If you aim at the PTV, it does not automatically mean you hit the target. And, you know, some geometrical certainties, which result in potential different isocenters. So, how would that look like on our LINAC? We have one isocenter of the laser. We have one isocenter of the gantry. And then after you get the collimator, you have your beam. Eventually, you have the imaging system, and which is quite important for these stereotactic non-coplanar techniques you have in the isocenter of the couch, and of the deviations there. Now, I was faster than the animation. Good. Frame-based radiosurgery, how we used to do it, the classical head ring fixed to the skull, bones, or [inaudible 00:05:06] as we say it here, or everywhere, pretty much. We positioned the stereotactic frame according to the in-room lasers. Why would you...why is there a need for interchangeable couch angles? You have quite...You can see it in the light here. This shift from the laser to the couch is what drives a technician mad, or as a physicist also. So, he would correct this with this error thing with a micrometer screw for transitions and tilt.
How do we do it nowadays? Or at the moment with Elekta in combination with the ExacTrac? So we have a Versa HD. You have a 160 MLC LINAC, with quite high leaf speed, the collimator speed. As we heard before, 0.5 centimeters projected leaf width at the isocenter. What is also very important is, I have a general table which is...which you can correct in six different, I forgot the word, degrees of freedom, translation, and rotation. And finally, we have the Brainlab system. So, we have a room-integrated, X-ray-based supervision, which allows us to have a position verification based on the anatomy of the patient. And, we supervise the patient during the whole radiotherapy session or fraction, and we can also calculate the intra-fractional deviations regardless, and that's the most important part of it, as you heard before, of the couch angle, or of the gantry angle. So, these are, again, some...one or two pictures of, which belong to Brainlab because they have the licensed pictures, of course, of their system. We have fully automatic and remote six-dimensional positioning of the robotic couches, and we also have multi-market game hold in this case.
So, in general, accuracy, as you heard before, for all systems, not necessarily Elekta configurations, we are, in general, smaller than mean below 1 millimeter, and just confirmed through our literature for the system. How will it look like with non-coplanar imaging? So, there is a study that shows that met roughly 1,000 setups with different angles of couch and gantry, and they said the mean intra-fractional below 1 millimeter, only 12% of all intra-fractional values of three dimensions were above 1 millimeter, which made us quite happy in our case. How do we do it with the Elekta configurations? So, here in Munich, we had the pilot installation of an ExacTrac, Elekta-ExacTrac, with a Versa HD, which you can see over there. Now, we want to see, we have a cone beam CT. This is our gold standard, obviously, not for all couch angles, but this is our gold standard here. We have our cone beam CT. How accurate is the positioning of the ExacTrac system compared to the cone-beam CT which we believe in, and which we trust in our case? And so we did that for...we compared the positioning errors of the cone beam CT with those resulting from the ExacTrac for 32 patients, and in addition, we had ball-bearing and head phantom tests on the LINAC.
And what did we get? So, we have a close agreement that the stereoscopic X-ray imaging from ExacTrac and our cone beam CT in all directories, and we have neglected the cross-modal discrepancies in the position detection of all the patients. In the control phantom measurements, we have accuracy and precision of below 0.1 millimeters. So, we are pretty much happy to use the system, and especially as plans get more and more complex pretty much every day. Some rumors that 15 metastases to treat in one session might not be enough. This number could go up in the future, maybe. So, as we've seen before, rotational errors of that kind can be too huge discrepancies between what you plan and what you get at the end.
So, overall, I'm a little early already. Maybe I was talking a little fast for the moment. As we said, fiducials and rigid patient fixation. If you have the requirements for any other machines, and obviously, the money to buy systems like that, in modern techniques, obsolete at the moment. As we've seen, one LINAC has multiple isocenters, gantry, collimator, couch, and the imaging system, and so on. We always have to account, and obviously, [inaudible 00:10:22] said you have to measure these errors with regular per hour, from month to month, week to week, or day to day. You can account for these errors with X-ray supervision during the whole fractions, and for all possible couch and gantry angles. You can perform frameless radiosurgery with an accuracy of a mean, or what everybody, sort of, agrees on, a mean accuracy of 1.0 millimeters, which is pretty much in all of the...good for all of the PTV margins we apply to our GTVs. And for Elekta configurations, we have shown that the stereoscopic X-ray imaging is in good agreement with our kV-cone beam CT, with the distinct advantages of having imaging at all gantry and couch angles. So, thank you very much.