Transcript
Hello, everyone, and welcome to ASTRO's 2020 Expert Demo Session. My name is Bogdan Valcu, and today I have the privilege to introduce to you Professor Nzhde Agazaryan from UCLA. Dr. Agazaryan is a Professor of Physics and Biology in Medicine at UCLA. He's also the Chief of Clinical Medical Physics and Dosimetry, and serves as the quality and safety officer.
Professor Agazaryan is also a Novalis Circle expert, and today he will be reviewing the latest developments for our Elements Multiple Brain Mets SRS product line. Over the years, we've had the privilege to work with the UCLA group on all our versions of Elements Multiple Brain Mets SRS, and today Professor Agazaryan will be reviewing his experience with the product as well as highlight some of the new developments in the 3.0 upcoming platform.
We are proud to continue to introduce tools that help with the automation of the software. And in his review, Dr. Agazaryan will touch on the new 4Pi optimization for trajectory selection, review algorithmic improvements to help with bridging dosing between targets, showcase the benefits of new tools such as jaw tracking for variant MLCs, and discuss overall planning efficiency parameters, such as automatic margin, definition, and plan qualifiers.
As of October 2020, Elements Multiple Brain Mets SRS 3.0 has a pending commercial availability. So, please check with your local sales representative for when the product will be available in your market. And now I'd like to turn it over to Dr. Agazaryan for his lecture.
Dr. Agazaryan: Thank you, Bogdan, for the introduction. I will be presenting on the UCLA experience with the single isocenter treatment technique for multiple brain metastases and improvements in Elements Multiple Brain Mets SRS 3.0. These are my disclosures. The implementation of the single isocenter treatment technique at our institution had a significant impact on patient experience, provider benefits, and treatment unit throughput.
As shown in this seven-lesion treatment case, the benefits are pretty significant. And these benefits increase incrementally per additional lesion. Here's one specific area of time-saving I show here. Treatment planning time as a function of number of lesions treated with single isocenter versus multiple isocenters, these time savings are really significant. There's also cost savings associated with the application of this treatment method.
Recently in June 2020, we have published a study in a rad journal, where we have used time-driven, activity-based costing to determine the difference in cost to provider using the SRS single isocenter technique versus multiple isocenter technique. Here in this graph, we show cost savings when we deliver SRS with one technique, compared to the other one.
Obviously, the cost savings increase with the number of lesions treated. I should also share with you that we have also extensively investigated the dosimetric and geometric accuracy of the system in the past. In this one example I show here, the ion chamber validation is used with a water-fillable phantom. This phantom is a good candidate for periodic QA and it has three ion chambers in it.
Here's the example plan created to deliver 14 Gray, 16 Gray, and 18 Gray prescriptions to the ion chamber locations. And in this graph, what we show is the percent difference between the measurement and calculation for each of the ion chamber measurements. The maximum deviation from the measurement is less than 2%. So, this is a pretty good validation with an absolute dose. We have also validated the system with RT Safe Gel Phantom.
And here I show an example, a profile going to the coronal plane showing an excellent agreement between calculation and measurement. The orange line on the graph is the planned dose profile, and the blue line is the measured profile. And as you can see, they're almost indistinguishable. Most importantly, our institution has shown great clinical outcomes with single-arm retrospective study. We show excellent local control and freedom from radionecrosis. This is the first arm of the study.
The second arm of the study, which is the multiple isocenter treatment, is still being conducted, and then we will be comparing the first arm to the second arm. With this great experience and results came some newly discovered or remaining challenges. For example, dose compactness when the targets are close to each other, is there an opportunity to further improve the compactness and separate the distributions like this?
Also, the calculations of the plan qualifiers, the local and global plan qualifiers, for example, how to get V12 values for situations shown in this picture here. Also, the optimization of arcs and table positions. You don't necessarily need to use the five table angles that are typically programmed in templates. Also, shown in this picture here, the automatic generation of variable margins. Many institutions would like to generate different margins based on the distance from the isocenter.
And as shown in this picture here, the dynamic geo-tracking for varying units, which was previously not available in the Elements. So, Brainlab has recently introduced their Multiple Brain Metastases version 3.0. It includes 4Pi optimization, which is the most impactful algorithm change in this version. This algorithm strategically reduces the table positions or actually adds table positions if needed to improve the dose distribution.
Here we show an example where the reduced number of table positions and arcs did not actually compromise the quality of the plan. So, this is the four-arc plan given by the 4Pi optimization, and this is the plan given by the template. And as you can see, the target coverage, the OER sparing, as well as the normal brain overall, those are almost identical.
With regards to those bridging, the DCA complexity slider has been further enhanced to close the treatment fields when the beam's eye view of target is actually covering another target. The software will close the fields only for the mets and situations where the dose distribution is improved. And here's an example of the use of DCA, very clear dosimetric benefit is seen with the use of this option. So, if you use DCA complexity high, then the dose distribution starts separating.
So, related to this subject, the new version of the Elements calculates local values for each of the contiguous dose distributions. This version of the Elements creates a ring object and each of the targets not seen by the planner. This is to produce the V8, V12, and V10 values. This is clearly an important tool for clinical use. We will see examples of this kind of data previously generated manually by UCLA. Now it can be done automatically.
So, here's an example showing the MLC field closes as one target beam's eye view is covering the other one. Switching gears, the dynamic jaw tracking has been implemented for very linear accelerators in this version of Elements. This is an important and useful option for multiple metastases. It makes plans better in terms of reducing the normal tissue dose by reducing the leakage throughout these areas here. For each gantry position, the jaw comes closer to the field, the field edge, and minimizes the leakage dose.
So, now, let's talk about the automatic margin generation based on the distances from the isocenter as mentioned previously. As seen in this animation here, rotations have larger impact for targets that are further away from the isocenter. Institutions either use or intend to use different margins for the target's different distances from the isocenter.
It's extremely important to use minimum margins for these treatments because, as shown in this study, if you add one-millimeter margin and two-millimeter margin, you essentially double and triple the endpoints of V5, V8, and, V10, and V12. So, reducing margins improves that, using variable margins also improves that. The variable margin could be an important approach because only small percent of the targets are typically far away from the isocenter.
In this quick study, only 10 or 15% of the targets were more than 6cm away from the isocenter. So, there is no need to introduce larger margins for all of the other targets that are nearby the isocenter. I should mention that using larger margins can also impact the prescription dose if one follows the consensus guidelines. Depending on the clinical prescription strategy, about 10% or 15% of the targets that are at the sort of periphery of this decision-making lies may get lower prescriptions.
So, we intended to use variable margins at UCLA in the past, but for various reasons including the absence of the automatic generation tool that I just described, we decided to go with a uniform one-millimeter margin all around the targets. This was obviously an improvement compared to the two-millimeter margin we used to utilize, but if now we switch to variable margin of 0.5 and one millimeter, is going to be a further improvement. This variable margin option is now available in version 3.
One can define rules for margin generation that increases linearly in terms of distance, or it can be a step-wise approach similar to what I described previously. The targets that are closer than 6cm, for example, gets smaller margins and the targets that are further away get larger margins. I should mention that one can also have automated rules based on the volumes of the targets, and we can come up with many scenarios where you could use that rule based on the volumes.
So, in this presentation, I have quickly summarized the UCLA experience with the multiple brain metastases treatment with single isocenter, and I've reviewed the enhancements in Elements Multiple Brain Metastases SRS 3.0. I thank you for your attention.
Bogdan: Thank you very much for your lecture, Dr. Agazaryan, and thank you all for your participation. And please, enjoy the Virtual 2020 ASTRO.
Professor Agazaryan is also a Novalis Circle expert, and today he will be reviewing the latest developments for our Elements Multiple Brain Mets SRS product line. Over the years, we've had the privilege to work with the UCLA group on all our versions of Elements Multiple Brain Mets SRS, and today Professor Agazaryan will be reviewing his experience with the product as well as highlight some of the new developments in the 3.0 upcoming platform.
We are proud to continue to introduce tools that help with the automation of the software. And in his review, Dr. Agazaryan will touch on the new 4Pi optimization for trajectory selection, review algorithmic improvements to help with bridging dosing between targets, showcase the benefits of new tools such as jaw tracking for variant MLCs, and discuss overall planning efficiency parameters, such as automatic margin, definition, and plan qualifiers.
As of October 2020, Elements Multiple Brain Mets SRS 3.0 has a pending commercial availability. So, please check with your local sales representative for when the product will be available in your market. And now I'd like to turn it over to Dr. Agazaryan for his lecture.
Dr. Agazaryan: Thank you, Bogdan, for the introduction. I will be presenting on the UCLA experience with the single isocenter treatment technique for multiple brain metastases and improvements in Elements Multiple Brain Mets SRS 3.0. These are my disclosures. The implementation of the single isocenter treatment technique at our institution had a significant impact on patient experience, provider benefits, and treatment unit throughput.
As shown in this seven-lesion treatment case, the benefits are pretty significant. And these benefits increase incrementally per additional lesion. Here's one specific area of time-saving I show here. Treatment planning time as a function of number of lesions treated with single isocenter versus multiple isocenters, these time savings are really significant. There's also cost savings associated with the application of this treatment method.
Recently in June 2020, we have published a study in a rad journal, where we have used time-driven, activity-based costing to determine the difference in cost to provider using the SRS single isocenter technique versus multiple isocenter technique. Here in this graph, we show cost savings when we deliver SRS with one technique, compared to the other one.
Obviously, the cost savings increase with the number of lesions treated. I should also share with you that we have also extensively investigated the dosimetric and geometric accuracy of the system in the past. In this one example I show here, the ion chamber validation is used with a water-fillable phantom. This phantom is a good candidate for periodic QA and it has three ion chambers in it.
Here's the example plan created to deliver 14 Gray, 16 Gray, and 18 Gray prescriptions to the ion chamber locations. And in this graph, what we show is the percent difference between the measurement and calculation for each of the ion chamber measurements. The maximum deviation from the measurement is less than 2%. So, this is a pretty good validation with an absolute dose. We have also validated the system with RT Safe Gel Phantom.
And here I show an example, a profile going to the coronal plane showing an excellent agreement between calculation and measurement. The orange line on the graph is the planned dose profile, and the blue line is the measured profile. And as you can see, they're almost indistinguishable. Most importantly, our institution has shown great clinical outcomes with single-arm retrospective study. We show excellent local control and freedom from radionecrosis. This is the first arm of the study.
The second arm of the study, which is the multiple isocenter treatment, is still being conducted, and then we will be comparing the first arm to the second arm. With this great experience and results came some newly discovered or remaining challenges. For example, dose compactness when the targets are close to each other, is there an opportunity to further improve the compactness and separate the distributions like this?
Also, the calculations of the plan qualifiers, the local and global plan qualifiers, for example, how to get V12 values for situations shown in this picture here. Also, the optimization of arcs and table positions. You don't necessarily need to use the five table angles that are typically programmed in templates. Also, shown in this picture here, the automatic generation of variable margins. Many institutions would like to generate different margins based on the distance from the isocenter.
And as shown in this picture here, the dynamic geo-tracking for varying units, which was previously not available in the Elements. So, Brainlab has recently introduced their Multiple Brain Metastases version 3.0. It includes 4Pi optimization, which is the most impactful algorithm change in this version. This algorithm strategically reduces the table positions or actually adds table positions if needed to improve the dose distribution.
Here we show an example where the reduced number of table positions and arcs did not actually compromise the quality of the plan. So, this is the four-arc plan given by the 4Pi optimization, and this is the plan given by the template. And as you can see, the target coverage, the OER sparing, as well as the normal brain overall, those are almost identical.
With regards to those bridging, the DCA complexity slider has been further enhanced to close the treatment fields when the beam's eye view of target is actually covering another target. The software will close the fields only for the mets and situations where the dose distribution is improved. And here's an example of the use of DCA, very clear dosimetric benefit is seen with the use of this option. So, if you use DCA complexity high, then the dose distribution starts separating.
So, related to this subject, the new version of the Elements calculates local values for each of the contiguous dose distributions. This version of the Elements creates a ring object and each of the targets not seen by the planner. This is to produce the V8, V12, and V10 values. This is clearly an important tool for clinical use. We will see examples of this kind of data previously generated manually by UCLA. Now it can be done automatically.
So, here's an example showing the MLC field closes as one target beam's eye view is covering the other one. Switching gears, the dynamic jaw tracking has been implemented for very linear accelerators in this version of Elements. This is an important and useful option for multiple metastases. It makes plans better in terms of reducing the normal tissue dose by reducing the leakage throughout these areas here. For each gantry position, the jaw comes closer to the field, the field edge, and minimizes the leakage dose.
So, now, let's talk about the automatic margin generation based on the distances from the isocenter as mentioned previously. As seen in this animation here, rotations have larger impact for targets that are further away from the isocenter. Institutions either use or intend to use different margins for the target's different distances from the isocenter.
It's extremely important to use minimum margins for these treatments because, as shown in this study, if you add one-millimeter margin and two-millimeter margin, you essentially double and triple the endpoints of V5, V8, and, V10, and V12. So, reducing margins improves that, using variable margins also improves that. The variable margin could be an important approach because only small percent of the targets are typically far away from the isocenter.
In this quick study, only 10 or 15% of the targets were more than 6cm away from the isocenter. So, there is no need to introduce larger margins for all of the other targets that are nearby the isocenter. I should mention that using larger margins can also impact the prescription dose if one follows the consensus guidelines. Depending on the clinical prescription strategy, about 10% or 15% of the targets that are at the sort of periphery of this decision-making lies may get lower prescriptions.
So, we intended to use variable margins at UCLA in the past, but for various reasons including the absence of the automatic generation tool that I just described, we decided to go with a uniform one-millimeter margin all around the targets. This was obviously an improvement compared to the two-millimeter margin we used to utilize, but if now we switch to variable margin of 0.5 and one millimeter, is going to be a further improvement. This variable margin option is now available in version 3.
One can define rules for margin generation that increases linearly in terms of distance, or it can be a step-wise approach similar to what I described previously. The targets that are closer than 6cm, for example, gets smaller margins and the targets that are further away get larger margins. I should mention that one can also have automated rules based on the volumes of the targets, and we can come up with many scenarios where you could use that rule based on the volumes.
So, in this presentation, I have quickly summarized the UCLA experience with the multiple brain metastases treatment with single isocenter, and I've reviewed the enhancements in Elements Multiple Brain Metastases SRS 3.0. I thank you for your attention.
Bogdan: Thank you very much for your lecture, Dr. Agazaryan, and thank you all for your participation. And please, enjoy the Virtual 2020 ASTRO.