The Use of SGRT in a High-Dose World

I work at Kelsey-Seybold, and today I’m going to talk about SRS and the use of SGRT with very high doses.

Welcome to Kelsey-Seybold. We have four radiation oncology clinical sites. We have five TrueBeams and one Edge spread across these sites. All of our sites use AlignRT, and we have four CT simulators. Three of our sites use the Solstice system for our SRS treatments, and one site uses the Encompass system. All of our sites treat SRS.

So what we’re going to talk about today is I want to discuss why SGRT is so important for today’s clinical treatments in general. We’ll look at the benefits of SGRT regarding SRS specifically. We’ll look at maybe some other ways to treat SRS and if there are pros and cons to those types of treatments. We’ll look at some trends across my four clinical sites specifically, looking at SRS versus IMRT versus WBRT, if there are any trends there. I want to look at a clinical study of a specific SRS plan and what that looks like. We’ll talk about some masks and ROIs, making the mask and drawing ROIs, and then maybe some obstacles that we ran into regarding our SRS treatments.

So why is this so important? So we’ve seen that in our clinical sites, we’re treating more and more SRS. And not just SRS, but high dose, a lot of hypofractionation, SBRT, SRS, higher doses in less fractions. And also specifically, we have had a very large growth in our number of facilities. We went from one site to four sites over three years. So we saw a very large increase in the number of patients we’re treating. And again, the higher doses with less treatments. And just the need for better patient monitoring when we’re treating such high doses on a daily basis. We want to make sure we’re doing so accurately every single day and doing justice to our patients and their treatments.

We also see that with SRS specifically, that we have unseen movement in closed face masks. I think we all know as therapists, you set up a patient in a mask and there is movement there, even if you can’t see it, and it’s very small. And when we’re regarding SRS, we don’t really have that luxury of movement at all because we’re treating within the millimeter.

So benefits of SGRT with SRS specifically. You have, again, that constant patient monitoring. Again, we don’t have a lot of room for error with SRS high dose specific treatments. A safer and more accurate treatment. Your patient feels better about the accuracy of their treatments when we’re treating something so small in such a vital part of the body. The therapists have a lot of confidence that they are accurately monitoring their patient through the entirety of that SRS treatment.

Reduction in mid-treatment imaging. I remember the first SRS I ever treated. We would use five-point closed face mask to try and reduce patient movement, and we would have to stop in the middle of treatment and do some mid-treatment imaging just to verify that there wasn’t any kind of millimeter or submillimeter movement during the treatment, and that takes time, especially if your physicists really like couch kicks, and then you got to take everything back to zero and re-image, and then you’re also moving your patient a lot more than necessary during those treatments, which can also cause additional movement.

And also, we have less table time for the patient because, again, you’re not having to take everything back to zero, re-image your patient, call the doctor back to the machine, check the image, move your patient. So your patient, especially in a closed face mask, you’re reducing their time on the table, and that benefits them and us on our treatment schedule as well. And again, that leads to opening up our schedule for additional treatments, especially if, like us, you’ve had a lot of growth, you have a lot of additional patients, new physicians coming in, bringing new clientele. You’re able to stay on schedule and still do justice to the other treatments on your schedule.

So I want to look at some other ways to treat SRS if you didn’t have SGRT or any kind of open face monitoring of your patients. So again, I started with five-point closed face mask, and you can treat it that way, but you’re losing your direct patient monitoring when you have that. So again, you’re looking at mid-treatment imaging to verify positioning, more time for your patient on the table, and I think probably about four out of five of my mask patients are all extremely claustrophobic. They’re very open about it when we show them what we’re going to do. They’re like, “I have claustrophobia,” and I’m like, that takes a lot of coaching and a lot of getting your patient comfortable with getting in that mask, especially on treatment day when the mask feels tighter. And for a lot of our patients, they need to be medicated. So just to help them relax, get in that mask. So again, if you’re using an open face with SGRT, you’re reducing a lot of that extra need for medication, and coaching them into that mask, take the mask off, give them a break, try and get them back in the mask.

BrainLab is another. We had BrainLab many, many years ago at our main campus site. We don’t use it anymore. But it’s expensive. And it’s this full dolophons on the Google. And your imaging dose is much higher because image, image, image. So you’re getting a lot of verification, but you’re getting a lot of imaging during treatment as well. You have Gamma Knife. We are clinical. We are not hospital. We don’t have access to Gamma Knife. But again, it could be a great way to treat. But it’s an all-day process, especially for your patient if they’re coming in for the surgery in the morning, getting the halo screwed in, they have to do the imaging, you have to create the plan. It’s a lot of time for your patient, and it’s a lot of time for your physician and your physicist as well, as they’re creating the plan, and it’s all done in one day.

And then you have—I’m so sorry, I’m losing my voice—you have SRS cones. But again, that’s an older style of treatment. It’s a little bit outdated. And your SRS cones have limited dose conformity because they’re perfect circles. You don’t get to have any motion as far as if you wanted to treat not in a perfect circle. You don’t get to do that with SRS cones versus using a TrueBeam with MLC abilities.

Oh, gosh. You all, I’m so proud of this chart. This took me so long to make. I deleted it and re-put it in there like four times, so this is the shining star of my presentation. So this chart here, statistics over five years with our one site to our four sites, as far as brain treatments in general. So that really nice—Do I have a laser pointer? I do. This nice line up top here, that’s total brain treatments, SRS, IMRT, WBRT, SRT, all of it. So again, we see a general increase in treatments in general. Oh my gosh. Thank you so much. If I start sounding like Mickey Mouse, just pretend you all are at Disney, okay? Thank you, Diana.

Okay. So that’s the general trend in brain treatments in general over five years at our sites. That nice blue in the middle here, that is SRS specific, and that is only SRS. That does not include SRT. That’s just our SRS. And so we see we have quite a large spike. 2023 is when we opened our second center, and that is one of our bigger centers. It’s got the two TrueBeams, and it’s also in a northern part of Houston, and it’s kind of our only center up in that direction. So we ended up having a large spike there and increase in treatments in general. And then that really nice green line at the bottom there, that is going to be IMRT, WBRT, SRT. So that’s everything else that’s not SRS. And then I have 2026 right here. So my little stars here, I’ll put those in myself. These little stars here, that’s where we’re at currently. Those are our accurate numbers to date up to April. And then these are projected numbers. And I can’t lie, I had a physicist help me with that math. We had to take averages, percentages. It was great. So these are projected numbers, and as you can see, we have an increase in general, but SRS really stays up there, where 2025 is a little different. And then we see here that even down here, we’re already treating more SRS than IMRT and WBRT, and even SRT.

So again, we saw generally we had a higher increase in brain treatments over five years. A lot of that is going to be due to, we just opened more centers. We had more patients. We hired more physicians. So we have more access to patients as we spread out over the Houston area. We had a consistent incline in SRS with a large jump there at the very beginning. And then we have that SRS is generally favored over IMRT and WBRT. If we can treat that one little spot in there, or even that four or five little spots in there and reduce dose to the rest of the brain, that’s what we would prefer to do. And I do have to admit that the statistical data I got from my physicist, she’s great, but it doesn’t differentiate between IMRT and 3D, just the SRS. So those numbers too, if we break those numbers down even more, the IMRT and the 3D, we would see that SRS is highly favored over either one of those modalities at our centers.

So one of my physicists was great. He let me invade on his very busy time, and I went and kind of interviewed him on the physics standpoint of SRS and planning and SGRT. So I sat down with him, and I was like, “What defines an SRS treatment?” Because I know me, that’s like one shot, high dose. But from a physics standpoint, what’s the criteria? How do we determine SRS versus IMRT or WBRT or even SRT? I asked him about margins and concentrated high dose. What does that look like? How much wiggle room do we have? And then I talked to him about over his career, that increase in SRS over WBRT specifically. How we went from, if our patient had two brain mets, you’re looking at the whole brain versus now we’re like, “Okay, well, we can just do SRS treatments ideally and spare the rest of the brain.” And then also too, just from a physics standpoint, how do they feel? How do you feel about SGRT and the monitoring, open face mask, those kinds of things?

So what makes SRS SRS? So single fraction and criteria at our facility, the tumor is no larger than two cm to be planned SRS. Our dose is typically 18 to 21 gray. Our margin is one millimeter PTV tolerance, and that is sup, inf, ant, post, right, left. So all six degrees. And then we can treat up to 13 isos. We have not treated that many, but about up to 13 isocenters, and then beyond that, you’re looking at probably a whole brain or an IMRT treatment. Our highest so far has been four isos, and every once in a while, if the tumors are close enough together, there’ll be two tumors, one iso, things like that. So far, ours has been four.

So again, what is physics looking at? What are they saying? So my physicist, been a physicist for about as long as I’ve been a lab, and he said, “The trending is we see”—I aged him a little bit, sorry—”a general increase in the SRS over whole brain versus IMRT.” Again, if we can spare the brain and we can treat one single high dose versus treating a large part of the brain with IMRT or a whole brain treatment, that’s what we want to see. But why? So SRS is favored over the whole brain for patient longevity. At the point that we’re treating whole brain, that’s the last option. We’re treating symptoms. We’re trying to get the patient comfortable, as they’re approaching probably end-of-life care. Whereas SRS, we’re looking at, we can treat that one spot, and the patient will be okay for—They’re not at end-of-life care yet. And then also SRS, favored over IMRT for those very sweet specific isodose lines. IMRT, you’re looking at a little bit of a bigger field. You’re not going to get as pinpoint as with SRS, especially with flattening filter free treatments.

So I asked my physicist, “What do you think about SRS, SGRT? How do you feel about it?” Our physicist hangs out with us for the entire SRS treatment, so he’s observed a lot of use. And my other physicist, she’s observed a lot of use with SGRT for SRS specifically. And the first thing he said was, “Patient monitoring is key.” We want to see any kind of movement because we only have one millimeter, and if your patient gets real comfortable, falls asleep, and they’re in a closed face mask, you’re not going to see that movement at all. Whereas with that constant patient monitoring, you can see that movement. If you’re like, “Hey, patient moved. We really need to re-image this,” you’ll see that within one millimeter.

Also, if you’re using beam control with those high doses, your machine’s going to turn off. It’s going to be like, “No, bruh. You can’t treat this.” So again, not only are you monitoring your patient, SGRT, and for us, AlignRT is monitoring the patient too, and if it sees anything past that one millimeter in any direction or that one degree, half a degree, whatever you pick in any direction, it’s automatically going to turn your machine off, and it’s not going to let you treat again until you verify that your patient hasn’t moved or if they have moved, that you’re readjusting your patient back to iso center.

Also too, we have a decrease in that mid treatment imaging, where we don’t have to verify just because we can’t see. If we’re re-imaging, it’s because our system has noticed movement, again, past that one millimeter, and it’s time to re-image to verify the patient. So we’re not just moving the patient back to zero with those sweet couch kicks or anything like that. If we’re re-imaging, it’s because it’s necessary, not because it’s verification. Which also decreases time for your patient on the table inside that mask and on top of that comfortable tabletop there.

So this is a specific SRS plan that we treated. This patient is a 61-year-old male, stage four melanoma, metastatic to the brain, and according to consult note from the physician, the recommended SRS total to 20 Gray in one fraction. If you all can even see it, that tiny little guy right there that we treated.

So this is MR. The MRI revealed a five millimeter lesion in the right superior gyrus, and we did indeed treat that 20 Gray in one fraction. Our energy was 6XFFF. And I actually got out a ruler and measured, it really was five millimeters. So I was like, “Is it really five millimeter?” Yes, it was.

I personally really like this image because it helped me visualize the dose and the dose fall off that we get with SRS and with the FFF type energies. So we have here… That’s not right. Sorry. There we go. So we have here our PTV, which was again, where the 2,000 centigray is going. That’s that really nice yellow color that we get right there. The blue is very quick dose fall off. That blue right there is about 271 centigray. So that part of the brain is getting less than a single whole brain treatment. So, for me, this helped me visualize again how rapidly the dose falls off, which emphasizes, again, no wiggle room there. You’re treating a very high dose to a very small part of the brain, and that dose falls off fast. It’s very pinpoint.

So monitoring during treatment, our SRS protocol with SGRT is one millimeter, so it’s going to monitor that one millimeter or that one degree. During treatment, our deltas went out of tolerance, and we were like, “Okay, well, it’s not going to let us treat.” So we need to take our second CBCT on the… You all’s right. That is our initial CBCT shifts. So our first image of the patient, those were the shifts that we had. We apply the shifts, we take our SGRT, and then we begin treatment. So I wanted to emphasize that if you see on y’all’s left here, that negative 0.11 was what we got when we had to re-image. So that is 0.01 out of tolerance that the machine and SGRT said, “No, you need to re-image.” So even 0.01 out of tolerance, we re-imaged the machine, the SGRT, Vision RT saw that movement in the patient, and we re-imaged. So, it works. We saw it right there. Everything else was within tolerance. It was just that 0.01 out that it saw.

So this is not my patient, this is my coworker. So making a mask. So a great plan is going to start with CT and how we make our mask, how we align our patient. That’s also going to really determine our ROI for treatment. So when we’re making a mask in CT, again, we use the Ulta system. So we’re looking at going under the nose for the mask, and we want at least two fingers above the forehead of the eyebrows. My coworker kind of has a big head, so we have a little bit more than that. But again, you’re looking at under the nose, we want the whole nose and a decent amount of the forehead so that there’s enough surface area for your cameras to actually monitor.

Looking at laterally, when we’re making our mask laterally, we want to go down to at least the hairline or the ears. So even constructive criticism of the mask we made on him, we could have in—Right there, we could have actually made our mask a little bit lower to have more surface area if we were actually going to treat him, which thank goodness we were not. So even just our own constructive criticism, our mask could have been a little bit better for a little bit more of that ROI surface.

So this is the ROI we used for our actual patient. As you can see, we include as much as we can without drawing on the mask itself. So, a couple of things. We want to try and draw as much of the nose as we can, but if you have a patient that really likes to flare their nostrils, just cut those mama jamas out. Same thing with the eyes. We like to tell our patients, “Please keep your eyes closed during treatment. Don’t open them, don’t blink, just close your eyes.” If you have a patient that really struggles with that, again, you can crop out the eyes. If they’re blinking quite a bit or if they kind of have those shaky eyelids, you can take those out. But ideally, the more surface area, the better. So our protocol is we tell our patients, “Please close your eyes.”

So we had some obstacles. Again, I don’t think you can really treat SRS without three, four, or five couch kicks, at least not at my center. And so ideally, when you’re moving your couch and you’re rotating, and your gantry is rotating during treatment, chances are you’re going to block a camera somewhere because your patient’s not staying at zero. And so I actually contacted Diana and I was like, “Listen, you got to help me out. We’re having a lot of couch kick issues.” And she was like, “Well, send me pictures of your ROI.” And I was like, “Done.” And she looked at the pictures and she said, “I see your problem. It’s with your ROI.” So she reminded us very graciously that you need more surface area because if you’re blocking one of your cameras, there has to be enough surface area for the other two cameras to see enough to keep treating, or else you’re going to see either false movement or you’re going to block too much and it’s not going to see anything. So it all goes back to, again, how you’re making your mask and how you’re drawing your ROIs. There’s not enough surface area, you’re going to have issues when you’re kicking those couches and rotating your gantry.

So conclusion, as we see a growing case of SRS treatments, especially in my facility specifically is what we looked at today, that increases the need for SGRT for patient monitoring, especially if you’re treating a lot of SRS, SBRT. That can take a lot of time up on your schedule. We want to do justice to our patients, but we want to realize too that there are a lot of people waiting to be treated. When we have smaller margins and higher doses, very small room for error. So with that constant monitoring of the patient with things like beam control, we are able to treat those higher doses very confidently as therapists, as physicists, as MDs.

And so with these two things combined with everything that we saw today, I think this leads to a greater need for accurate patient monitoring. We’re seeing a lot of hypofractionation. Again, SBRT, SRS, SRT. If you can treat a higher dose in a smaller margin, spare more of the body, spare more of your patient needing to take FMLA for nine weeks when they can do it in four weeks. Ideally, we want to do that for them and it’s more accurate. We’re sparing a lot more of the tissue. And so I think we see this need for SGRT and the patient monitoring as technology grows and as we treat more and more in higher doses. Thank you.

 

 

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