 Thank you. It's great to be here. I know we're a little late, so I may skip a few slides here. If you have any, if you want the slides, you can send me an email or something. I can send them to you. I'm going to talk today about quality assurance, mainly about simulators and ancillary equipment other than the linear accelerator or the the radiation device. And yes, I'm from North, I live in North Carolina. I used to, I grew up in Washington State. That's kind of, if you look at the United States, it's one side and the other. So I'm far from my family where I live now, but it's, it's in the kind of the southeast corner. I was in Mexico for two years, which is a lot of fun and and but those are the only two languages I know, so you're safe if you're speaking anything else other than those two. So there's a couple of topics we'll go over today. Some radio, radiographic simulators, CT simulators, and then the imaging that goes with the mega-voltage linear accelerator and the KV imaging, the MV imaging and patient support systems and then immobilization devices. So this is a picture of a conventional accelerator or simulator here. It looks a little bit like a linear accelerator. It's not, but it's meant to look like that because it's meant to simulate a treatment. So you have an x-ray source that that is used to image and this has an adjustable collimation so that you can set up your fields. And it has, and this particular unit here, you can adjust your source to access distance to match different machines. So you can have it at 80 cm or you can have it at 100 cm to match different machines. And then you have the patient support assembly where the patient lies. You have a rotating gantry to set up different angles. You have the imager and this also can be adjusted closer and farther from the source. And a field light for setting up and marking those fields on the patient. And then not shown in the picture is a laser system to localize where the isocenter, where to set up the patient and marking those as well. Here's a newer simulator, but it's basically very similar. It has the same sort of things as before. So you have the support assembly, the x-ray source with the collimation, the gantry that rotates. This version here does not have an adjustable x-ray distance to the isocenter, but I have some mode to simulate in 80 cm, even though the source only stays at 100. There's a field light as well and then the localizing laser as well. And so basically this is the same design as before. It hasn't changed much. It's the same purpose as before. Although this one does have a comb beam imaging capability so you can image as well. So some of the main components there that are important is the imaging source and the detector. The lasers also an optical, I didn't mark that before on the last slide, but there's an optical distance indicator where you can see how far the patient's surface is to that source and then you can use that to match as well. The field light and the patient's support assembly. So the purpose of a simulator is to reproduce the geometric conditions of the radiation therapy equipment. And this should basically we keep this at the same sort of when we go to do the quality assurance on this, we use the same mechanical quality assurances that we would use for our treatment machine since it has a very similar purpose. And then the image for that's that's for the mechanical checks. And then for the image quality, those are checks similar to diagnostic radiology. And so there's a report, the APM has a report on this that this is for this is a general report for radiation oncology, but it does have a little bit in there for for simulators. And then this is a table showing a lot of their recommendations for tolerances. We had a discussion earlier about tolerances and how that should maybe be defined as an action level and what level would you adjust things? But this is their recommendations. And so these are basically the same that are recommended for the linear accelerator as well, only it's mostly just the mechanical side of that. And so there's different things there that that we that that you look at as far as like the indicators for the for for the different field size and the gantry and the collimator and so on and so forth, as well as some image quality and diagnostic and diagnostic stuff as well. This is a CT simulator. So this is very this is kind of the newer generation for 3D planning. And so now instead of setting the patient up with an x-ray source where you can image a 2D image of your fields, we take a 3D image. So some of the components here, there's a control room to control the CT. The CT bore, there are internal CT lasers that that are used to image where the center of that CT is. There's also the patient support table where the table where the patient goes. And then there's often there are these external lasers that are usually about 50 centimeters from the internal lasers. And that's used to set the patient up and to mark the patient to mark an origin outside of the CT and then CT contrast injector. And then also you can see here, this is a water bath for putting in thermoplastic material to set up the patient and to immobilize the patient. So once the patient is brought in, there's basically the CT simulation has three different aspects that happen. The first is at this inside this simulator room, there's the CT scan. And that's similar to the diagnostic CT with the added requirements of the localization and the lasers and the imaging and setting that patient up as you would for an actual treatment. And then the treatment planning and the CT and the actual planning on that CT that happens in the planning system. And then at the machine, before treatment, the patient is set up based on the instructions that come from the prior two steps. So at the CT, the first patients align in the treatment position and then you immobilize them. This is showing a mask immobilization system. Mark the origin. So this is basically marking the lasers, positions. And that's the location of the lasers during the CT and the CT image is acquired. And then additionally, it's also possible to, in some cases, to mark the isocenter in the CT room. We actually don't do that often. You can, the alternative would be to set the isocenter during planning and give instructions at the treatment as to where the isocenter should be. And then the patient set up instructions are recorded as well. So here's some examples of different setups you can see here. These are images that were actually taken and put into a document for the treatment machine saying, here's how we set up with this, you know, different instructions for, first off, marking where the lasers should be and also any details about which devices are being used for the immobilization if we're using a certain wedge or a certain cushion under the head or so on and so forth. So components of the CT simulator that we've talked about before. We're going to go over all of these and the quality assurance for those. And here's a few of the reports that the APM gives that deal with CT simulators as well and report 83. There's the main one that I'm going to go over a little bit from. So some of the recommended quality assurance that goes into this. Initially, there's the radiation safety survey that goes with the installation of the CT dosimetry measurements for dose, the alignment of the lasers, the tabletop indexing and position of the tabletop and alignment with the imaging plane, the gantry tilt accuracy and the scan localization, CT dosimetry, so on and so forth. So the lasers, once again, there's the internal lasers. There's some mounted on the wall that are typically 50 centimeters from the internal lasers. And then there's also an overhead laser that goes with this set of external lasers. So some of the things that are verified in the quality assurance there is the gantry lasers should accurately identify the scanning plane. So when you set up to that, that low set of lasers and you image that should be the same plane and they should be parallel and orthogonal to the scan plane and intersect the center. The external lasers should be accurately spaced from the imaging plane, so that 50 centimeters should be verified when you tell there's the table has an indexing system and you can tell it to go 50 centimeters in. It should go from the external to the internal. And then those should also be parallel and orthogonal to the scan plane. So here's a QA device that this is one from a report. It's an optional one that is used to verify some of these things. You can see here there's some markers here that and you align this to the lasers and then after that you do a CT scan of this and you look in the axial scan and you should be able to see some markers within here lining up and if they if they line up, then you know you're within a certain tolerance. And if they do not, you know that the lasers may need to be adjusted. And you can also use this if you have some set distances that you can verify the measurement in the CT plane. Here's the one that we use. It's it's similar concept where you have some markings for setting up to the lasers, you set up to the lasers, you take a CT scan, you should be able in that slice, you should be able to note, notice where those marks are and that you're aligned with where you expect to be. So often these external lasers, if they're there, they have the option of being adjusted so that you can tell them I want to mark the isocenter at this coordinate and you can be able to move the lasers to that coordinate and then mark that position. So if that's an option, it's important to verify that that motion is linear, it's accurate and it's reproducible. The tabletop there often are special tabletops that are designed for radiotherapy. And if and if so, those can also be installed on the CT simulator. Some of the functions of those, one of them is that it can register immobilization devices. So here you can see this bar is used and it has some perturbances here that you can use to set up an immobilization device on and index it to that table. So it's laterally it's going to be in the same position every time and longitudinally as well. So some of the criteria for a tabletop is that it should mimic the treatment table. For this reason, often we want something that's a flat surface, flat level orthogonal, it should have similar sag properties. So you're not too much, if you put a heavy object on there and you extend it, you shouldn't be sagging too much. And then the motion indicators in the table position should be accurate and reproducible. So some basic quality assurance here is just measuring, is it level and is the, if you put something there to measure and then you move to a certain index, is that are you moving the distance that you expect to? This is a very simple test that you can do to verify this normal CT for CT simulation. Many of the gantries can be tilted for diagnostic scans. So there's actually a button that will tilt the bore back and forth. So often for a diagnostic purpose they may not look too carefully at what that's set at. So it can be important to make sure that when it goes back to zero that it is at zero and maybe that it's marked as to where that level gantry is for a radiotherapy scan to make sure that there is no tilt for those scans. Also the CTs, they are often set up with a scout scan. So you take a radiograph, basically the patient is aligned and then moved in and out and there's a 2D image that's taken and then you use this to mark where your start and end of your scan should be. So one recommendation is to verify that where you ask for the scan is where you actually get the scan. Another thing is the radiation profile. So this evaluates the pre-patient collimation and so there's some reasons why this should be accurate. And so that you're not either overdosing the patient or you have too few of increased, you have too much quantum noise due to too narrow of a profile. So the way that you measure this one is with an exposed film basically looking at your profile and then comparing that to what you expect. The other one that goes along with that is a sensitivity profile. So when you take a scan, you have a slice thickness for that scan and if you have some sort of a diagonal wire in a phantom, you can use this and you can see on your axial slice the thickness of this or the length of that wire, you can use geometry to determine how thick that axial slice was. So even though this image may look very similar for two different slice thicknesses, the length of this line which is a diagonal wire through that phantom will change based on your thickness of the scan. So dose, often dose for CT is specified in what's called CTDI. And so this is a lot of equations here. Basically what you're doing is with CT you have a high dose in the center and there's this long profile. So you measure dose along with a very long ion chamber and then that's basically the integrated dose over that entire profile. And then you use some equations to calculate what dose you would get for multiple slices. So for example here for an axial scan we use CTDI volume which in is the number of simultaneous axial scans per slice. T is the thickness of one axial scan and I is the table increment. So this is how you would go about calculating from your measurement for one slice. And here's a picture of a CTDI phantom. There's a body phantom and a head phantom. Here you can see here's the head phantom, it's smaller and basically you measure dose at the center and you measure dose at the edge. And you can see here there's this long hole for the ion chamber. It's actually a very long ion chamber that goes in there and measures it over a long length. And here's the similar one for the body. The CTDI 100, that's basically the 100 there means 100 millimeters, that's the length over which it's measured. And then here's your absolute dose. You get that from temperature pressure correction, you have your raw reading, temperature pressure correction, electroner correction, chamber exposure, calibration factor. So this is what you would get from a dosimetry lab for your chamber. And then a conversion to converts exposure in there to absorb dose in medium. And so that's how you would get into a dose in centigrade. Some other tests that are recommended are the generator tests. So for example, this is actually set up with a, not with a CT, but with a, anyways, with the KV onboard imager. But you can, there's lots of detectors you can use to measure some of these other things like peak potential and half value layer and some of the quality measurements for your X-ray source. And then here's, I'm not gonna go over this too much. This is just some of the recommended frequency intolerance for those tests. And then so what we talked about before was basically the mechanical tests and the dose. There's also some recommendations for image quality and for looking at that, these include the accuracy of the CT numbers, which is quite important for radiation ecology because we're using those numbers for our dose calculation. There's also image noise, in-plane spatial integrity, field uniformity, electron density to CT conversion, CT number conversion, spatial resolution and contrast resolution. So this is a typical phantom. This is a cat fan phantom and it has different inserts and they each test different aspects of this. So for example, this one here, you can see these different larger circles. Those are all different known Houndsfield units or densities. And so when you take a CT scan, you can measure the Houndsfield units and you have the density and you can verify that what you see is what you expect. Here, you can see here also, this has the diagonal wires for looking at the sensitivity, the actual length of that CT slice. Here's a low contrast resolution. This is a good test to do. When you first get it, you do a baseline and then you would basically measure over time. Am I able to see the same number of these low contrast inserts as I was at baseline? Uniformity and noise. So there's some corrections that go into correcting beam hardening, so on and so forth to give a uniform scan. So you can look at that and for example, this one here has just basically a uniform density and so you look at, am I seeing any beam hardening? Am I seeing a cupping artifact where the Houndsfield units in the center are different than at the edge of this uniform area? And then also if I just look at the noise, is it similar to a baseline? And then finally, high contrast resolution. Here you've got some high contrast inserts that are closer and closer spaced and so you look and see when I look up to this up close, am I seeing which one can I resolve and so you take a baseline and you basically measure that over time. And so here's again some recommendations for how often those should be done. All right, so MV image guidance. So here we have a linear accelerator. This is two different designs and both of these have a portal imager. Basically we're using the radiation source itself from the linear accelerator to image and so this is two different vendors but they have similar designs. They're basically using a flat panel for that. So here's an example from the planning system from our CT. This is what's called a digitally reconstructed radiograph where you basically reconstruct what a 2D projection should be and then you can measure with the MV portal imager when you get a projection through that patient and then you can use these two to match and see how well your setup is for a certain case. Okay, I'm just gonna skip that slide for a second. So in addition to two dimensional there's also some cases with three dimensional imaging with megavoltures. So basically you're measuring different projections as you go around and then you do a tomographic reconstruction and this is the tomotherapy MV CT. You can compare that to the diagnostic CT and so this is an option that exists in some with some technologies and here's another slice through there and so the dose for these are in the order of five to 15 centigrade and so the image quality may not be as good for these but for setup it may be useful. You can get a three dimensional image just using your megavoltage source. KV image guidance is usually mounted orthogonal to your linear accelerator, so at 90 degrees and so you have an imager and you have a KV source mounted and it rotates around the gantry as well. Here's an example, this is at Beaumont Hospital and which was, this was the first one that was built by some of the guys I know and I heard a story about this that the physicist who was designing this is Dr. Jaffrey and he told the main, he had this bench top system and that he was dealing with and he told the main physician, he said, you know, I think we're ready to go ahead and work on putting one in the clinic and so the doctor said, okay, and then the doctor came in on the weekend and he heard some drilling and he came in and they had this huge drill, the physicists were just drilling through this wall here. He said, what are you doing? We have to treat on Monday and said, oh, we'll be ready. So they just kind of did it, often did it. So you have basically a KV source and a flat panel imager and they're mounted orthogonally and oh, there they are. You can see that they are putting it in. So when you get an image there that's basically, you know, it's KV, it's around two centigrade and it can get a pretty good image quality for an onboard imaging system. And in practice, the way this works is there's a, you have your planning CT and then the day of your treatment you'll have a comb beam CT, KV combing CT and then there's a registration of those to verify that the patient is set up correctly. And there's a lot of different recommendations for these. So I just put a bunch of them up here. We'll go over some of that. Some of the corrections that go into a KV system, one of them is that you have these two different coordinates where your KV system is mounted orthogonally and there's a correction that goes into looking at when, the coincidence of those. So basically here's a setup calibrating this where you have some BB, something that's very small and that you can high contrast and it's imaged both with the, it's set up to the megavoltage isocenter and then image with the KV source and the flat panel. And as the gantry goes around, this varies in position and so you get some sort of a, in both axes you get some sort of a synograph in one axis and the other axis you would get some sort of a difference there and this is called a flex map correction where you measure this and then correct that back to the projection images so that the isocenter is placed on your two dimensional images correctly each time. And here's an example of, from a paper that shows different flexing in one axis for different machines. So you can see here, they have all these different machines and so you can measure that and then you correct it back and here's their correction back. So this is the absolute flex that they measured and then they're residual. And so then you can do a daily check happens to make sure that when you set up to your radiation isocenter based on the lasers that your position of some marker is at your isocenter and that this is not changed drastically. Some other details for the imager. You have a lot of corrections that go into it. This is a schematic of that and there's a dark field that happens and then a flood field. So basically you have two different corrections and this often, if you see a difference in image quality one of these may have to be re-measured where you have basically a dark field is where you're measuring the output from this flat panel with no radiation and then the flood field is with the full radiation afterwards. For 3D CVCT often there is different modes that this happens in. And here you can see this is a normal mode where you have your imager, your patient set up at isocenter and your source. Often this imager can be shifted so it doesn't measure the full patient but it allows for a much larger field of view to be measured. Also in addition there's some filters, what's that? Filters, yes, so this is what's called a bowtie filter and basically what this does is because your patient, as the X-ray source goes through the patient you'll have some areas that receive a lot of dose on the edge because they're not being attenuated very much. And so when you get to the panel your area if you have just the raw source will have low fluence in the center and high fluence on the edge. And you can normalize that by putting this filter in ahead of time so that you have high fluence before the patient in the center and then when you get to the detector it's all more or less normalized. But this also requires having a correction for this and including in the projection space for the difference in fluence. So for example with the flood field it needs to account for these type of filters that go into place. So some of the routine QA for these 2D and 3D imaging there's collision interlocks making sure they work, positioning, repositioning tests, treatment and imaging coordinate coincidence, scaling, spatial resolution, contrast, image uniformity, dose, beam quality, so on and so forth. So similar to the other cube phantom we saw before there's some basic tests that can go into this at certain frequencies depending on how often you decide that that needs to happen where you align something to the isocenter and then either shift it and see if that shift is what you expect or at the very least measuring to make sure that the isocenters are coincident. And there's other devices that can be done to look at scaling to make sure that the distances are correct and so on and so forth. And here's an example for 2D looking at the scaling and then 3D as well where you know the distance between two different objects in a phantom and then you just measure that in the imaging as well. So also contrast spatial resolution. So we looked at that for the CT simulator there's also phantoms that can do this for the 2D imaging. This is one for KV or inside here you have these different, this is for high contrast resolution or spatial resolution here's your contrast resolution and basically you measure a baseline and then you see how do you compare to that. And one thing to note here is that your detector has certain panel resolution and if you rotate this phantom it should be basically the same each time because your spatial resolution will depend on the orientation. Uniformity you can measure to see whether those dark field flood field need to be re-measured and then for the 3D KV imaging basically a lot of the same imaging tests that happened for the CT simulator you can do these for a comb beam imaging system as well. For example, here's the diagnostic CT slice for this part of the phantom and here it is for the comb beam. You can see these numbers here are relative because there's a lot of scatter, that extra scatter that reaches the detector whereas we can expect these numbers to be pretty consistent and pretty accurate. So often there's a calibration that happens where you actually measure these howling field units of these different inserts and then you have a calibration to match what you expect for those. One thing to note that accurate CT numbers in a phantom like this especially if this is the phantom where you're doing the calibration for a comb beam that may not translate to accurate CT numbers in the patient. So the CT numbers for these comb beam systems are often relative and we don't expect them to be nearly as accurate as a normal diagnostic CT. And here's the same thing for the high contrast resolution and this will be dependent on the imaging protocol. And then here's the inserts for the low contrast and the uniformity and the noise. So for MV imaging, often the dose is, we're using the same imaging, the imaging is done with the same beam quality as the planning system. So it can be just directly translated if you're using a certain number of monitor units you can use the planning system to calculate dose. The exception would be for some linear accelerators they use a lower energy to get a better contrast resolution. For KV imaging, here's a setup showing a device measuring the dose for a KV system. And so there's lots of meters that are able to measure dose, KVP, half value layer, a lot of these beam quality indicators. For 3D, for your comb beam dose you have a large, it's not a collimated KV source and so this is done with a farmer chamber in a cylindrical phantom. And then here's a couple of recommendations that exist for how often a lot of these tests should be done. Basically for the daily, what's recommended is just verifying geometry that you can shift accurately and also that everything's functional, your collision checks are functional. These are things that have to happen on a daily basis because these imaging systems that are on the linear accelerator, we're not really using them for image quality as much as we're using them for setting the patient up and for repositioning the patient. So that's the most important aspects. And for monthly, basically what's recommended is geometry and then some image quality baselines as well. And then for annual QA, that's when they, what's recommended to add in as well like beam quality tests and imaging dose. All right, so moving on to patient support systems. So these have two aspects, one's geometric, one's dosimetric. So what we care the most about is that these accurately index position because we do a lot of shifting where we have some instructions that the patient was set up at this point, these marks, and then we want you to shift the isocenter by a certain amount, so on and so forth. So accuracy of the table index, patient repositioning, the couch angle, and if there's, some tables, fancy tables have six degree where they're able to measure pitch and roll. And so obviously those would be included as well. And then dosimetric, the skin dose, so the table can increase the skin dose and reduce the tumor dose due to the fact that there's added scatter at the surface where the skin meets the table and then there's attenuation overall when you get deep into the patient. And then an altered dose distribution. So here are some examples of a lot of different couches and these will often have an associated weight limit. So it's important just to know what that is and have that accessible so that if a large patient comes in, you know what that limit is before you put a patient on the table. So here's looking at the increased or the effect of the couch on the dose. You can, these plots here are the open beam and then up here these ones with the open circles are the beam going through the table. And you can see there's an increase in surface dose due to the scatter and then later on there is a slight attenuation at deeper depth. So this is the depth within the patient and this is the percent depth dose. So increased surface dose and decreased dose deep within the patient. So looking at attenuation, here's some measurements of different tables and as you change your gantry angle basically you've got a gantry, if you've got your, here 180 is a beam coming up through the table directly and then this is kind of an oblique beam that's going through the table at an angle. So you can see there's gonna be more attenuation as you go through obliquely and a nominal amount going through, just straight through the table. And some of these, the attenuation can be pretty high. This table here has a foam core. So there's a carbon fiber table but it's got a foam core inside of it. So you can get up to 7% attenuation at an oblique angle. So one way to manage this is to include this inside the planning system. Here's some models of ARIA where you can actually choose which table you're using. It has a couple, it doesn't have all of them but it has a couple of them there and so it actually puts the geometry in and you choose to place it centered under your patient where your CT table was and then you can assign the household units for these and then you can, if you know which household units to use or you can make some measurements, some dosimetry measurements of your table and decide which household units should be used to get the correct attenuation. And the good thing about this is that this, instead of having a single number for your attenuation, you can have different gantry angles and it will account for that geometry for your different. Whatever your geometry is for your beam and for your table, you can account for that. And so that's one way to manage it. The other one would be to use some sort of a hand transmission factor or if the attenuation, if you find that that table has very little then maybe just do nothing about it. Another thing to mention about treatment tables, often there are these support systems. They have these bars that are very high attenuative. And so just knowing if your table has those, often you have to give some instructions to move those out of the way for certain beams as opposed to treating through them. So immobilization devices. So these can account for these have some attenuation properties, dosimetric properties as well. And so you can account for those within the planning system or using some manual number as to how much it attenuates. And so often these are included in the CT so you don't actually have to do anything because they were at the CT, these were included. Here's the table of some of the bars where you have a different types of both trays that go in the Linak head and then also some things that go with the patient. And so if we were doing a two dimensional measurement we can just use one of these values here and account for it there. If it was a 3D treatment case then we would include it in the CT and we wouldn't apply this value. And then here's just an example showing some of these devices are very complicated. They have different inserts. So this attenuation can be different for different geometries as well. And others, for example, here is a frame that goes around the patient. And often if this is the case we may just want to, the easiest solution is just to avoid going through some of those areas. All right, so that's what I have for today. Thank you. Thank you.