 All right, good morning again. So today's my last day here. So we'll go out with a bang. Today, we're going to talk about MRT, basically, about commissioning and how do you go about when you first set up this technology, all the tests that need to go into preparing for using this. So here's a basic summary of the things that go into that. First off, there's two different aspects for commissioning. The first is the delivery system. So that's the linear accelerator and all the aspects for that. So there's the mechanical tests, the dosimetric tasks, and then some that are IMRT specific. So first off, there's the ones that, just for 3D in general, those are all basic requirements that have to be done prior to specific ones for IMRT. And then for the treatment planning system, similarly, there's all the same tests that you have to do for commissioning a treatment planning system for 3D. And then in addition, there are some other things for IMRT. And also listed here are a few references involved for those. And then in addition, there's just some dosimetric verification for different types of plans. So if you're going to be treating certain types, head and necks versus different types of sites and types of plans, just a verification per site, and then any type of independent verification and just setting up a system for pretreatment verification. So here's all the steps that go into this commissioning. So all of these first ones, these are all performed initially. And this should be prepared as commissioning and then it's done kind of per plan as well. So this is from Estro, the Estro guideline booklet. And this is the suggested layers of quality assurance. So here on the bottom is kind of the very basic ones for the machine, dosimetric and geometric characteristics. And then as you build up, you get more and more comprehensive measurements. And what they suggest doing is when you're doing your initial commissioning, you start from the bottom and you work up. So you start with the basic measurements, you're verifying your output, just the basics. And then you build up until you, and once you're sure that that is correct, then you go to the next one and so on and so forth and building up. So once you've already done all the commissioning and you're going to do a new technique, then they suggest starting from the top and going down. So you verify this first. And if that looks great, then you may be just fine. And then working down from there, if you have, for some reason, there's something that's not matching up, then you work down and see where your problem is. All right, so delivery system and commissioning that the delivery system for MRT. So there's a couple of different tests that are suggested to do for these. They include a picket fence test, which we'll talk about in a second. Basically looking at MLC, the accuracy of the positioning of that, verifying the performance for small numbers of monitor units. Because often if you're delivering, especially for a step and shoot, you have very few monitor units for these fields instead of one large field with a lot of monitor units. MLC control issues, data transfer, fidelity. MLC physical characteristics, so looking at the leaf gap and very carefully looking at how your treatment planning system is modeling this, how the delivery system is defining this, and making sure that those match up. And any additional issues for sliding window MRT? So is your leaf speed and leaf position is that being controlled accurately on the machine? And is there a minimum leaf distance that has to be defined for the machine to make sure that there's no collisions? All right, so the first one on that list was MLC position accuracy. So just a little bit about that. So for a 3D case, the MLC typically defines your field edge. So it's out there on this penumbra region. It's usually not an area that we care too much about the dose. We're outside of the volume. We have some sort of a dosimetric margin. So it may be that for a 3D, it doesn't have to be too accurate. It needs to be accurate, but it's less consequential if there's an error with those MLC positions. However, for MRT, since we have all these multiple small segments, and if we're often we have these leaves sweeping across the field, so those leaf edges are actually at some point there within your field. So you have there defining the dose to the target and not just to the periphery. For that reason, the MLC positions are more important to be accurate for MRT than they are for 3D. And so when you have these rounded leaf edges, so you may have a difference between where the light field is and where the radiation field is. Or you have some sort of a penumbra for that. And so these are all things to take into account. So some tests that this is one that's proposed by AAPM, one of the task group reports, to look at this and is to first measure the difference between the light field and the radiation field. Once you know that difference, you can account for that and then create a set of test sequence that abuts those fields at different areas within the field and then take either a film or some way with two dimensionally verifying that dose. So here is, and then they also suggest repeating this at different gantry angles because you have the gravity in different areas and just seeing how that affects it. And also often, for example, there's this carriage where the MLC will move from different positions. So they also suggest repeating this for different carriages. This is an example from that report showing this. So basically you've got these abutting leaves in different areas in an attempt to get a uniform dose. So you know what the radiation dose profile is. You know where the MLC position is. You've lined them up to get a uniform dose and then you create this field where you're trying to create a uniform dose with different abutting areas. So in this report, they suggest that this detectability should be, for this test, is around 0.2 millimeters and the accuracy at these edges here. The uniformity should be around 5%. Similar test but also slightly different is the picket fence or garden fence or it has a couple of different names. Basically in this test, you create a test sequence that has a defined gap like 1 millimeter and it's at regular intervals and then you irradiate it. You get some image either with the portal imager or with the film and then you look at those and you know where your positions of those leaves should be and they're well-defined because you have this gap and then you should be able to detect an error that's around a half millimeter using this. And then this can also be repeated at different gantry angles. So here's an example of this. So we have this kind of nice straight lines going down. We can see we've defined these positions of the leaves. One millimeter gap and when we move, we irradiate it so on and so forth. And so this shows that as we look down this line, if there's an error, if one of these leaves are off, it should be fairly obvious. And there's other ways you could kind of write some code to analyze this numerically or also just a visual inspection at the very least. You should be able to tell if there's a problem with one of those leaves. And here's another example of this from a paper. So here you can see if you just take a profile across, you can see the positions where these gaps are. And the benefit of having multiple gaps here is that often when you go to commission the MLCs, you have a couple of different variables there. Often you define the positions or it's somewhat like the jaw calibration. You want to make sure that this is linear and that the distance is the same between those as well. All right, so small monitor units. This is a figure from a long time ago looking at some old machines, just showing that there is in some cases this kind of, if you get smaller number of monitor units, you may not be delivering. There may be like a few percent difference either over-response or under-response that it's delivering either more or less than you expect. So just a verification of this by delivering smaller number of monitor units and checking to see is the output linear with number of monitor units for small MU. And they also verify, in addition to output, looking at flatness and symmetry and making sure your fields are flat and symmetric for those as well. So the other thing is that there's this, with IMRT you have more variables for your plan. You're not just defining one set of MLC positions, one set of jaw positions and gantry, things that you can all verify in the record and verify system. So you have the treatment planning system, it sends all these things to the machine and there's a lot there to verify. In fact, you can't really verify everything because now you have multiple segments all for the same field. So it's really a different format in some ways than a 3D plan where you just have a single set of parameters for those MLCs. So, and also in addition to that, there's lots of details that are machine specific, like how those MLCs are calibrated and how is that in those plans, how is that indexed to the number of monitor units, the MLC position as you go along? How is it measured by the machine? And all of these details are good things to know for your specific technology. How is it handling this? Some machines require that you manually do the MLC calibration, whereas other ones, they have some sort of automatic process for that. And it's important to know those details, is there a secondary measurement for the MLCs so that you know if there's an error, kind of where to look for that and where that may be coming from. Also, how to recover from delivery interruptions. Now, instead of having just a static set of MLCs where you're just delivering a certain number of monitor units and if there's an interruption, you can just deliver the rest of those. Now you have this motion across and how does the machine handle that? Are you able to start in the middle of your treatment, of your field and deliver the rest and so on and so forth. So just another note, IMRT different vendors have different ways of dealing with this. And this is kind of an older note. I think probably they're much more similar now, but at least in the olden days, some of them was IMRT was basically an extension of 3D where each field is, each segment is kind of treated as a separate field or is there an MLC control system where each field has this shape and MLC sequence that goes with it. So the other thing with the data transfer is that you can verify with 3D basically all of your variables because they're all there in front of you and it's a little more difficult for IMRT because you have this sweeping motion across and this MLC motion. So there's some dosimetric measurements that you can make that can be a good surrogate for that, but it's something to think about as far as when you go to verify treatments at each fraction. And so at commissioning, it's a good idea to have some sort of a policy in place on how are you gonna go about verifying the record and verify the transfer of the plan from the treatment planning system to the linear accelerator on a per plan basis. So MLC leakage, so leakage is also something that's more critical for IMRT than for 3D. And that's because this MLCs, as they're sweeping across a lot of those monitor units, the shadow of those MLCs is in the treatment field. And so that leakage becomes a little more important. Also the leaf penumbra, some machines have this rounded leaf edges and some may have these focused leaves, so on and so forth. So that penumbra, it's important to know how is that, what's the shape of that? And this needs to be measured with a high resolution detector, something that's able to measure that penumbra without getting too much volume averaging over that detector. So leakage, you can think of it in two different ways. There's the transmission through the leaves and then there's also the interleaf leakage where you have some areas between leaves where you'll have more leakage and then in the middle of the leaf where you'll have less. So often the treatment planning system will use just the average leakage. And in this case, the measurement for the leakage should be one that is with actually a larger detector as opposed to a smaller one so that you can kind of get an average number for that. So for the MLC penumbra, the leaf position may be calibrated at the actual position it may be calibrated at the 50% dose profile or it could be calibrated at the position that gives the most uniform profile when it's closed. And so here's an example from, I think from the Estro guidebook where you have different profiles. These are different profiles that you get from summing the dose from one leaf from the abutting leaves when those are at different positions. And so as you can imagine where you define your leaf positions will determine what the dose looks like at those adjoining leaves. So the most important thing here is to make sure that how the linear accelerator defines this and how the treatment planning system define this are the same. So they're talking the same language as far as your leaf edges go. The dosimetric leaf gap or dosimetric leaf separation is, this is something that is introduced into some of the treatment planning systems to match the linear accelerator. And what this is is it's an offset between the, let me see if I have a, it's an offset between the actual and the modeled leaf gap that you use to match the dose between the two. So here's an example. So this is how we measure this where you have some gap between your leaves and you have a motion where this starts over and it sweeps across the field. So you have this leaf gap and you sweep it across. And then you measure somewhere in the central, in the central part of this field, you measure the output. And then you vary the gap size. So you'll get a measurement, an output measurement for this sweeping gap as you go across. And then you vary that gap size so you have different amounts of gaps. So as you can imagine you have this, you have some effective basically field that is delivered, but it's delivered instead of a certain number of model units with an open field, you're sweeping this gap across. And then once you do that, you get this plot. So here you have a gap of 10 centimeters. Here you have a gap of two centimeters. Here you have a gap of five centimeters. And this is the output that you measure. This is the measured dose minus the leakage because you're gonna have a lot of low dose in that measurement. And so you subtract out the leakage from that. And this is with an output with a ion chamber. And so here at the end, you're gonna have some sort of an intercept. This isn't gonna be at zero. And so what that means is that we're not having, we don't get zero output at zero gap. There's gonna be some sort of a gap there. So we're basically measuring this gap. And so this intercept of this line here if we do a linear fit, that is that leaf gap, that dosimetric leaf gap. So there's a few tests that were developed for dynamic or this dynamic IMRT where you have a sweeping across the field. And these include tests for leaf speed because now as opposed to step and shoot, we have some motion across as we are delivering these fields. So we care that we have an accurate leaf speed and that when we care that the position is correct as a function of monitoring units as that field is delivered. So this test here that is suggested, basically you have one centimeter gap and it slides across the field and you deliver that with different number of monitoring units so that the leaf speed changes. So if you deliver a few monitoring units you're gonna have a very quick speed across. If you have a lot of monitoring units it's gonna go very slowly across. So when you do that, you should have, and if you put a chamber at the center of the field and you measure the output, you should get the same number, well you should get a number that's directly proportional to how many monitoring units you deliver. So that's a suggested test for leaf speed. So another thing to think about for IMRT commissioning in the case of physical compensators basically there's attenuators if you're using brass or some type of compensator the treatment planning system needs to account for, so this is not MLC based, for the beam hardening because you're going to have a different distribution of your different energy spectrum basically as that compensator gets thicker and then also scatter from the attenuator and how does the treatment planning system account for that? And then that's on the treatment planning system side. For the delivery system, it's important to think about the, what material is gonna be used for those compensators? How are they, is this a standardized process? How is it gonna be, how's the record and verify gonna work so that you don't mix those for different beams and how do you make sure that the field one, compensator is used for field one and not for field three, so on and so forth. And then also the machining accuracy and the placement accuracy, how accurately can these be built? And when you put them in the head, does it always go to the same position and the correct position? All right, so this is a figure just from a task group the recent task group just on quality assurance for linear accelerators and you can see here, you have, they have broken this into a non-IMRT machine and IMRT machine and SRS SBRT machine. So the basic takeaway here is that in many cases, IMRT requires stricter tolerances for the machine, for just your normal machine quality assurance that happens than a 3D case or a 2D, a machine used for 3D or 2D would need. And so that's important to be aware of. The reason for that is because we're shaping that dose distribution very carefully and very conformally and so we can't allow as much play in some of these variables as we could with a 3D case where we might have more room to work with for the dose as far as shaping around the target. All right, so for the treatment planning system, it's important to separate out the planning system and the delivery system and the commissioning of those. If you're very confident about the delivery system and that the output is correct and so on and so forth, the flatness symmetry and then if you see any differences between the planning system and your measurements, that helps to be able to separate where those errors are coming from. So IMRT is an extension of 3D treatment planning. So because of that, it requires the same commissioning requirements as 3D planning plus some IMRT specific tasks. So some of those IMRT specific tasks include, now you have an inverse optimization that's included in the planning system. And so because we're using an inverse optimization that is based on these contours and it's based on the contours that are made by the physician and by for the OARs and it's all in the DVH space, that requires an accurate calculation of your DVH and that those contours are defined correctly. So some of these are not things that are typically verified by a single institution but more of a user's group and it's kind of an interaction between the vendor and the physicists and of all the different institutions using their software, just making sure that these are done correctly. And there's a lot of guidelines as to doing this but it's not anything that one institution typically does. Besides maybe a quick verification that it's calculating something correctly. More importantly is the leaf sequencer. So a leaf sequencer, this is what's gonna take the fluence and turn it into an MLC shape. Now this is usually commissioned together with the planning process. So you treat this as part of the planning process as opposed to commissioning it separately. However if you get a new leaf sequencer, like a new algorithm that the vendor sends that may require repeating some verifications that were done during the treatment planning system commissioning because this is really part of that, that whole process. And then finally there's the dose calculation which is important both for 3D and IMRT. So for the dose calculation, there's a few things to consider. One of those is the leaf positions in the treatment planning system as we talked about before. Also beam profiles for small segments in a budding fields. And then profiles for small fields for sliding window and also the tongue and groove effect and leaf transmission. And how is it a count for these and putting those numbers in so on and so forth. And then finally small field output factors and the depth dose curves for those. Notice how is that inputted into the planning system and so on and so forth. So these ones down here, it's those distributions for typical site specific fields. This is a good thing to verify that we'll talk about in a minute as well as representative test patients. So this is some of the estro guidebook recommendations for verifying that treatment planning system. So they suggest starting, and this is a good suggestion, starting simple, so you start with something simple. Like a single beam on a flat phantom, well first start with 3D cases. And once you've done that, start with a single beam with a flat phantom with some controlled intensity pattern. And then you can make that more complicated and you verify multiple beams on a flat phantom with different intensity patterns. And then treating some sort of a hypothetical target. So now you've not, in these first two, you're basically telling it what fluency you want. And here's some examples they give of different intensity patterns that you could tell the leaf sequencer to create a sequence and deliver and then you just verify that. So you would say, okay, I put this in for one field and now I put some film down there and I measure it and you know, you're verifying that you're, when you put this in the planning system that you can deliver that. Either a point dose measurement or 2D or combined so on and so forth. And then moving on to multiple and getting this more and more complicated to you get to kind of treatment plans that are in some sort of a complicated phantom or anthropomorphic phantom and verifying that. So basically those are increasing complexity and starting with the first ones that are basic and then going and then getting more complicated. So the goal of this is really to verify the accuracy of the beam parameters in simple, easily analyzed situations. Something where if you see an error or you see a difference between the two that you can easily tell where did that come from. If you have, if you start with something very complicated and you see a difference, it's gonna be very difficult to say, oh, this came from, you know, my, my MLC positions or, you know, my leaf gap was, I need to adjust or so on and so forth. And then this also helps to determine the level of accuracy that can be expected in clinical situations, as far as in the later stages when you get to the more complicated ones. So here's an example that they give of a leaf sequence and with this intensity pattern delivered and then measured and you can see here, they have some slight differences there, but you know, this is the sort of thing that can be done where you have an intensity pattern, you deliver it, you have a calculated, you have a delivered and you can compare. All right, so the other thing I'd like to talk about a little bit is this test suite, this, from this task group report 119. So this is a very useful set of tests that are available for IMRT commissioning. And what this is, is this task group report had a bunch of different institutions and they all did film verification for different types of IMRT cases that were meant to simulate clinical situations but in a phantom. And so they have, and they provide this test suite so you can actually go download this and get the geometries and get the plans. And they also give optimization constraints and the structures there in some square kind of solid water phantom. So this is something that's very useful. And then in addition, they give the agreement rates that all of these different institutions got. So then you can kind of compare to that as a kind of a baseline. And as well as planar dose measurements in film and point dose measurements with ion chamber. So here's some of the examples the test suite includes the basic field like an APPA. So just two simple fields, bands, which is this one here where you can see it has intensities for different intensity levels going through the phantom in just two dimensions. So basically in this dimension here. And then they have multi-target plan, a prostate plan or I should say simulated prostate plan, a simulated head and neck plan and then this C shape. And there's an easy and a hard version. The only difference there, they're the same shape of the structures, but they have different optimization criteria. So one of them you're trying to get, you have an organic risk that's close to the target and you're trying to, one of them is very easy to get. And then the other one is much more difficult. So you have a much more complicated fluence pattern trying to lower the dose to that organic risk. And here is the example of the multi-target. So you've got one, two, three here. Targets all lined up in this square phantom. Here's the C shape. So you have this target here and you have an organic risk here that's basically wrapped around by the target. And then you just, you have an easy and a hard version where the hard version, you're limiting the dose to that organic risk much more than with the easy one. And then here's the mock prostate case. So you have a, the colors aren't very good here, but you have a bladder and a prostate and a rectum. So basically three structures there. And then the head and neck where you have some other ones simulating parotids and cord and then just some volume there. So these are all geometries that you can download. They already have the contours. And then you would just do the planning portion and then the delivery and then verify your planning system calculation versus what you measure with film. And here's the, so this is all the multiple institutions that did this. And there's a lot of different technologies being used here and delivery techniques and planning systems. So it's kind of tested over a lot of different possibilities there. So here's some of their results. I'm not gonna go too much into detail here, except to say that, you know, they were able to get their point dose measurements within two to three and a half percent. And if you notice the one that was three and a half percent off, that's the, that's this harder C shape. That's the most complicated plan. So basically the easy, the easy plans should be, you should expect more agreement than the more complicated plans. That's where there's the largest uncertainty in that measurement there. And for the most part within two percent, so that here's the organs at risk. They have some measurements in the organs at risk and they're within two percent of the prescription dose. The, the uncertainty is about two percent of the prescription dose. And here's their results for, for film. So they're basically giving a gamma criteria for film. So these are just some baselines that can be used to compare. And this is all in that report that you can, you can go down though. All right, so, dosimetric verification for per plan or per site. So what to do when we have a new IRT technique that's introduced. So let's say you've been treating, maybe you already are doing IRT, but you're going to do a new, new type of IRT, a certain type of case that maybe you haven't been doing head and neck, but now you're going to or something like that. So what we'd want to do in that situation is prepare a sample of representative treatment plans. And then that helps to solidify some of the details that'll go into the treatment planning, the delivery and the QA processes. And then make a thorough set of verification measurements for those sample plans. And the goal is to be confident about the robustness and the dosimetric accuracy for this new technique. So once again, here's this kind of pyramid. In this case, with this new technique, we can start with something that's maybe a more comprehensive measurement. And if it looks great, then maybe we're okay. If we see some discrepancy, we can work down to more fundamental measurements. So another thing that I just like to mention briefly, there are some credentialing that happens for being involved with certain clinical trials and so on and so forth. And these can be useful independent checks of how accurate they are. The most basic one is an absolute dose check that's offered by RPC in the U.S. I don't know if there's other equivalents, but I've heard of also, for example, some CyberKnife centers that do kind of local independent checks. So this is always a good idea where two different centers maybe can compare or can go over and measure the dose independently for and verify the accuracy so that you're not just working in a vacuum, but you're using another center to get their expertise and verify across each other. So this is some sort of independent check can be very useful to verify that you're not way different than all of your neighbors. So finally, pretreatment verification. So the idea with pretreatment verification is determining is basically we verify the dose and the MLC positions in some way with some sort of a measurement ahead of time for these IMRT cases. For the commissioning, we need to determine a pretreatment procedure. So what procedure is gonna be done for each case that comes up? And that should be determined in the IMRT commissioning. And then as well, what sort of action criteria? What's an acceptable level of agreement to be expected for that? So there's a lot of different questions that need to be answered in that commissioning. What detector is gonna be used and in what geometry? Is it gonna be in a phantom, in air? And is the measurement noise at an acceptably low level? Can you get a good agreement? And is the detector and geometry adequately sensitive to dose discrepancies? And then what analysis is gonna be done? Are you gonna be a dose difference or distance to agreement, gamma analysis, so on and so forth? There's a lot of different questions there that should be answered and there's a lot of literature as well that you can look at to say what's being done or what acceptance criteria is acceptable or expected and so on and so forth. So all this needs to be determined as part of the commissioning process so that when a new IMRT case comes up, there's already a procedure in place that you can go through and it's ready to go. So there's different types of verification that can happen and this can be typically a phantom-based verification. So basically what you have is an IMRT plan on a patient, now you're gonna take that same IMRT plan and calculate the dose in a phantom geometry, something that's easy to reproduce and then deliver it on that phantom geometry and then compare the plan and delivered. Other possibilities are something that's like maybe just a beam-side view where you're just verifying either the fluence or usually the fluence in two dimensions at each gantry angle or you just set the gantry to zero and just verify fluence. And then types of measurements, there's one dimensional, two dimensional, like one dimensional, like a ion chamber measurement, two dimensional film, some other types as well and then there's some 2D plus as I put them which are, there's some detectors out there that are able to measure in multiple planes. These are typically used for VMAT type cases where you have the gantry rotating the whole time. And then there's kind of one academic side, there's some 3D dosimetry techniques that I may mention here briefly. So for ion chamber basically, for an ion chamber verification, this is the simplest, it's also very useful. Basically you're measuring the charge, you first measure the charge in some known conditions. So you have, you put your ion chamber in and you measure for maybe a 10 by 10 field, you know what the dose should be there and you get a charge. And then you measure the charge at a point in the IMRT plan with that same chamber and the dose to the IMRT plan, you basically cross calibrated to your charge using your charge in the known geometry. And then you can compare the dose to that IMRT plan to the dose that's expected from the treatment planning system. This is a figure from the Estro document, just showing here the agreements that they have for a bunch of different measurements for ion chambers, 1D measurements in IMRT. And the one thing that they note here is there's less correlation for the farmer chamber as opposed to other smaller detectors. And this is due to the lack, probably due to lack of scatter equilibrium. So a smaller chamber is probably more useful because you're measuring over a smaller volume, there's less averaging going on in that volume, especially for cases with IMRT where you've got maybe this strange dose distribution, lots of gradients, so on and so forth. And you can see here the accuracy that's expected here or that they're getting is more or less within 2%, 3% that we should be able to measure with an ion chamber between the agreement between the planning system and a measurement in phantom. So some of the uncertainties in this ion chamber measurement, there's some differences in stopping power ratios that those can be assumed to be negligible. In the Pernumber region, if you have a large chamber and you're in the Pernumber region, you can expect large differences. So we try to use small chambers in the high dose area. We may be in the Pernumber for one field, but if it's 9% but we have multiple fields, that's probably going to average out. And if the composite dose were in the high dose area, we can expect to have much less error. So some of the ways to minimize those errors is using a small volume chamber, calculating dose to a volume rather than the point in the treatment planning system and then avoid measurement in areas with large dose gradient. And so they suggest here that the small volume chamber, standard uncertainty should be one to one and a half percent. So just a few notes here. Basically, ion chambers are a great way to verify this. So 2D measurements, there's a couple of different ones. I'm gonna talk quickly here about film, radiographic film, radiocomic film, CR. There's some papers looking at showing that you can use CR for this with some uncertainty. And then there's some 2D arrays that exist that these are diode or ion chamber arrays or your portal imager that can all be used to verify IMRT. So film, here's an example of radiographic film. It comes in this pack and then you have a developer that it gets developed. It has some advantages, it has high spatial resolution. And there's some uncertainties due to lack of water equivalence and energy dependent depth. But this can be minimized by measuring perpendicular to the beam at a set depth. But if you're doing an IMRT plan with multiple fields and you're trying to do a composite, that's something to keep in mind. And it requires basically, you have to have some curve, you measure the curve where you have different dose levels and you equate that with optical density and so you get a calibration curve to convert this optical density to dose. So radiocromic film, this is, has the advantage of, you don't need a developer for this and it's nearly tissue equivalent. So it has some advantages there and it can be scanned out with a flatbed scanner. And so this is also a very useful thing that can be used for verifying dose in multiple dimensions. And this is for, one thing to note is for commissioning, when you're doing the commissioning for IMRT, you're gonna want to be more comprehensive than probably for your per patient. So when you start out, you're gonna want to verify everything very carefully that you get good accuracy. Once that's verified, you don't have to be as comprehensive in your measurements for a per patient basis because you've already done a lot of work up front. And so here's just a few, basically the protocol that's used for this and this is all in the guidebook that you can download and look at. Here's an example just showing a, not cylindrical, but kind of a patient-shaped phantom with a film in there and the measurement. So you can see here the dose measured and calculated and you can get a dose difference. Very useful things here for verifying dose distributions for IMRT. So just a few notes about CR. A lot of hospitals may or may not have CR for diagnostic purposes. In theory, this can be, go ahead. Oh, okay, three minutes. I'm almost done here. So CR, you can use that if you want. 2D arrays, you can use those as well. They are, these are great tools usually used for planar measurements where you have the gantry just at zero and you set it on the table at a certain distance and so you're just basically verifying the fluence for each field and there's lots of different versions of this that are available. Portal imagers, so basically that's this portion here. You have your Linux head and then your portal imager. These are typically amorphous silicon flat panels. These are very useful. They have fast response, high spatial resolution. A lot of vendors have their version of portal imaging and verification for IMRT. So this can be a very useful way of verifying per beam fluence for IMRT. Here's an example of variant software. Basically, you have a measured fluence from the flat panel. You have a calculated fluence and then it has all these fancy tools for comparing those and then you can get kind of a, an agreement, different ways of analyzing and getting an agreement. And so it's all built in and very useful. Here's some examples of these, what I call 2D plus arrays where you have, this one has this kind of circular bit of arrays and this one has two arrays in kind of shaped as an X. So these are all other tools that are out there that can be used. 3D dosimetry, new 3D dosimeters have overcome a lot of the challenges of prior 3D dosimetries such as these are rigid now and high resolution. There's no dispersion of the signal. There used to be a problem with gel dosimeters. There's no oxygen independence. These are, you know, and then there's also new ways, they have these new telecentric lens optical CT. They can read these out very quickly, but these are very kind of academic. These may be useful at the most, I would say, in the IMRT commissioning stage where you've never done something before, but even then I would say they're rarely used. It's more kind of academic. And here's an example of their reconstruction software. So they have some, basically this is optical CT. They reconstruct a 3D dose distribution from these 3D dosimeters. All right, I'm done.