Can you introduce yourself?
My name is Justin Macal, and I’m a certified medical dosimetrist with CAMP. I’ve been a dosimetrist now for a little over a year and a half.
How did I become a Dosimetrist?
I started out as an x-ray technologist, went to x-ray school, did my rotations through all of the modalities within x-ray, so CT, MRI, cardiovascular, therapy, and dosimetry. One thing that stuck out to me was the therapy side. So from X-ray tech, I became a therapist and did that for several years. And once I got into the therapy world, really mastered that workflow and duties of radiation therapist, I just felt like there was a little bit more.
I never actually thought I’d be a dosimetrist. Actually, my first rotation in dosimetry as a therapy student, I didn’t like it. But, and this is my opinion, it was Pinnacle. So it wasn’t very fancy and it reminded me of the 8-bit Atari video games.
It is a very great planning system, but it just didn’t appeal to me at the time. I didn’t want to sit at a computer and contour and make plans. But at the end of the day, what I didn’t realize is that dosimetry is like a problem-solving game every single day.
That to me is very appealing. As a therapist, I really excelled in CT Sim. I really liked those hard sims where you had to think of a creative way to set up the patient to ensure their comfort and allow the dosimetrist to create a good plan.
So that problem-solving really appealed to me. And dosimetry really is the next level for problem-solving. You’re kind of an artist in that sense, creating a plan, painting dose, making things informal, and treating the tumor.
So from there, got my bachelor’s in radiation sciences through the University of Iowa, practiced as a therapist for quite a while, and then got into dosimetry, got my master’s in medical dosimetry through John Patrick University.
Now I work in the clinic as a certified medical dosimetrist, and I’m also an adjunct instructor for VMAT, IMRT, SRS, and SBRT at JPU to help future dosimetry students prepare for the clinic and develop strong planning skills from the start.
What is Medical Dosimetry?
It’s a very broad question, but the center of dosimetry really is high-quality treatment plans and getting all the information together to create that high-quality treatment plan.
We need a lot of information. We need all the outside imaging that you might need to do image fusions for the doctor so they can properly delineate the tumor. And that also ranges from prior radiation dose.
So finding where that radiation was done, getting that dose, getting those DICOM files so you can know where to avoid if that potentially overlaps your new tumor volume area. We’re gathering all the information, setting the doctor up for success to delineate an accurate tumor volume, and then using our skills and techniques that we’ve learned to create a very effective and efficient plan for the patient that’s safe for the patient and deliverable.
You can create a beautiful plan with 20 beams, but that’s not realistic. We have to make sure we create an effective plan for the patient that they can tolerate for 10 to 15 minutes, so they’re not moving because patient movement is probably one of the biggest random errors that we need to account for. So if we can create a high-quality plan that’s also efficient and effective for the patient, that’s the bread and butter of dosimetry.
How does medical dosimetry fit into the larger medical physics ecosystem?
So dosimetry and physics work hand in hand. We’re really a team. We’re not really separated aside from QA. I’m not doing QA on the machine, but physics knows dosimetry, and dosimetry should know some physics.
We need to know radiation physics, and physics is the master of that. So we need to work together to know the right beam energies, the correct beam geometry, what’s actually deliverable, and the right machine limitations.
We need to take all of this into account, working with the physics team, in order to generate those amazing plans and safe plans for the patient. So the ecosystem between dosimetry and medical physics is very intertwined.
We should really be working as one, and we do work as one because we need to check and balance each other and make sure that we’re putting forth the best possible radiation plan for that patient.
What is the typical workflow for a Dosimetrist?
So the typical workflow for a Dosimetrist starts in CT Sim.
I’m a hybrid dosi, so I do two days remote, three days on-site. Those on-site days are very good, very critical. We, as dosimetrists, can be in there at CTSIM to ensure that therapists are great.
They’re going to do the job that they need to do. But what we need to also realize and understand is maybe the best, the most practical setup for this patient isn’t something that we can actually treat and deliver.
So as a dosimetrist looking at CT Sim, we need to make sure that we’re getting all the information that we can. What I mean by that is not clipping certain tissues in the body that would prevent us from putting a beam on.
Because we need to make sure that we have all of that tissue so we know the depth of where that beam is going to enter the patient. So if anything’s cut off, we can’t use that area as a potential beam point of entry.
So we need to make sure we have all the information possible. Also, we need to take into account that if we clip some tissue and the technique jives with what we had to do for Sim, then it is what it is.
At the end of the day, we are making sure that the quality that we receive is good so we can put out great quality plans. Garbage in versus garbage out, we’ve heard that term many times.
We need to make sure that we’re getting high quality information in, so we can put quality information and quality plans out.
The next step in that workflow from CT-SIM would be image fusion.
Typically, for a palliative case, you might not have many images diffused. We know where the patient had pain, say it’s a spine area, we can just deliver a said dose to the spine. No imaging is really needed there, even though it could help.
But the more complex cases, the more standard cases that you’d see come in, right, like prostate, head and neck, brain, you’re probably going to have some sort of MRI or PET scan. So those are very common imaging modalities that will fuse with those scans.
What I mean by fuse is if the patient came in we’re going to take that fusion and we’re going to overlay it and match it up perfectly to the area of interest where we want to treat. The doctor can accurately delineate tumor volume for us, and also those images allow the physician to see the subclinical disease. CT is very fine, we can see really good soft tissue resolution. But MRI is even better, right?
So let’s get that MR in there. If they have it, let’s get it and set the doctor up for a better chance to see that subclinical disease so they can give us accurate tumor volumes.
PET demonstrates the metabolic qualities of a disease. We can see the activity, what’s going on, things light up in the PET. So that’s another great modality that we can use to also overlay on the CT to more accurately generate tumor volumes.
Another thing that you may encounter would be prior radiation dose. You’re going to get those prior RAD records, hopefully in a DICOM format. So you can bring that DICOM in, do another fusion, and then overlay that dose on the new CT. It even helps the physician if it’s adjacent to where they’re drawing a tumor.
The physician is going to know up front where that dose was. Then in a planning aspect, they’re going to know that you’re not going to enter through that dose so if you get a scenario where you have to avoid certain sectors of that prior RAD dose, the physicians are already aware of it.
So it makes the dosimetrists’ job a little bit easier, knowing the expectations coming through. So once we get all that imaging in, we get the targets drawn by the doctor which gets sent back to us and then we’re going to make that treatment plan.
The type of treatment plan that we decide sometimes is dictated based on the region that you’re in or the type of patients that you have, whether they have the Medicare, Medicaid, or commercial insurance. That may dictate what type of radiation technique you can use. Those techniques are 3D, 3D conformal, 2D, IMRT, VMAT, SRS, and SBRT. So typically, we have pretty free rein of what style we can use. But there are times when you want to use that highly conformal technique of IMRT, VMAT, or SRS, SBRT, and insurance won’t pay for it, they won’t approve it. We can still create conformable plans with 3D, but it’s a little less efficient for the patient on the table and could take longer to deliver. We can still create a beautiful 3D plan, but it’s going to be a lot of beams. What a lot of beams means is it’s going to be a longer time on the table. And we all know that the longer the patient sits on the table, the more errors of motion and more chance for the patient to move.
So if we can create a quick, conformal plan for the patient, reduce that time on the table, at the end of the day, it’s going to be more effective for the patient, safer for the patient, and give us more peace of mind, right? Because we know that we created an effective conformal plan and didn’t give the patient a lot of time to move on the table. Eliminate that factor. So the dosi generates that plan based on what technique they choose.
And then that will go on to some sort of review. At least in my scenario, we have a physics review. So here comes that dosi-physics relationship. We’re going to do a very fine, detailed plan review. We’ll make sure that our nomenclature is correct, that our beams are oriented and labeled correctly and that we have the correct dose. Obviously, evaluate our DVH to make sure that we’re adequately dosing the tumor and greatly sparing the OARs.
OAR is very important there. Then we’re going to look at overall plan quality. We’re going to make sure that our low-dose isodose lines are tight and that the our prescription dose to the target is conformal.
We don’t want that bleeding out anywhere into adjacent OARs and potentially overdosing it in that area. So we’re going to make sure things are tight. Once that’s done and the plan looks great, typically this is where the dosimetrist isn’t really involved, but in terms of what’s happening with the plan, it may go through some sort of QA quality assurance testing.
For VMAT IMRT, it’s required in the United States to do some sort of patient specific QA on the machine. So whether you use portal imaging or an ArcCheck or whatever QA device your physics team uses to verify that dose, that’s what’s happening there.
For 3D plans, it isn’t needed, but for IMRT, VMAT, SRS, SBRT, we’re doing some sort of quality assurance check to make sure that what we planned is actually what’s being delivered. And then from there, it’s to the treatment, to the therapist side.
And with that our jobs are done. We’ve made sure that we’ve created the best, most effective, and efficient plan for the patient, dosing that tumor and sparing all organs at risk. That would be a typical workflow.
Why is medical dosimetry important for patient care?
Dosimetry takes more of a back seat but it’s critical. As a therapist, you are the front line. You are kind of the face of the clinic in a sense. You are dealing with that patient anywhere from one, five, 10, 15, 30 fractions a day, so you develop a very one-on-one relationship with that patient. That’s very important for that patient in terms of real-world impact.
But for the dosimetrist, we kind of take a step back outside of that direct patient care. Our job is to make sure that we create the most effective and quality plan for the patient. So that’s the real world impact.
Quality. So that’s our goal. That is our motto, our mantra. That’s what we need to live by, right? We need to really treat every patient like a family member and give them the best possible quality plan, and have that cross-checked by the entire team to make sure it’s effective and deliverable.
If you put through a great quality plan, in theory, those patients are going to have great results.
What are the realistic expectations of a new grad dosimetrist coming into your group or really coming into the field?
So that’s a great question. I think as a new grad coming into the field, you also have to have your own set of expectations. Not every new grad is going to know it all, and that’s okay.
What every new grad should be comfortable with is their knowledge of dosimetry and have a good foundation. All of the programs out there teach the information; it’s up to the student to take in that information and be able to replicate that in the treatment plan.
At the end of the day, as a new grad student, have the confidence of what you were taught and what you learned. Then just put that forth in the treatment plan. Let’s go over the scenario where maybe you are a new grad and they’re hiring you in as a solo dosi. One question that I would ask the hiring clinic is, where’s my support group? What kind of support will I have? Because I wouldn’t expect a new grad to know how to plan everything A through Z. I would expect there to be a little bit of a learning curve but the foundation should be there. Let’s say that you have a great support group. Like in my scenario, I’m a solo dosimetrist at a clinic and we do have other dosimetrists helping fill in if the workload gets a little higher. However at the end of the day, I have access to multiple dosimetrists and multiple physicists across a lot of clinics. So in my scenario it works really well since I was a new grad, supporting a clinic on my own and I was set up for success. I was able to learn things very quickly, which I think is great but at the end of the day I had a very strong core knowledge set. I knew what was expected. I knew the radiation physics behind the plans. I knew what was possible. So as far as approaching something I didn’t know how to do, whether it was a treatment site that I haven’t worked with yet, down to its core, it comes down to the radiation physics that you learned in school. So apply that across all of the techniques across all of the body sites and you’re not going to have a problem and when it comes to optimizing. The optimizer will do what it’s told and it will put dose where you tell it to put it. As long as you have those planning techniques and the correct foundation to control that dose, apply that across every body site.
So have that confidence that you know what you’re doing, and make sure you have that support system if you do need to reach out. And if you don’t, you have me, you have your classmates, you have every instructor that you’ve been in contact with. It doesn’t need to be the clinic that you’re at. There is a dosimetry community out there that will help anyone in need.
What are the true benefits of using five arcs on areas like head and neck?
Whole brain hippocampal sparing, yes, I would advocate for that. Sometimes pelvis cases. Are there any statistical benefits worth the extra treatment time for the patient? This is a two-part question here. To just talk about the arc situation, let’s focus on head and neck. If it’s unilateral, one side, two arcs all day long – two partial arcs.
So something from maybe just past zero degrees, whether it’s 30 or 345, 330, and then arcing down 179, 181, right, whichever side it’s on. So two partial arcs and a unilateral head and neck case I think is reasonable, depending on if it’s single-dose level, two-dose level, three-dose level SIB case.
You could argue that size is definitely a factor in arc selection. For example, in head and neck cases, you’re never going to have a field that extends beyond 40 cm. So, I don’t really see the need to use more than two arcs for a unilateral case.
Now, let’s say head and neck bilateral; it’s the worst possible scenario. It’s a large head and neck case, bilateral, three dose levels, SIV. In those cases, I’m probably going to do three arcs, probably three full arcs, centered in the center of that ISO and center of that PTV. I’m going to do some sort of flip-flop technique where it’s 15, 345, and a 90. That 90 focused on the high dose portion or your tumor volume for that low dose volume near the trachea is going to be a U shape. Physicians like to see that low dose carved out near the trachea, that 90 degree focused on the bottom half. If you can include the high dose area in it and maintain your 15 cm jaw max, if you’re using a Varian, 120 MLC, then you should be fine. When it comes to arc selection and how many, it’s going to come down to your machine limitations, size of PTV, and what you’re given. I don’t think I would ever need to use five arcs on that sort of case. Probably three arcs max, four arcs.
If we were asking something really crazy, like sparing both submandibulars that were partially covered by the PTV, let’s say, right, we might need to do something a little more fancy there. So maybe that additional ARC on the three ARC plan, making it a four ARC case could be argued. However there’s no real answer on this. If your clinic’s used to doing five ARCs, that’s what they’re used to. I’m not telling you to go change your workflow and change what people are used to, but I will tell you what’s efficient and effective, and that’s my opinion.
For statistical benefits, it comes down to MU, modulation. One thing we need to think about when you go from three arcs to, let’s say, five arcs, six arcs is the machine can only rotate around the patient so quickly. The MLCs can only move so fast. So in a case where you’re delivering, let’s say 200 cGy per day, that 200 cGy has to be split up between three arcs, four arcs, five arcs, six arcs. So in order for that machine to deliver that dose and split it up between, for example, five arcs, there are three things that we need to remember. First thing is we are limited by how fast the machine can rotate around, how quickly the MLCs can move and the dose rate.
So one of those three are going to change in order to deliver that dose. So if you have five arcs, you could be in the scenario where it’s under-modulating, which means the machine’s just trying to deliver that dose split up between five really quickly. Then you could lose effective modulation because the machine is just trying to spin so fast. Now, if there’s a lot of modulation that’s required, then the machine may slow down and deliver that plan. But is it really effective? Is it really doing its best job that it could with three or four?
That’s hard to pinpoint exactly, however the facts are you’re limited by those three factors and the more beams you add the more the machine’s going to have to figure out does it need to just slow down its dose rate, speed up its gantry and is it limited by how fast those MLCs can travel.
If you have an SRS case, 1000 cGy or 2000 cGy in an SRS, typically, those usually don’t require a lot of modulation, though if it’s right on the brainstem it does. In those cases, you may be able to get away with more beams because there’s more dose to spread between those arcs, there’s more real estate to use between those beams per se so you wont run into those issues. You’ll notice it in modulation and probably hotspot when you’re doing, for example, the 180 centigrade a day with 5 arc plans.
What are your thoughts on gEUDs? For example, using an upper gEUD with an alpha value of 1 to control mean OAR constraints or an alpha value of 40 to control max OAR constraints or even using target GUDs on PTVs.
To knock out that last one, I don’t use target GUDs on PTVs. I’ve experimented with them and there’s a lot more target GUDs you need to put on the target in order to make it reflect what could be done with a DVO or dose volume objective. I’m not going to get into using target GUDs because there’s a lot of unknown there. However, there are some benefits, but not in terms of getting a minimum dose to the target and a maximum dose. You’re better off just using DVOs in that scenario.
There are a few tricks to control 105. There’s a GED value for a target GED value you can use to control that works really well. Again, this is just my opinion, and I don’t use it often so I’m going to stick with what I know. I can control all of that with several different DVOs on the target, which you could also argue is exactly what a GED does, right? For example, alpha value 1 is exactly like a mean constraint DVO, so you’re not doing anything different there. Those are the exact same – they perform the same, they behave the same. However the upper value 40 to control max OER constraint is the DVH line going down.
Let’s say I’m trying to control a 50 gray max on this on this line on the DVH so I may in the optimizer, I may put a DVO of 49, 50, something a little under or 50 gray let’s say that’s just going to be one point on that tail at 50 gray so that’s just going to work on one singular point. If you set that priority and watch your cost function, you can achieve the goal. What a GEUD with an alpha value of 40 does is add control points to the tail of the DVH curve. The lower the alpha value, the more points it applies along that tail. At 40, it places several points on the end of the curve for maximum dose control. At 39, it moves further up the tail. At 38, even more.
On an OAR, I’ll stick with 40 or 39 because I don’t want to start creeping into either the shoulder or curve of that DVH. I want to focus on just that tail coming down. And the GUD really, is better sparing on that because it’s going to be working on more dose levels. It’s more powerful. It’s going to penalize your overall cost function more. So your plan is going to be working, and the optimizer is going to be working harder. If you’re already asking a lot from the plan and you have a lot of GUDs, then you might be overcomplicating it.
So then in that sense you may just want to stick with one singular DVO and escalate the priority to get what you want. I use DVOs in all my plans. I was exclusively on both plan challenges in 2024 and 2025 and achieved top Eclipse plans both times. It’s really just what you prefer and what you want to use. I’m not going to say I couldn’t have done it with GUDs. I think I could have, it’s just not my style.
How did you get into radiation oncology and medical dosimetry? What’s your favorite body site to plan and why?
So it’s funny, people that may come across this video and hear, “what’s your favorite body site to plan?” will think it’s a weird question, which I get, but I think every dosimetrist does have their favorite body site to treat, which is kind of a morbid question. But, you know, we do! So I would say my favorite body site, not necessarily body sites, but treatment technique, would be SRS, SBRT. I really like escalating high dose into the hypoxic center of a GTV, really taking advantage of that therapeutic ratio inside the cell where it needs that high dose. So that to me is appealing, right? We’re taking radiobiology and mixing it with our treatment techniques. And I think that’s really fun. So I really enjoy SBRT lung cases, bone cases, brain cases, and driving that high dose into the GTV because I like taking advantage of that therapeutic ratio into the hypoxic center of the GTV. So that’s why I like that site or that technique.
How I got into dosimetry I have touched on a bit earlier, but in summary I did rotation therapy, which I didn’t like. Then I got into the planning system, sat in a dark room and contoured for two hours, didn’t really plan a whole lot and I didn’t think I could really get into this. But as it turns out, dosimetry gives me a new problem to solve every single day, whether it’s finding the records, fusing an image, doing a great treatment plan, or even helping other people create great plans. So it’s all problem-solving, finding the best solutions. So that’s what kind of got me into the field. And that’s what made me really love the field is the problem-solving aspect. I realized that there were more problems for me to solve, because I really enjoyed CT sim, like those tough cases where you have to think of creative ways to construct a back lock, and aquaplast masks, and tongue depressors, custom mouthpieces, things like that. You have to make things right and solve a problem. So translate that into dosimetry. That’s what we do every day. So that’s how I got into it. And, you know, that’s why I love it.
What would I consider the most difficult cases to plan?
There isn’t any site that I think is difficult because every site that we have, that we’re given, the basics are all the same. The physics is the same. The CT dataset is the same ones and zeros. I’m using the knowledge that I have in dosimetry and applying it across all the sites. So there isn’t specifically a case that’s the most difficult, but I would say the hardest things to plan are any site with prior dose. Because anytime you get something with prior dose, you already have one hand tied to your back if it’s adjacent to the tumor. So either you can’t enter it or you can’t exit through it. So anytime that the dosimetrist is limited by their degrees of freedom and where they can put a beam, it makes the case 10 times harder. So to answer that question, the prior RAD would probably be the hardest cases to plan because we have to account for what happened previously. and it’s not something that I can control up front.
Have you planned lattice treatment before? Any tips? Yes, I’ve treated lattice. We’ve done it a handful of times at our clinic. It’s a great technique to use on bulky tumors that are relatively radio-resistant. The whole lattice theory is we’re taking advantage of that bystander effect and not only using that high dose to create DNA, Single strand, double strand breaks, but we’re also utilizing that low dose. So you’re getting, in a sense, two types of radiation killing and this is all done in one plan or one shot, usually like 20 gray or so. So I think that’s a great technique.
The hardest thing for these cases is just knowing what to do, right? It’s not new. We’ve been doing this for a while, but not a lot of clinics are using it, mostly because we don’t know what the standard is. I recently attended 2025 AAMD and we had a talk on grid therapy, SFRT. The presenter actually developed the dot decimal brass block that they used for one of the first grid treatments. The brass block that you attach on the machine has a lot of little holes cut into it. You can deliver an AP, PA, opposed beam, or post beam geometry. You get little cavities of high dose followed by low dose valleys within the tumor. That talk was amazing because we saw many cases where this very large tumor upwards of 1600 cc’s go all the way down to 600 cc’s, a 1000 cc decrease after a few fractions. So I think it’s really great.
I would say is when you’re getting into it, make sure that everyone’s on board and knows what you’re expecting. What protocol are you going to use? Are you going to use Cerebin blocks? Are you going to use MLC based, lattice? We use lattice on the treatments that we did here at our clinic. And most of the discussion was where to place the spheres and how far away to place those spheres from each other, whether they’re on an axial plane or other planes, sup/inf and left/rt from the GTV. So sphere placement is really one of the bigger discussions, how you’re going to tackle that, what you’re going to do about partial spheres that may fall on the outside of the GTV. Are you going to treat those? Or are you just going to go with full spheres? As far as the planning, we focused on replicating the DVH from the paper. So again, that goes from your knowledge. I didn’t know really how to plan this, hadn’t planned one, but used my base knowledge of how to manipulate a DVH and how to create dose in the optimizer and with geometry. We can replicate anything that is in any paper with those skills. I looked at the paper, and I figured out how to replicate the DVH. From there, you need to figure out the proper geometry in order to deliver that DVH. The main goal is to create those peaks and valleys. For the dose profile along the beam path, what you’re looking for is that it looks like the end of a cone, and the tops of the cone are those high dose profile those high dose peaks and the bottom of the cone where that next prong starts is where that low dose is so you want to control the dose between those spheres to make sure that you have dose escalating inside the sphere and then low dose surrounding it. So you get both of those biological cell killing effects.
What’s your biggest advice on how to control hot spots?
That’s a very broad question and you can do it multiple ways. Let’s say you’re using target autocrop and you’re in Eclipse. So this will be from an Eclipse standpoint. If I’m using target autocrop, I’m going to control my hotspots up front with my upper objectives on my targets. Let’s just say something was 60 gray, 50 gray, 40 gray. Not something that is like a typical dose standard, but just for explanation purposes, let’s say those are the dose levels. It’s SIB and I’m using target autocrop. I’m going to put on the 60, I’m going to put a lower objective of somewhere around 60-50 and upper objective around 60-100 or 60-90. Very tight.
So what that says is my 60 is going to be here and my high dose is going to be right there, 6090, 6100. So if I say 6200 or 6300, then my DVH just starts getting more diagonal. I want it to be straight up and down. So I’m going to give it a low dose minimum objective where I want the optimizer to cover the target, and I’m going to cap it off at the lowest dose I can in order to control that hotspot. And if I find that I’m losing target, I’ll do that consecutively down those dose levels: 50-50, 50-100, 40-50, 40-100. And if I find that I’m losing target coverage between those two, let’s say the middle targets not getting all the dose or the the higher targets not getting all of its dose 100 to 95, I might loosen up that upper dose to maybe 61 50 or you know 61 75, but I’m going to keep it at a range of around 103 to 105 percent of the prescription per dose level, I don’t want it to go over that so if you’re in there and you’re at 60 gray and you give it an upper objective of 110% of 60 gray, then it’s not going to work on anything below 110%. It’s going to shoot for 110% and then maybe give you a little bit more, actually. It might come out 112 hot, 113 hot. So if you limit it up front at around 102 to 105% on the upper objective, and then make sure you’re maintaining coverage as you’re optimizing the plan and meeting the goals and sparing the OARs, then you will effectively control those hotspots. Now, let’s say we get through the plan, it’s still like 112 hot, and I’ve done all the ideals, plans, passing everything, it’s just hot, and I’ve used that same scenario that I just talked about. I may come in with converting an isodose cloud to a structure. If it’s 113 hot, I may look at it, and I’m talking about the max dose in the plan, and say, give me an isodose cloud, convert an isodose cloud of say 108% and then that will create a structure. Typically, all of that 108% should be in your 60-degree volume. It shouldn’t be outside of it. If it was, then you didn’t put something in the optimizer correctly because the automatic NTO does a very good job at keeping those dose levels separate. But let’s say it was hot there, and I created that isodose cloud, and then I’ll go back into the optimizer and put a max dose objective on that of say 105% of 60 gray on that 108% isodose cloud. I’ll give a relatively high priority knowing that I’m not going to ask for less than 60 gray. Never take that dose down below 60 gray because you want 60 gray to be delivered. But since it’s 108%, ask for the optimizer to knock that down to say 105% or 103%, 102% if it’s not working. But make sure you’re still maintaining target coverage. Let’s say that doesn’t work. You’ve tried it, doesn’t work. It’s still sitting at 110.5. I’m always continuing from previous and using intermediate dose from the plan every time. So then, let’s say none of those worked. I’m coming back in and I’ll just put a body objective on it. I’ll pop the body on if it’s still 110.5% hot. I like my plans to be around 107 to 108; 105 would be ideal or less. But, you know, the 107 to 108 is a good range and achievable range for VMAT given the scenario. I’ll come in with that body objective and turn on the high dose, your highest dose level target while you’re in the optimizer. Turn that on and turn the body on, turn everything else off. You’ll see on the DVH curve in the optimizer, you’ll see that high dose come down and then you’ll see a little tail. And that little tail is just pixel dose, right? It doesn’t really need to be there. It’s not doing anything. So where that pixel dose is riding along with that body, I’ll drop an upper objective on that 0% volume and give it somewhere, I’ll start out at 200 priority. And this may fall in the 109%, 108% range, right, of 60 gray.
But I’m looking at that tail, I’ll drop that body constraint on there and just start escalating priority until I get what I want. That’s the last step, the last thing that I’ll do to control a hotspot if I need to if I haven’t done it in those other steps. And don’t be afraid to escalate that to say 999 priority. If it’s not working make sure you look at the cost function on your DVOs and make sure it’s working.If it’s at 0.0%, at 108% max dose, and at 200 priority, and it’s at 0.0%, then up the priority. Up it to 500. Look at the cost function. It may jump to 0.1, but your max dose didn’t go down. I’ve done this many times. It’s a technique that I like to utilize. So I’m not afraid to pop in 999 as a priority right off the bat. I know it’s pixel dose, and I know it’s not going to hurt my tumor coverage because it’s more than 100% of what I’m asking. So I know I’m not going to wreck the plan, but that’s just based off experience from what I’ve done, in prior plans. So I’ll just work on that tail at 999 and start pulling it back until I see that. That cost function jumped to about 0.1, 0.2% of the total cost. And I know it’s not really hurting my plan, but it is working on what I’m asking it for. And that’s how I would, you know, attack those hotspots in that scenario.
Thoughts on using 6FFF for whole breast, IMRT, DIBH? Is it faster for the breath hold but more peaked beam? Do you ever plan with extras greater than 15 cm? Thoughts on jaw tracking? Do you use autocrop?
Yes, I use autocrop. Jaw tracking, I’m always going to have that on. The only time you’re not going to have jaw tracking on may be in an SRS case. So when you’re doing small SRS lesions in the brain,
and you’re fitting to that PTV, you need to make sure that physics has commission. You need to know what physics has commissioned for their small field of symmetry. So if they’ve only done their small field of symmetry down to 2×2 cm jaw size, then you can’t fit because this has happened before. I’ve fit to the PTV, it goes down to like 1.5, 1.2 jaw size, but we’ve only commissioned 2×2. In that case, I would fit my MLCs to the PTV like I normally would with a 0 or 0.1 MLC leaf margin, and then I would set my jaws to what physics has commissioned, which is 2×2. In the optimizer, I would go in and turn off jaw tracking so the jaws don’t shrink in. That’s the only time that I would personally turn off jaw tracking. In every other scenario, I’m typically going to leave it on. Why leave on jaw tracking? Because it’s going to move to the closest or the most open MLC leaf edge and it’s going to eliminate interleaf leakage. It’s going to be better for the patient. You’re going to have cleaner plans. Greater than 15 cm jaw for a Varian machine.
The one out of 10 times that I did have a greater than 15 cm jaw was on a case where it was very, very large. And in the VMAT planning operations manual for versions 15.1 and up, up to 16, not 18, although it’s still the same in 18, it follows the same 15 cm leaf max leaf travel distance. So if you limit it to 15, you’re going to have the best chances for modulation and probably decreased hotspots because your MLCs are going to be able to close across the field. If you have something bigger, then that MLC can only travel as far as 15 cm, and then this is all going to be open. The MLCs can’t get there. So 15 cm, it allows them to cross along the field so they can modulate the entire aperture.
In the manual, it does state that anything above 18 cm you will visually see degradation in your modulation. So in theory, you could say 15 to 18 is your window. Don’t go above 18 if you don’t have to. I would never do it. I’ve never done it; stick in the 15 to 18, always try to do 15. So that’s going to give you the best modulation at 15 cm draw size, x draw size.
So the 6FFF beam for whole breast, IMRT, DIBH. You know, if it were a large case. Anytime you get near the edge of that profile on a peaked beam, you’ll end up modulating out that peak dose in the center to deliver across a field and make it homogenous which may be defeating the purpose of the 6FFF beam by modulating out that peak. It does have a higher dose rate upwards of 1200 mu per minute so that could help in a breath hold case. Obviously, we don’t want the patient to hold their breath for very long. So any chance we can do so, I would focus on minimizing MU. If it comes down to it and the MU is large, for most APBIs we’re delivering 6 Gy per fraction. It’s not going to be a one-to-one MU. So you’re going to have high MUs. You’re going to probably be around 1800 to 2500 MU for a case like that. Let’s say it’s breath hold. For an APBI that’s a smaller target, but if it were whole breast and you’re delivering six gray, in that case, you could argue a 6FFF beam for the speed since they’re holding their breath. But that is something that I would be talking to physics about, right? You can plan it, and it’ll probably give you a nice dose, but you should really be talking with physics to make sure that it makes sense to do. If you can achieve a similar result with similar MUs with a 6x beam, you may end up with lower MU since you’re not modulating at that peak. So I’d do a plan comparison. I would do a 6X beam and a 6FFF and if the 6FFF has less MU or the same MU as the 6X beam, and the dose looks good that would be something that you’d have to talk with your physics team about.
What is your favorite part of being a medical dosimetrist and what keeps you motivated?
So I would say my favorite part of being a medical dosimetrist is, and this might be a weird analogy to make, but it feels like I’m painting a picture.. When we put beams on a plan there are beam modulators that we can use in these plans to make it look nice. And there are techniques within the treatment planning system where we can literally paint dose. And we are kind of artists in that way. So my favorite part of being a medical dosimetrist would be the art of shaping dose. I really like getting those PTV volumes and making them look very tight and conformal and discreet. Seeing all the dose levels cut right where the PTV stops and the next one starts. That’s probably one of my favorite parts.
What keeps me motivated is knowing we play a huge role in the treatment plan for the patient. It starts with therapy providing a high-quality CT scan, then the doctor contributes their clinical knowledge and guidance. From there, it’s on us to create an effective plan that delivers the correct dose for the patient. So that definitely motivates me, knowing that I’ve given this patient the best possible plan that I can. Aside from that, what really keeps me motivated on a personal side would be the plan challenges.
It’s one thing to do really great in them, but it’s another thing to learn from what you could do better. So in a sense, that motivates me to push myself and better my skills to become better than I was yesterday. So that’s kind of my motivation is just continuing to get better. Those planned challenges help me get better.
My clinic has challenging cases too, so that that motivates me to try a new technique and see if I can do it better than I did the last time. The field keeps me motivated – rapid arc dynamic is an excellent technology that we’re going to be getting here in the future and that’s amazing. That’s an amazing feat that Varian has figured out to get that collimator to rotate dynamically. So the technology keeps me motivated to try all the new things that we get to try.
How hard was dosimetry school? Would you recommend master’s versus certificate?
Well, dosimetry school is hard. I’m not going to say it was easy, but it’s doable. I love dosimetry, I love learning about dosimetry. So for me, it was hard, but it was achievable because I had a passion for it.
And just personally, you can get either a bachelor’s or a master’s, both are going to be really the same base knowledge. It comes down to the clinic that you’re in and how well you perform in clinic, what you’re exposed to, and what you can do.
From a hiring perspective, I think a master’s looks better. But that doesn’t mean you’re better than the bachelor’s person. But it does make you look better on paper. Unfortunately, we all have to get past that resume selection. Amaster’s is going to look better, but I’m not saying that means they’re a better student. I went the master’s route just for that reason. I already had a bachelor’s, but if I didn’t, I think I would try to get the master’s in this field because it is becoming a little more saturated in a sense.
A master’s would help you in that scenario, but it doesn’t necessarily mean that at the end of the day, you’re going to be inferior by having a bachelor’s versus a master’s.
How many treatment plans do you need to make per day/per week?
You know, that ranges from five to 15, 20 a week, with 20 being the absolute max. It also ranges by the time of the year; it seems like at the end of the year, everyone’s coming into, or at the end of their insurance when it’ll renew the next year and they’ve already met the deductibles. As far as how many plans per day that’s that’s hard to guess off the top of my head, but I busy a lot and then it can taper off, though I’m overseeing CT, making sure we got good input, doing image fusions, contouring, doing the plan, getting it checked, maybe reworking the plan if I need to, and then just managing what’s on my plate and keeping things rolling. You don’t want to delay the patient, so just staying on top of your tasks and getting things done is critical.
Are you remote, on-site, or hybrid?
I’m hybrid, two days remote and three days on-site.
What do you enjoy the most about this position and what are some things that are more mundane?
I already touched on what I enjoy most, which is the problem-solving aspect. For me, the more routine tasks are things like image fusions and contouring, since they follow the same process. I wouldn’t call them boring, though. Contouring, for example, can actually feel meditative, even if some people see it as mundane. If your auto contouring goes down, it’s going to take you maybe an extra 30 minutes an hour depending on the case to contour something, but you can kind of get in the zone and contour. Maybe put some music on and it does in a sense become a little meditative because you’re focusing on what you need to do.
What are some things you wish you had known before or prepared better for in this field?
That’s a tough one for me because I did feel very prepared coming from X-ray. I already knew about radiation and built on that radiologic technology background. When I moved into therapy, I had a solid idea of what a dosimetrist did because I was interested and asked a lot of questions. If I hadn’t been so inquisitive, I would have wanted to learn more about what a dosimetrist actually does and why. But as a therapist, I already had a good sense of it.
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