Clinical Benefits Using MapRT for Extracranial Non-Coplanar Treatment Planning – Implementation in Clinical Routine and First Results

Kirsten Hierholz (00:00):

Talk about our way to use MapRT in the routine and show you some first results of our planning. So these are my disclosures, and this is what I want to show you. So first of all, I would like to show you how we use MapRT. So I will not show you how MapRT is working because I think you’ve seen that already. Just to show you what we are doing and how we are using it. So we do some capture for every patient during our CT process. We decide later on whether we use this capture or not, just to be sure to have the capture. And then we are going to do a coplanar plan for every for all our patients. Maybe you have to know we are a small department. We have just two Linux and we have not been used to do non coplanar treatments.

Kirsten Hierholz (01:04):

So with the hyper arc system, we do this for SRS treatments, but normally, we don’t do non-coplanar treatments. So we had to start this. And so we do a coplanar plan because we know how good a coplanar plan can be. And then we have a look at the non-coplanar. And as soon as we have the coplanar plan, we will send this plan to MapRT because we decided to use a special isocenter and then have a look at the collision map and what are the possibilities we can do for this non-coplanar treatment. And it is important to know that when we have done this, we start doing a non-coplanar plan and by doing that, we know that there will not be any collision. So we don’t have to decide whether to use this couch deflection or another one.

Kirsten Hierholz (02:09):

We know if we use this couch reflection, the plan will, okay, we’ll be okay. And we sent the plan after finishing again to MapRT just to see if there is a problem during the transition between one and two fields. What is also important, we use four centimeters patient and couch buffer. At the moment you’ve seen Adi, they use two centimeters, but we are a little bit scared. So we decided the first time to use the four centimeters because if you go to the LINAC and have a look at the distances, if you have the four centimeters, you see this is really close between the patient and the couch or the couch and the gantry. And if you look from the outside, you will not be able to decide whether there will be a collision or not. And this is why we thought, as long as it is a better version, we still do four three four centimeters to be sure there will not be any problem.

Kirsten Hierholz (03:14):

So, which advantages do we see in those distributions? I would like to show you some of my, of our cases. We’ve calculated a lot of plans. We did not treat every patient with non-coplanar. Not all these cases have been treated, but I think they are impressive. So this is the dose distribution for an SBRT case of the lung. In that patient we did not treat with DIBH because patient was not able to do that. And here you can see very well that the dose distribution here we have a relatively big dose for the coplanar plan in, in the ribs and in the chest wall. Maybe I have to tell you that for all these slices coming now, we always have on the left side the coplanar on the right side, the non-coplanar case, and you always have the fields we use on the buff, and also you have the prescription dose.

Kirsten Hierholz (04:26):

So using the non-coplanar case, you see there is a reduction of the dose in the ribs. And if we have a look on the DVH, we see it’s really a big reduction of the dose to the ribs. So we are not so interested in the reduction of the dose overall, but we are interested in the DMAX for the ribs and looking at that. We see that we can reach the goal for the non-coplanar plan, but not for the coplanar. And also we don’t have more dose on the lung in that case. Another lung SBRT case. In this case, we used VMAT fields because we want to, we were able to do the DIBH, and you see that we have the bronchus nearby. So we wanted to spare the bronchus. And what you can see very well is that also the dose of, I think this is the 10 K ISO dose is reduced very good with the non-coplanar case. This means we have a much steeper dose gradient with the non-coplanar cases, which means we can reduce the dose on the lung. And having a look at the DVH, you can see it’s not too much what we achieved in that case for the bronchus. But we had a problem with the heart in the coplanar plan. We could not reach the DMAC values we wanted to have, but with the non-coplanar plan, we could.

Kirsten Hierholz (06:08):

This is a patient we’ve been treating for several mets in the lung of fatuma. And this patient, he was pretreated; this is the magenta structure you see here and also the spinal cord was pretreated. so we had to spare these areas, and also we wanted to treat the patient in this area. Some slices further after we’ve been treating this PTV, so we don’t want it to have any dose in this part. And you see with some non-coplanar treatment fields, again, we have a shrinking of the 10 gray ISO dose, and we could spare the pretreated area. And if you have a look on the DVH, you see again it’s very good to reduce the dose to the pretreated area and for the spinal cord, we have been asked by our oncologist to reduce the dose to at least eight grade because of the pretreatment of the spinal cord.

Kirsten Hierholz (07:14):

And this was also not possible with the coplanar plan. Then we wanted to see if we can also use non-coplanar treatments for cases where we have many fractions, because in the beginning we started with SBRT and so far, esophagus we are very interested in reducing the dose to the heart. And there you can see with some more non-coplanar fields, it’s very good to reduce this dose. And here you can also see that in the DVH, the dose to the heart and also to the spleen, it is much reduced. So, I feel it’s always impressive how much reduction you can get with a non-co nerve field. But because normally if you do some different treatment plans and try to improve a plan, we can see that the DVH is a little bit better. But seeing something like that is not the normal way we see.

Kirsten Hierholz (08:18):

And this was a very interesting case with a very irregular PTV. It changed; it’s a form in every slice, and we had several organs at risk nearby, which we wanted to reduce the dose. And my colleague had really a lot of work with this coplanar plan. And this is the patient is treated with the coplanar plan because we did not have a map rt, but we’d tried to improve this plan later on just to see what is possible. And here again, you see for the heart it is very good. And if you look at the DVH, you see this is really impressive. How big is the reduction of the heart, and looking for all other organs at risk? You see we have a reduction. So, non coplanar really getting better, giving us better dose distributions. Also for head and neck cases, it’s a good idea to have a look for non-coplanar cases. Here’s a patient where we had the problem that for the, with very much fields it was not possible to treat this patient. So this plan on the left side was not treated. We used an IMRT case, but I also tried to do also non coplanar case in this patient. And you see that the dose distribution is much better for the eyes. And looking on the DBH, you see the dose is very well reduced for the eyes and also for the optic nerves.

Kirsten Hierholz (09:57):

And the last case I would like to show you is an adrenal-clamped patient. There we have ask for our oncologist to reduce the dose to the pancreatic region, which they have to be showing here. And you see also, again, the shrinking of the 10 gray iso’d dose, and we could reduce the dose to the pancreas. Also mean dose of the pancreas is used and dose to the kidney. We could also reduce having a look at, oh no, this is, the last one, prostate. We did not treat any prostate cases till now, but when we look at the studies, we see that treating the prostate with just four or five fractions, then I think we have to think about improving our plans also. So for the 35, 36 fractions we normally do for the prostate at the moment, we will not do this at the moment with non-coplanar cases, but if you have a look at the dose distribution, you see it’s a little bit better.

Kirsten Hierholz (11:06):

And here we have also some structures for the wall of the bladder and the wall of the rectum, which is near the PTV. And if you look on the DVH, so you see that the dose is reduced for the anterior rectum wall and posterior bladder wall and all the rectum dose itself is reduced with the non-coplanar planar. So I think, think as soon as we are going to do the prostate also with only some fractions, we have to improve also the technique which we use for the treatment. And this is something we saw without asking for that. So we did not try to; we did not give any constraint to the hips, but we could reduce the dose with the non-coplanar plans. But at the same time, you have a little bit more dose on the intestine.

Kirsten Hierholz (12:09):

So here I show you the conformity index for the lung SBRT cases we’ve been calculating. For those of you who don’t know the conformity index, I would like to introduce it a little bit. You see on the right side the PTV, and if the PTV is covered very well from the reference dose you want to deliver, and you don’t treat any healthy tissue, then the CI will be near one. And if you have a dose distribution like that, the CI will be less than one. And in our SBRT cases if you have a look at the CI we have here, the CI is normally used for mets in the brain, which are LIGO spheres. And for the SBRT cases we have here, they are not like sphere. So, they are very irregular. So you always have some healthy tissue. You are also treating, and this is why the, the index itself is not near one. But you see, we have an improvement with the non-coplanar treatment. And for the GI of the lung, this means the deviation between the 50% isodose and the reference isodose shows us how deep our dose distribute is our dose fall off. And there you can see for all the SBRT cases, we have been calculating that the non-coplanar case is much better than the coplanar case. There are only four cases where we could not improve the GI, and Intuit was less good.

Kirsten Hierholz (14:02):

This is overall cases. We find that the GI is a little bit better if you use the non-coplanar cases. And this is a little bit different to that what Adi told us in the morning, if I told you we did not have any experience with non-coplanar cases. And mostly we do the non-coplanar cases, giving some more fields to the coplanar cases. And this is why we have more monitor units. So this is one thing I would try when I’m at home, just to change the treatment to not give additional fields, but use just non-coplanar fields. Maybe then we can also reduce our monitor units, but still, it’s not too much, and in eclipse it’s, you have the possibility to reduce the monitor units, it’s just for you to know.

Kirsten Hierholz (15:04):

So after calculating lots of plans, we decided that we want to start with the patient treatment when the, with the non-coplanar patients, but we knew our TTS are not used to that also, all our medical physicist staff is not used to do that. So we had to decide how we are going to start with that treatment and we decided we do some papers for every patient. So normally we don’t have any paper in our institute, but that far we decided okay, we will have some paper one for the first treatment and one step by step instruction for the RGTs for them to know for this patient you have to do the dry run doing the couch tool, let’s say 15 degrees and you rotate the gantry from this point to this point because this is something they are not able to see if they open the plan on the Linac.

Kirsten Hierholz (16:08):

So I think this is very important for them to understand what they have to do also to feel safe to do that. And this is working very well since we do that. And so I want to show you some results we found during these treatments. And one of them is that the patient positioning is influencing the clearance map. This is, if you think about that, sure that this will be this is one patient we treated in April. And on the right side you see the plan we’ve been doing for this patient. And the patient came back with another lesion in July and it, you see, it was not possible to position him in the same manner because he had some problems with his left shoulder. So he didn’t, was not able to have the same position. And I’ve been reconstructing this plan we used in April on the new city, just to see how this will be possible to give the same treatment for this patient if the elbows are not in the same position? And you see, there will be a collision. So this is important for the RTTs to know that they have to care for the, for the positioning of the patient’s arms.

Kirsten Hierholz (17:39):

Also, another example is the same patient. It’s the first treatment, and we had a field where we had the couch on 270 degrees, and the couch rotate the RY rotated from here to here. And on the second treatment, we found this: the patient was not holding, had his hand in another position on the hand grip. This is the patient who has some aching in his shoulder. So he was not able to put this arm on the same position, but we realized that it may be that there may be a collision if we did not detect this. And on the same time, we realized that it’s a problem that we cannot see the black hand grips of our positioning aid. So we changed this and have now white hand grips which are have been seen or can be seen in the ct.

Kirsten Hierholz (18:47):

And so we will not have this problem again. Also, the positioning aid itself influences how much possibilities I have to do the treatment. So, in this case I’ve been looking for centrally located isocenter where we want to do a full arc. And with this positioning aid we have been using in the beginning it was, it is possible to rotate the couch for at least 10 degrees, still using the four centimeters between the patient and couch as a buffer. And so we changed this positioning aid, and for this positioning aid, the distance to the top of the couch is reduced, and it is possible to reduce the distance between the elbows. And so we have a little bit more space, and the more space we have, the better plans we can get.

Kirsten Hierholz (19:55):

And so I come to my summary, we have better plans in less time in plan calculation. I did not tell you this before. We have a problem if we in Eclipse, if we have a difficult plan. So we have to do several cycles of optimization and we found that if we have a non-coplanar plan, we are much faster. So sometimes it’s just one or two cycles for optimization and we have a very good plan. So, this is really the time we spare for the planning. We are sure that there will not be any collision, so we did not see any problem for all the plans we already treated. Treatment time was slightly longer till last week. So last week we started with doing the couch deflections from outside. The time before we went inside, turned the couch on.

Kirsten Hierholz (20:58):

So this means you need a little bit more time, but now it’s much smoother and the positioning of the patient and the positioning aids you use will influence your results and the next step. So one of these steps we already did, and I think we will also reduce the couch. I’ve written here to three centimeters, but when I see what the colleagues are doing, maybe we will also do two centimeters. I have to discuss this with my team, and I’m sure we have more freedom, we have better plans, and we will surely have better outcomes and fewer side effects for our patients. And I think that’s the most important thing we can achieve with changing a treatment technique. And so thank you for your interest.