Planning for HCC Radiation Segmentectomy: Mapping, Margins & Dosage

[Dr. Juan Gimenez]
High specific activity matters. We do believe that. The only way to do that is to treat as close to day-of calibration, which is on the same day as you can. The problem with that is with increased specific activity, your dose goes up too. Then you have to make sure that you minimize adverse events. The only way that you can minimize adverse events is by treating as small an amount of liver as possible to take care of the tumor. Otherwise, you're going to end up with a lot of specific activity, a high dose in a big volume.

That's what's been shown in all the studies like Target, for example. Beau has some articles too showing that it's about the size, the amount of normal liver that you treat that results in complications not necessarily the dose. When you put all of that together then you're basically left out as we need activity, we need dose, we've got to stay safe. The only way to achieve all those three is by getting as selective as you can. Then you have to go fish all these little vessels out to a point as to you've got to do all these things, your mapping has to take five hours.

We boil down our technique, literally – it's not ours. There's three papers that pretty much summarize everything that we do, and it's not my idea. Like I said, I'm not that smart, but I'm a great copycat. No, for real. One of them is Ran Gabas paper. There's an ACR Society of Nuclear Medicine consensus paper, and then there are the consensus guidelines for dosimetry where the most one updated one is from 2022. Basically, those three papers together are what we use.

Mapping is simple. If you just think of what the purpose of the mapping is then you can understand what it is that you need to do to get it right. Basically, the purpose of a map is to identify all tumor feeders, vessels that are going outside the liver, any potential extrapolate supply. With that being said, literally ours is a protocol. You have to-- always start by reviewing your imaging and try to identify any variant anatomy. Then stick to it. Power runs, heat. No matter how strong you are, you're not going to be able to inject five for thirty. You can't do that. Power runs. Start with the celiac. If needed, do an SMA and then go from big to small, either common or proper hepatic.

Do we do this for absolutely every treatment? No. If you only have left-sided tumors, yes, just into the left. If it's only right, right. If you somebody between segment IV or segment Va you have to interrogate both the left and the right because invariably you will have feeders from both.

Then cone beam. Cone-beam CT is the main state of our practice. Again, it's the same concept. Start big. Do a lower and then get smaller. Start getting selective and more selective until you make sure that you get what you need.

What people are going to say, Y90 don't work or have a residual. Wherever you deposit the radiation, it will kill that tissue. Whether it's liver, stomach, heart, esophagus, it doesn't matter. If it goes in there, you're going to end up with a hole. Whenever you have some leftover or some residual, it's not because the radiation didn't work. It's because you didn't put radiation there. That's why the concept of do a lower spin and then get smaller and make sure you have complete coverage is extremely important.

I will tell you, we use a lot of 2.0 French microcatheter so the liver -- a lot of times, we will not select those arteries you're mapping because they can get spasm or they can get dissected, and then you're not going to be able to treat. You have to be able to identify knowing that that will introduce an unknown at the time of delivery because you may have to spend a little bit of time but then identify everything. You may have bilobar disease, take the time to do it and just follow that big-to-small approach.

If you're on the right lobe, start with the right, come in on the right, anterior division, posterior division, Va, VI, VII, and cone-beam, all of those things, and get smaller. Then, I would say, take your time to look and be very objective about the images. Don't let your ego get in the way. That's how you end up missing things. I would say, take the time to write a mapping even when you have to select and interrogate a lot of vessels. If you do it that way, it will take you at most two hours.

Now, when a mapping takes four to five hours, and when you do the complete opposite, so when you say, "Oh, that solution is segment II. I'm going to go to segment II," and then you don't see anything. Then you start backtracking and backtracking and basically, you end up higher radiation doses, more time, more spins, more of everything. Start big and go small. It saves you time, literally. Everybody that comes through our practice, all of our trainees, that's how we tell them how to do it, and if you, ourselves included, deviate from that, we pay the price for it.

Then just come up with a treatment plan. Do it all at once and then decide. If you know that you have to treat four or five vessels, sometimes, yes, it'll be easy. That can take you about an hour. If you're sub-selecting multiple tiny branches, two of French, very tortuous anatomy, divide it. Just do two at a time. Don't get mentally exhausted and then give up. Just do two, bring them back two weeks later, do the other two, and then just get your imaging. We've learned from our own mistakes to say that our technique has evolved significantly since we first started doing this.

As of today, I can tell you that's what works best for us, and that's what's allowed us to replicate the results of, so like Tyler likes to call them the Y90 giants and I agree with him, all of these guys, but it's just having-- being very methodical and paying a lot of attention to detail.

[Dr. Chris Beck]
There's a lot of questions that I wanted to dig in on that. One of the things that strikes me is complete coverage of tumor. If you're going and sub-selecting each vessel, the way I think about it like on ablation is you want to hit the tumor. You also want to hit the margins around the tumor. Is that a consideration whenever you're treating?

[Dr. Juan Gimenez]
Yes, you'll always have a margin. Unlike, I would say, ablation, which you can get very just a tumor when you ablate that space if you want, if you think of vascular territories there, you're always going to be angiosomes-- that's a term Beau likes to use-- and triangular in shape. You're always going to have a little bit of a margin. We see the biggest issue is you miss part of the tumor and so–

I'm not talking about a centimeter. It's a couple of millimeters. That's where the lobar cone-beam is so important because on that lobar cone-beam it has multiple thing. You can see the entire enhancement, part of that tumor. If you get too selective and you miss something, also, if you do a right lobar and you didn't see complete enhancement, that you may have to go to the left or you have a phrenic or something else going in there that you have to look for, that's where the issue comes.

You're always going to get a margin no matter how selective you are, at least that's been our experience because there's always a little bit of normal tissue. The most important thing is the more selective you get you may just stop isolating other branches and maybe supply that you may miss. I can tell you, it's very easy to do if you just go straight to a vessel and you see a nice, round enhancement area like, "Oh, I got it all," and then you go look back and I'm like, "Oh, yes. I guess, I missed this little edge." That's it.

[Dr. Chris Beck]
We've talked about it in a roundabout way as far as you guys try and get selective as possible, high dose matters like as far as hitting 400 gray. Can you get a little bit more specific about when you're ordering your dose? You already know the volume that you're going to be treating, you want to minimize or keep the volumes as low as possible. When you're dosing these patients, you care necessarily if it's 500 gray, 600 gray, or you just try and pick a vial that is going to be above 400?

[Dr. Tyler Sandow]
Dead is dead.

[Dr. Juan Gimenez]
I would say our baseline is 400s. There's a little bit of caveats to that, but we've gone as high as over 1,000 gray to perfuse volumes and tumors. Granted, small volumes, putting 1,000 gray in a 300 to 400cc volume, that's dangerous. Small volumes, yes. The biggest caveat that we noticed that we try to be careful is close to a porta hepatis and that common bile duct because you may get some issues with the bile duct and then you end up with strictures and they need biliary drain. I would say close to the hilum, be a little bit careful. If you're peripheral, right there next to the gallbladder doesn't matter.

Tyler has a case, like you showed, so 1200 gray, segment V, right there next gallbladder, and nothing happened to it. We've done it next to the colon, next to the stomach. We have not seen any complications from the procedure itself. It's not an issue for transplant according to our transplant surgeon. We have been told sometimes if you're going to go to resection, not necessarily transplant, there may be some adhesions that may make the operation a bit more complex. We'll just say 400.

We do follow the dosing recommendations from the consensus guidelines. If you look through all of those, and most of this comes from a dosing sphere, they'll tell you that you need to put at least 205 to tumor, preferably 250 to 300. We try to follow that as our lower end of radiation. We cannot get that much into tumor, then we might have to switch to a different modality. Using 200, even close to that porta hepatis region has been safe for us.

[Dr. Chris Beck]
Does this mean everyone is Week 1, Wednesday, Thursday, Friday treatment, or virtually–

[Dr. Tyler Sandow]
Just about. Now, we will occasionally – if you're treating really small volumes like, let's say, if you're only treating 25 mLs worth of volume and you put in the smallest file size you can get as a 350q, and you're going to put that in 25 mLs worth of tissue, that's going to be close to – I'm trying to spitball. I think it's 1,200 gray. Now, talking to people, and you never know who you're talking to about this, 1,200 gray can make people nervous because they just associate gray with, "Oh, that's too hot. I'm going to cook my hands on it," or something. Granted, dead is dead. If it was going to be dead at 400, it's going to be dead at 1,200. Really, dead is dead.

I like to come back to that whenever we're talking about radiation delivery. Occasionally, rarely, we'll deviate into a Week 2 Monday, especially if it's a small volume and we want to keep our radiation in the porta hepatis region. We want to keep our actual gray low in the 250, 200 range. We'll deviate a little bit. I would say, again, 90% to 95% of our deliveries are in that Week one, Wednesday to Friday range.