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Procedure Guide: Cryoablation for Painful Bone Metastases

Author Sara Stewart covers Procedure Guide: Cryoablation for Painful Bone Metastases on BackTable MSK

Sara Stewart • May 28, 2024 • 36 hits

Cryoablation for painful bone metastases is a multifaceted procedure requiring careful consideration of sedation, imaging guidance, neuroprotection, and interdisciplinary collaboration. This article compares imaging modalities such as cone beam CT, ultrasound, and hybrid angio-CT; and details the selection of Boston Scientific's IceFORCE and IcePEARL probes, highlighting their suitability for different tumor sizes and locations. The article also emphasizes the importance of neuroprotection, discussing hydrodissection and carbodissection techniques to safeguard critical structures.

This article features excerpts from the BackTable MSK Podcast. We’ve provided the highlight reel in this article, and you can listen to the full podcast below.

The BackTable MSK Brief

• Effective cryoablation for painful bone metastases requires careful planning, including considerations for sedation. General anesthesia is often preferred for longer procedures to ensure patient comfort and immobilization.

• The selection of imaging modalities, such as cone beam CT, ultrasound, and hybrid angio-CT is critical and should be based on the procedure's complexity, anatomical location, neuroprotection technique used, and interdisciplinary team involvement.

• Choosing the appropriate cryoablation probe, such as Boston Scientific's IceFORCE or IcePEARL, is dependent on tumor size and location. IceFORCE is suited for larger tumors with its larger ablation zone, while IcePEARL is ideal for smaller, more superficial lesions.

• Neuroprotection techniques like hydrodissection and carbodissection are an important part of any cryoablation procedure. Both hydrodissection and carbodissection can protect neural structures from thermal injury, but hydrodissection is more compatible with ultrasound.

A Procedural Guide to Cryoablation for Painful Bone Metastases

Table of Contents

(1) Step-by-Step Guide to Setting Up Your Cryoablation Case

(2) Choosing the Right Probe for Cryoablation

(3) Cryoablation Neuroprotection Techniques

Step-by-Step Guide to Setting Up Your Cryoablation Case

When preparing for cryoablation of painful bone metastases, several critical factors must be considered, including sedation, imaging guidance, and the presence of interdisciplinary team members. General anesthesia is often preferred for longer procedures. Imaging options such as cone beam CT, ultrasound, and hybrid angio-CT are selected based on the procedure's location and complexity; however, ultrasound may be less effective with CO2, making hydrodissection a preferred alternative in such cases. The electrophysiology team is frequently involved to monitor evoked motor potentials, necessitating that the patient remains unparalyzed. When concurrent interventions by vascular surgery are required, hybrid angio-CT systems may provide advantages.

[Dr. Jacob Fleming]
Talking about the imaging guidance on this case, I know you're a big CT proponent and using ultrasound as well in some cases here. Just tell us about your procedure suite for a typical cryoablation case for a MET case. What's sort of the setup like? Do you always have the ultrasound ready to go and patient that you alluded to usually being under sedation and just the setup the day of?

[Dr. Jack Jennings]
Depending on the case, longer cases, I pretty much will always do GA these days. Predominantly with cryo CT guidance so I can see or cone-beam CT, the problem is, well, you can see this is not as great a CT as my procedural CT. Ultrasound, I've got to make a decision. If I'm close to the skin and want to use ultrasound, then I can't use CO2 because obviously that's gas/CO2/air doesn't equal good ultrasound. Where I will use ultrasound over CO2 are in the extremities, some of these feet, whether it's neuromas or we had a sarcoma there recently where I'm getting really close to the skin.

Then I'll forego the CO2 and just do hydro dissection and then I put the ultrasound probe because then the hypoechoic ice ball going close to the skin. I'm a big proponent of not so much, not always in these cases, but for biopsy cases and all these, I've got the ultrasound in the CT room, like a proponent of doing both. Francois Cornelis, he will do some of these rib cryos with ultrasound, which I think is pretty cool. I don't, but Francois has some nice pictures of those. Surely ribs, if you're out on the fluffy side and you don't have a lot of ribs, ultrasound cryo for bone, so it's bone, would be just fine because he sets it right up next to the bone and also you can see the ice ball growing towards the skin.

Then in the room, you've got the electrophysiology people. It's a crowded room. Then you got the anesthesia people. Occasionally I can convince them to do MAC, which patients are always appreciative of, but the ones that are going to be three hours long, it's not unreasonable just to do GA. Then if they're obviously with evoked potentials, they can't paralyze them because you're evoking motor potentials, so A, they can't do the paralyzing.

Then, we don't have one yet, which we're going to in the new tower, the CT on rails or the combined hybrid, which maybe that's how we'll get our old friend Doug getting into 2023. We'll have to get one of those. That's having a sole fluoroscopic fellowship. There are benefits of both, and there's nothing. I was trained by Lou Galula, so I'm very fluoro-trained. I like comb beam. It's just comb beam to get those spins is not where-- there are newer units that are coming out for sure that are much better. That's where those hybrid units with the CT on rails offer the best of both worlds.

[Dr. Jacob Fleming]
Absolutely. I agree with that. I have a lot of envy for those systems, gotten to use a couple times, but I'll tell you there's nothing more frustrating than being ready to take a spin and then the machine starts telling you “does not compute, does not compute” because of the positioning or whatever.

[Dr. Jack Jennings]
It's hitting the drape, oh my gosh.

[Dr. Jacob Fleming]
I'm sure everyone listening to this has had that experience at some point. Again, cone-beam CT is super versatile, has so many uses. The hybrid angio-CT approach, I think it really works particularly well in a lot of these situations, especially in maybe some of the more complex ones where our vascular colleagues might be doing an embolization of like an RCC MET first. Of course, you really need that multimodality.

Listen to the Full Podcast

The MOTION Study: Cryoablation for Painful Bone Metastases with Dr. Jack Jennings on the BackTable MSK Podcast)
Ep 38 The MOTION Study: Cryoablation for Painful Bone Metastases with Dr. Jack Jennings
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Choosing the Right Probe for Cryoablation

Another essential aspect of planning a cryoablation procedure is selecting the appropriate probe. Boston Scientific offers two notable options: IceFORCE and IcePEARL, each with distinct advantages and limitations. The IceFORCE probe, with its larger gauge needle, is advantageous for treating larger tumors due to its capacity to create a more extensive ablation zone. In contrast, the IcePEARL probe is smaller and generates a smaller ablation zone, making it more suitable for smaller or more superficial lesions. The choice of probe depends on the size and location of the lesion, as well as the desired ablation characteristics. Additionally, cryoablation's ability to precisely control the ablation zone and maintain visualization of the ice ball enhances its effectiveness and safety.

[Dr. Jacob Fleming]
One thing in regards to the size of the lesions that this brings up, and you mentioned a moment ago, is the sculpting techniques with making your lesions. This is something I find really fascinating with cryo. Also from a planning standpoint, it definitely presents a bit of a cerebral challenge. I was just wondering, could you just tell us about your general approach with choosing the number and the type of probes that you're going to do? There are a lot of different kinds of probes, IceFORCE, ICEfx, and so on and so forth. How do you go about choosing from the quiver what you're going to be using?

[Dr. Jack Jennings]
I'm an IceFORCE man, if you were going to talk Boston, it's a bigger gauge needle. The beauty is you can dial it down. 100% equals 100% of the time, the gases are either at 5,000, 3,000 PSI. Then if you dial it down, that's basically, okay, so 70% means 7 out of 10 seconds, it's on. You don't do percent gas, it doesn't work that way for the jewel tops. My point being is, except yesterday, I did a desmoid that was, people must think I only do desmoids, but I will tell you, it was six centimeters cranial-caudal by like two and a half centimeters.

I use the IcePearl. Again, it's a 2.1, so it's a bigger, and we did, I think it was a four-probe case, but I like the IceFORCE. I feel like with any of them, I can dial down, but I do use all of them. It's just nice and tougher tissue to use, that bigger gauge needle. That's the other beautiful thing with cryo is it covers a multitude of sins. You're a fellow. We got fellows, and there's nothing more than attendings love to blame everything on the fellows, but you got less than "ideal needle placement". I don't get too bent out of shape. Now you keep to some rules, the bigger ices can be about two centimeters away.

The smaller probes, meaning the smaller size ice balls, you want to be about 1.5 centimeters away and that's for both companies. That's a principle. As long as you stay with that, you'll see it. I'll go past the 10 minutes. They used to tell you at 10 minutes, it doesn't get bigger. That's a bunch of nonsense. I'll sometimes carry out the 15 minutes when you're seeing the ice ball grow and never had an issue with it. It's the visualization and knowing the planning is coverage, keeping those rules of the 2 or 20 millimeters, 15 millimeters distance, and just letting the ice work for you. It's very nice. It's not impedance-based. We don't have to worry about that. What you do have to worry about, it does blow through a cortex.

Cryoablation Neuroprotection Techniques

Neuroprotection is crucial in cryoablation procedures, with techniques such as hydrodissection and carbodissection commonly employed. Hydrodissection involves the injection of a fluid, often a contrast solution mixed with D5W, to create a protective buffer around critical structures. This method enhances visualization and helps displace tissues away from the ablation zone, making it suitable for areas close to nerves. Conversely, carbodissection may be preferred when a gaseous medium is advantageous, particularly in regions requiring larger separations like the abdomen or thorax. The choice between these techniques depends on the anatomical location, the proximity of critical structures, and the specific procedural requirements.

[Dr. Jacob Fleming]
Of course, you mentioned already something we talked about quite at length in our last discussion, which is these neuroprotective techniques. Just for folks who haven't listened to our prior episode, could you tell us just a little bit about the CO2 dissection and hydro dissection techniques that you do under CT?

[Dr. Jack Jennings]
Sure. I did it just yesterday. I saw the patient early this morning. She's doing well. This was a rectus abdominis lesion. Bowel is the issue there. If you're doing it as a vertebral body or posterior element, obviously it's the spinal cord and actually nerve roots. Then if you're in the pelvis, sciatic, femoral nerve, all those. We have passive thermal protection. What is that? That's where I'll bring out the evoke potentials, motor and somatosensory evoke potentials to look for dropout and decrease amplitude and increase-- They've got to give increased wattage to stimulate the nerve. We do that. That's passive.

We can put a thermocouple to measure temperatures. Then active is what you were alluding to in the sense of we can do hydrodissection. Yesterday, we used 0.5 mls of contrast per 10 mls of D5W and basically in the peritoneal cavity injecting. Then we did CO2. Now, the CO2 didn't go where I wanted it to. That's why you got to see what it's going to do. Basically with that contrast solution, we created, so the bowel was up against, she was not a real big person.

The bowel was up against the abdominal wall, and obviously you don't want to cryo that. We displaced it and you can see with the contrast. Then with the contrast, you can see the ice ball extending into that contrast so you know your gap. We do it for the skin as well. We do it epidural. I'll use contrast intrathecally like a myelogram. Then I can see the ice ball extending into the canal and also for displacement. As was the case yesterday, I spent longer doing that than putting down the probes, but you're not doing them a great favor.

You treat the lesion. Now, they come out with a new nerve injury. Those of us who've done this a lot have surely had that happen, not purposely. I pull out all the stops, and as CO2 in the spine, typically once you get above mid-thoracic because it goes up in the noggin, we don't like to use it. We use the hydro or cooling. With heat-based, I'll use D5W, slow push cooling in the epidural space. Then I use evoke potentials anywhere I'm worried about nerves, which obviously means they'll have to be under GA.

[Dr. Jacob Fleming]
For the actual needles, getting a little bit into the nitty gritty, the needles you use for a hydro dissection or a pneumo dissection, you're using like a 22 gauge, 18 gauge, 2E in the epidural space and just tell us a little bit about that.

[Dr. Jack Jennings]
Yes. If it's non-cryo, a 22 is just fine. For cryo, I use 18 gauge because they will freeze up because a lot of times your needles are close to where the ice fall, and that happened actually yesterday. We had a little plug we had to pop out because we were one of the 18 gauge is right there. Cryo, mostly 18 gauge spinal needles and then microwave or RF, I just use a 22 because it's easier, but I'm not worried about it freezing up, but you will see that with cryo. Just remember no saline with the RF because it creates a plasma field this year. Use that D5W when you're using RF, just to be safe.

[Dr. Jacob Fleming]
We don't need more plasma than necessary in our cases. Yes, so that's good.

[Dr. Jack Jennings]
Just your ablation zone gets a little not predictable, right?

Podcast Contributors

Dr. Jack Jennings discusses The MOTION Study: Cryoablation for Painful Bone Metastases on the BackTable 38 Podcast

Dr. Jack Jennings

Dr. Jack Jennings is an inteventional radiologist with Washington University Physicians in St. Louis, Missouri.

Dr. Jacob Fleming discusses The MOTION Study: Cryoablation for Painful Bone Metastases on the BackTable 38 Podcast

Dr. Jacob Fleming

Dr. Jacob Fleming is a diagnostic radiology resident and future MSK interventional radiologist in Dallas, Texas.

Cite This Podcast

BackTable, LLC (Producer). (2024, January 5). Ep. 38 – The MOTION Study: Cryoablation for Painful Bone Metastases [Audio podcast]. Retrieved from https://www.backtable.com

Disclaimer: The Materials available on BackTable.com are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.

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