Cyberknife vs. IMRT

[Thaiger75]

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Steph,

What is your feeling on the Cyberknife vs. IMRT for cranial and extracranial lesions?

 

[stephew]

Steph,

What is your feeling on the Cyberknife vs. IMRT for cranial and extracranial lesions?

Ive never worked on the cyber knife. I do know there are some localization issues. But remember tradiational imrt isn't "single shot" however it can be adapted to be so on linacs. Youve got your stereotactic IMRT, your dynamic IMRT (3D line). it gets confusing. Honestly? i suspect that the Great Eli Glatstein's comments hold up well here: that is, if radiation oncologists were trying to cure polio, right now we'd merely be developing more efficient Iron Lungs.

 

[cancer_doc]

Cyberknife is just a 6MV linac hooked up to a robotic arm. Unlike linac-based stereotactic, ST-IMRT, and such, it does not give you true 3-D conformal abilities- much like gammaknife.

I think linac-based ST is better, but more time and technically consuming than C-knife. However, it has better versality.

 

[stephew]

Cyberknife is just a 6MV linac hooked up to a robotic arm. Unlike linac-based stereotactic, ST-IMRT, and such, it does not give you true 3-D conformal abilities- much like gammaknife.

I think linac-based ST is better, but more time and technically consuming than C-knife. However, it has better versality.

I agree re: linac based ST; but you dont need noncoplanar treatment to make it conformal as heck. see tomotherapy (it rules!)

 

[kryptonite]

Cyberknife has a major advantage as it is frameless, allowing for sterotactic radiosurgery to non-CNS sites like lung and GI.

 

[pikachu]

I rotated at a center that was using cyberknife a lot. one of the problems they had was that there were some patients who could not tolerate lying on the table for the duration of treatment (> 1 hour). this was an issue esp. in people who had spinal metastases. This wasn't a HUGE problem but it did occur, although most people did well. Also, there was a certain amount of uncertainty in dosing especially in soft tissue sites.

 

[stephew]

well linac based works just as well.

 

[kryptonite]

At Stanford, where the cyberknife orginiated, I've never seen a problem w/ targeting w/ fiducial seeds.

And I don't believe that linac based radiosurgery allows treating non-CNS sites because it still requires a frame.

 

[stephew]

At Stanford, where the cyberknife orginiated, I've never seen a problem w/ targeting w/ fiducial seeds.

And I don't believe that linac based radiosurgery allows treating non-CNS sites because it still requires a frame.

incorrect. it most certainly does. We'll be doing it soon. See Varian triology.

 

[cdf95cro]

Concur w/ Steph-

I think Okunieff's folks do "extra-cranial IMRS" using a linac for lungs, and
San Antonio uses MiMic linac collimation w/ vacuum immobilization (no fiducials) for liver lesion radiosurgery.

Cool stuff.

 

[JTradonc]

I also heard that cyberknife does not generate therapeutic electrons.

 

[stephew]

I also heard that cyberknife does not generate therapeutic electrons.

i can't imagine why you'd want therapeutic electrons too often with something stereotactic.

 

[JTradonc]

You wouldn't want electrons for stereotactic. But, the cyberknife could be a useful tool for arc therapy if it did generate electrons. For example, at Univ of Utah, chest walls can be treated with dynamic electron arc therapy (pioneered at this institution). This eliminates the need for matching electron fields over large curved surfaces. We do it with a normal linac and MLC, so again, you don't need a cyberknife. It just might make things simpler.

 

[stephew]

You wouldn't want electrons for stereotactic. But, the cyberknife could be a useful tool for arc therapy if it did generate electrons. For example, at Univ of Utah, chest walls can be treated with dynamic electron arc therapy (pioneered at this institution). This eliminates the need for matching electron fields over large curved surfaces. We do it with a normal linac and MLC, so again, you don't need a cyberknife. It just might make things simpler.

yeah i dont think there is a big market/need for a stereotactic or arcing electron speciality device.

 

[jhissdav]

Regarding Cyberknife I assume that since beams can converge upon one another from many different directions and many focal points that nearly any pattern could be developed from the intersection and subsequent accumulation of dose from the various beams. Why would this not be considered conformal? Are my assumptions inaccurate?

 

[Thaiger75]

Regarding Cyberknife I assume that since beams can converge upon one another from many different directions and many focal points that nearly any pattern could be developed from the intersection and subsequent accumulation of dose from the various beams. Why would this not be considered conformal? Are my assumptions inaccurate?

CK IS conformal treatment and has the ability to deliver non-isocentric treatment via its freely mobile robotic arm.

 

[radoncmonkey]

Is SRS the same thing as Cyberknife? How is Gamma Knife different? Basic questions, but if I'm going into this field..I should kinda know so I don't look dumb, right?

 

[Gfunk6]

Gamma Knife and CyberKnife are both classified as stereotactic radiosurgery devices.

Gamma Knife uses 201 sources of Co 60. The patient's head is physically restrained using a head-frame device. The Cobalt beams are "shaped" using a collimator helmet for different sized lesions. GK is classically used to treat brain lesions of both benign and malignant nature. It has a more limited role in other parts of the head (e.g. savalge radiosurgery for nasopharyngeal cancer).

CyberKnife is essentially a small linear accelerator which is mounted on a robotic arm. Like GK it has various collimator sizes but there is only one beam, unlike GK. The treatment times tend to be long, sometimes two hours or more since it takes longer for the treatment to encompass a given target. CK uses image-guide localization which is semi-real time. Usually some type of fiducial marker is placed in or near the target. The CK then takes fluroscopic images every few minutes and is able to move to accomodate the target (e.g. lung mass moving w/ breathing). CK was originally designed for brain and spinal cord targets but its scope has expanded to full-body radiosurgery.

Both are clearly more complex, but that's the gist of it.

 

[IndyXRT]

Regarding Cyberknife I assume that since beams can converge upon one another from many different directions and many focal points that nearly any pattern could be developed from the intersection and subsequent accumulation of dose from the various beams. Why would this not be considered conformal? Are my assumptions inaccurate?

It's not that the treatment isn't conformal. It's that the machine can't be used to deliver traditional 3D conformal treatments, thus making it less versatile than things like the Trilogy.

 

[stephew]

Ive know much more about this now. It is conformal. its not Conformal. Meaning we use the phrase in two ways; conformal means just what it says. Capital "C" Conformal is a term that came about to distinguish new 3D CT based planning form older forms. Since then we've moved to even more elegant and conformal treatment with things like IMRT (though not always and its not always wanted!). To distinguish from older 3d Conformal, we give it new names such as IMRt or whatever the new technique is.

 

[stephew]

Gfunk indeed gives the gist of it. But there are many more issues as you specialize. GK is not as conformal as linac-based or cyberknife type treatments. Cyberknife is frameless ( as novalis and others can be). Dose rates are different, stability is difference. capacity and redundency issues between different modalities are very different.

GK's virtue is that its a dedicated device for intracranial Srs thus freeing patients from having to wait around for machine modification for tx after SRT treatments. But outside of that i dont think it has much to offer.

 

[radoncmonkey]

Ok, I get the difference between GK and cyberknife. But what is the difference between cyberknife and SRS? Are they the same thing, but cyberknife is just frameless, or?

 

[deleted4401]

CK is a type of SRS/SRT. I think if you use the term stereotactic radioSURGERY it is just one fraction, but if it is fractionated then officially you should say stereotactic radioTHERAPY. Kind of semantic ...

As far as linac-based SRS (Trilogy) for intracranial/extracranial lesions: because the gantry/couch/collimator would need to be re-positioned so often, are the treatment times much longer than a GK or CK treatment? Or is it because of thoroughput issues, that a clinic may dedicate its Trilogy for IMRT and have a CK for all SRS/SRT?

We just started using the new Leksell Perfexion GammaKnife. Much improved from the 4C ... Treatment times are shorter, almost no collisions, and the contouring software is pretty sophisticated.

-S

 

[stephew]

Ok, I get the difference between GK and cyberknife. But what is the difference between cyberknife and SRS? Are they the same thing, but cyberknife is just frameless, or?

cyberknife is a brand. Like gammaknife. its coke versus pepsi there are differences but its all cola. this is all srs. srs is cola and cyberknife is teh brand.

 

[clintpark]

cyberknife is a brand. Like gammaknife. its coke versus pepsi there are differences but its all cola. this is all srs. srs is cola and cyberknife is teh brand.

You may also hear the term Accuray a lot, which is the company that makes Cyberknife machines.

Analogies
Refrigeration: SRS, fractionated stereotactic RT (techniques or concepts, not machines)
Accuray, Leksell: Frigidaire
Cyberknife, Gamma Knife: PHS series
Perfexion (the newest generation in the Gamma Knife line): PHS69EHS

Also, I agree that the distinction between stereotactic radiosurgery and fractionated stereotactic radiotherapy that Simul made is somewhat semantic, but it may have much broader implications in the future. I would encourage everyone to use them "correctly."

When we treat a T1N0M0, stage IA lung cancer in 3 fractions, we (at UTSW) don't call it "extracranial stereotactic radiosurgery." Rather we call it "stereotactic body radiation therapy (SBRT)." Most of the time, we use a Linac for this, but we would continue to use the term SBRT even if we used our Cyberknife.

 

[stephew]

semantics are still being defined in the field and not even some radoncs know it well.

 

[Easterly]

With respect to Thaiger's initial question, CK vs IMRT: I don't believe that using something like the Trilogy to do SBRT would be considered IMRT. My impression is that you set all your beam angles and cinch fixed MLC up to the PTV. There's no sliding window or DMLC at all. I don't even think it's inversely planned. Correct me if I'm wrong. CK, OTOH, is certainly inversely planned and can be said to modulate intensity using nodes and beam angles, even though it has no DMLC, just a collimator. Also, CK is LINAC based too, even though it's a compact LINAC without a bending magnet.

Tomo is, obviously, IMRT. Steph, you say you can get a good dose profile without non-coplanar beams, but do you think Tomo's inability to do respiratory gating or tracking limits it as a SRS tool? Certainly the Timmerman data on medically inoperable early stage lung doesn't report any gating, just dampening with abdominal compression and some extra PTV sup and inf. If UTSW does the same even though he's got a CK now, he must really not think funky respiratory tracking the CK does is worth it.

 

[stephew]

Tomo is, obviously, IMRT. Steph, you say you can get a good dose profile without non-coplanar beams, but do you think Tomo's inability to do respiratory gating or tracking limits it as a SRS tool? Certainly the Timmerman data on medically inoperable early stage lung doesn't report any gating, just dampening with abdominal compression and some extra PTV sup and inf. If UTSW does the same even though he's got a CK now, he must really not think funky respiratory tracking the CK does is worth it.

its not an srs (true srs- single dose) tool now, correct. tomo has plans to evolve its technology just as the others do and we'll see how this goes. I wouldnt do intracranial srs either now.

 

[clintpark]

With respect to Thaiger's initial question, CK vs IMRT: I don't believe that using something like the Trilogy to do SBRT would be considered IMRT. My impression is that you set all your beam angles and cinch fixed MLC up to the PTV. There's no sliding window or DMLC at all. I don't even think it's inversely planned. Correct me if I'm wrong. CK, OTOH, is certainly inversely planned and can be said to modulate intensity using nodes and beam angles, even though it has no DMLC, just a collimator. Also, CK is LINAC based too, even though it's a compact LINAC without a bending magnet.

Tomo is, obviously, IMRT. Steph, you say you can get a good dose profile without non-coplanar beams, but do you think Tomo's inability to do respiratory gating or tracking limits it as a SRS tool? Certainly the Timmerman data on medically inoperable early stage lung doesn't report any gating, just dampening with abdominal compression and some extra PTV sup and inf. If UTSW does the same even though he's got a CK now, he must really not think funky respiratory tracking the CK does is worth it.

I don't think there is anyone out there that thinks the SBRT Dr. Timmerman does for medically inoperable early stage lung cancer should be considered IMRT. We certainly don't. Your impression about fixed beam angles, tight margins, no segmentation, no inverse planning are all correct. I would also add inhomogenous dose distribution within the PTV, rapid dose falloff, and most importantly, a large dose per fraction are what characterize SBRT.

You are also correct in stating that we do most of our SBRT on our Trilogy and Synergy S machines with abdominal compression, without gating or tracking. Our interfraction position verification is done with daily cone beam CT. Intrafraction motion is measured (guessed at...) by another cone beam CT at the end.

 

[G'ville Nole]

You are also correct in stating that we do most of our SBRT on our Trilogy and Synergy S machines with abdominal compression, without gating or tracking. Our interfraction position verification is done with daily cone beam CT. Intrafraction motion is measured (guessed at...) by another cone beam CT at the end.

Clint, just curious about the treatment planning process there. Do y'all use motion corrected GTV volumes (slow-CT or 4D-CT) at all, and is there a CTV expansion prior to PTV expansion?

 

[clintpark]

Clint, just curious about the treatment planning process there. Do y'all use motion corrected GTV volumes (slow-CT or 4D-CT) at all, and is there a CTV expansion prior to PTV expansion?

We do 4D CTs for all lung planning. We use a plain CT for GTV volume and planning, but also use MIP for ITV volume. The ITV volume + a small margin is used for PTV. There is no separate CTV expansion. For daily verification (for SBRT), a cone beam CT tumor volume is compared to ITV.

 

[Isodose]

Had to join in on this discussion as this is the part about Rad Onc I love the most. I've been a long-time browser of the forums. Currently a resident in Rad Onc.

We do a lot of SBRT. Primarily we treat definitive lung, oligomets, more and more livers for HCC, some spine mets and are working on a protocol for unresectable renal cell. We use the bodyfix double vacuum imobilization system. All lung and liver patients get 4D-CT. Our primary lung contours are: MinIP ITV, MIP/ITV and FB with a 0.5cm symmetrical expansion for PTV. We utilize abdominal compression selectively. The goal with the MinIP contour is to create a very inhomogeneous dose distribution within the PTV and really push the dose up in this area. Intensity modulated SBRT allows for this very nicely.

SBRT can be delivered with IMRT or without, depending on tumor location. The primary defining point making a treatment course SBRT is 5 fractions or fewer with SBRS being delivered in a single fraction (we do this rarely). Cases that use IMRT use 10-12 static modulated beams. Without we either use static shaped beams or dynamic conformal arcs.

All patients get daily pre-treatment 4D-CT on simulator. After image registration, patient is moved in the Bodyfix to Trilogy table. CBCT is performed and required shifts performed prior to treatment.

We currently have 2 Trilogies for this purpose and a 3rd coming in March with in-room mobile helical diagnostic-quality CT (CT-on-rails type setup).

We also utilize calypso IGRT for our prostate patients with dreams of many more applications to come, possibly for augmentation of our SBRT program.

Anyways, couldn't resist joining in on this one. Take care.