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Calpedaler
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   Posted 8/17/2007 9:57 PM (GMT -8)    Quote This PostAlert An Admin About This Post.
There is a current exchange on the ANA board surrounding the accuracy of Varian's new Trilogy system vs. CK or GK. I had found a post on this board where both Drs Spunberg and Medbery had expressed that Trilogy's total accuracy was in the 2-3 mm range vs GK (usually in the 1-1.5 mm range) and CK (shown to be at the .89 mm level). I had shared this with the other board and got this response:

"Trilogy has only been out since 2004 or 2005, so there isn't as much data out there as I'd like, however my radiation doc was able to quote me some numbers. He said that the accuracy at that site is generally within .5 mm, which is comparible to GK (Trilogy does the one-shot deal as well as fsr). However, on a "test head" (probably on a cadaver head), the accuracy was .02 mm. That was one test, and I'm not sure if that's due to the capabilities of the machine or the skill of my radiation doc (or the fact that it was a cadaver head). I have a lot of respect for Dr Medbery, but I'm haven't read anything that says Trilogy accuracy is 2-3 mm. I wonder if that's for non-brain radiation treatment, with the image guided technology? ANs tend to stay put; they don't move around as we breathe, and that seems like it would be an easier target to hit."


Clearly, accuracy for all the machines is easier for a cranial target such as an AN than one located elsewhere in the body, but the claims given this patient by her doctor would seem to be vastly better than either CK or GK. A related post had a more general but equally interesting question about machine accuracy:

"One question I do have is how can anyone really tell how accurate a particular machine is, since MRI scans are not even 100% accurate in their measurements of the tumor? What verification is 100% reliable for any of the radiation treatment modalities? And how is that really measured?"





So, I guess there are two questions:

What is the accepted protocol that is followed to validate the total accuracy / error of a machine hitting a tumor within X mm?
Are there any clinical studies for Trilogy that really validate it's level of accuracy as there are for Gk or CK? Is it really that good or just manufacturer hype?

Thanks

Mark


CK for a 2 cm AN with Drs. Chang and Gibbs at Stanford, November 2001

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radsrus
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   Posted 8/18/2007 7:26 AM (GMT -8)    Quote This PostAlert An Admin About This Post.
I'm sitting in a lovely garden in Santa Fe with a slow internet connection, and this will require a longer answer. I will get you a better answer within the next day or two.


Clinton A. Medbery, III, M.D.
St. Anthony Hospital Cyberknife Center
(405) 272-7311
buddy@swrads.org or cmedbery@coxinet.net

Clinton A. Medbery, III, M.D.
Southwest Radiation Oncology
1011 N. Dewey Ave.
Oklahoma City, OK 73102

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Calpedaler
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   Posted 8/18/2007 9:30 AM (GMT -8)    Quote This PostAlert An Admin About This Post.
Thanks Dr Medbery,

If I was sitting in a garden in Santa Fe right now I wouldn't have even checked the board :-) Beautiful area, especially the first week in October when they have the hot air balloon festival down near Albuquerque.

Ariadne, it is my understanding that trilogy is Varian's version of a radiotherapy machine, so it "competes" in the same space as Novalis Brainlab, CK and GK for cranial tumors such as a AN and probably more against CK for the treatment of tumors elsewhere in the body. I believe each of these systems has their own proprietary software and I would be surprised that any of them could or even would be interested in using a competitors software.

Some folks don't consider accuracy a significant factor in choosing what they are treated with, but having talked with Dr. Chang and read Drs medbery and Spunberg's posts, I tend to think it is the most important. There will always be some "spillover" but I think the point of accuracy is to minimize it. I also think a lot of patients get confused with the numbers thrown at them by proponents of different systems , thus why I was looking for some more information to share back with the ANA board. I remember reading a post by Dr. Chang describing the difference in total accuracy between GK and CK to include the scan and frame error. I think that's what most people should be told , instead of just machine error or whatever other partial elements can be discussed.

Mark


CK for a 2 cm AN with Drs. Chang and Gibbs at Stanford, November 2001

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Calpedaler
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   Posted 8/18/2007 9:50 AM (GMT -8)    Quote This PostAlert An Admin About This Post.
Dr. Medbery,

after I left my last response I saw the following post over on the ANA board on the attributes of Trilogy

"I've read about trilogy and picked up this:

it's faster, can deliver more rads in less time in a smaller targeted dose area
it is said to produce less side effects
it can use image guidance in real time each day of treatment
it can target an area as small as a pencil point
it minimizes damage to healthy tissue

when used it can deliver all forms of external beam radiation including IMRT, IGRT, SBRT... etc.

it combines good things from linac, ck and gk .... but what I think i picked up is that it's faster, higher doses can be used, it is more accurate, and it can be used with conformal beams shaping it most closely to the tumour and giving less to surrounding tissues

it also has "respiratory gating" with the breathing of the patient....

if you want to google sites then simply type trilogy + radiation treatment and you will get lots.......


here is one of the many that i read.....
http://www.umm.edu/news/releases/trilogy.htm

W."


Lot of what I call "glittering generalities" here but what caught my eye was their reference to it containing the best of all the other systems ( CK, GK, Novalis, etc). Admittedly the link attached is a PR piece by a hospital but they obviously are suggesting that Trilogy is matches the rest and is "best of Breed"

Mark


CK for a 2 cm AN with Drs. Chang and Gibbs at Stanford, November 2001

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Steve G
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   Posted 8/18/2007 7:16 PM (GMT -8)    Quote This PostAlert An Admin About This Post.
Dr. Medbery, I have been in the ANA discussion Mark referred to. I would like to tack on two more questions for your long reply when you get back from your lovely garden in Sante Fe with the slow Internet connection.

1. Why does GK use 12 Gy, and CK use 18 Gy, and Trilogy use 50 Gy, or why does smaller doses mean you need a larger total?
2. Is there any evidence that 28 small doses on Trilogy has a different result than 3 medium doses on CK?


8mm x 7mm x 6mm AN, left side, diagnosed June 12, 2007, not yet treated.

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radsrus
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   Posted 8/19/2007 5:21 PM (GMT -8)    Quote This PostAlert An Admin About This Post.
All right, let us start from the top and work our way through this morass...and by the way, don't believe ANY hospital PR pieces.

THere are a number of factors that go into successful treatment of tumors, particularly small tumors near critical structures as is the case with acoustic neuromas. These include:

Tumor characteristics: size, shape, location, previoius treatment if any, etc. To the best of my knowledge, no one has invented a way for us to change these things prior to treatment, so we can assume that all systems fact the same obstacles.

Team characteristics: treatment philosophy, experience, knowledge etc. These factors are intertwined inextricably with the selection of treatment machine except in the centers such as Oklahoma, Baylor, Phoenix, and a few others that have access to Gk, Ck and other methods of treatment. In general, team experience is important only up to a point. That is, once a team gets sufficient early experience, only small gains come from additional experience, at least in terms of actually performing the treatment. That said, if you have a choice of two teams that have experience with multiple delivery systems and are in close proximity, choose the one that has treeated a lot of cases rather than just a very few.

Imaging characteristics: MRI is inherently less accurate than CT, and the accuracy is more dependent on proper machine maintenance and calibration. It is beyond the scope of this piece to talk about why, but please accept that it is true. That is not the reason that CK uses the CT dataset for targeting, but it does produce a slight advantage. Data from Accuray suggests that if you use the best fusion package available to fuse CT and MRI datasets, there will be about a 0.5 mm difference. This is one reason we insist on CT cisternograms whenever we are really worried about critical structures around the base of the brain (brainstem, cranial nerves etc)

Machine characteristics: accuracy is only part of the issue. FIrst of all, if any radiation oncologist has a machine of any type that is accurate to 0.02mm and can measure that accuracy, he needs to be reporting it. That is simply untrue. Even Varian does not claim that. They claim a best case scenario of 0.5 mm accuracy in the three cardinal axes (x,y,z) and 0.7 mm when you include rotational accuracy. To that you must add imaging inaccuracy meaning that under the most perfect of conditions you may be able to get to somewhere around 1.2 mm. As you might guess, perfect conditions are rarely achieved in clinical practice. Second, any claim that Trilogy images during treatment is simply untrue. It images before treatment, or perhaps before every arc. Third, there is the issue of solid angle. Imagine the head of the CK traveling around not he surface of a large invisible sphere centered around the patient's tumor. The more of that sphere is available, the more angles from which the planning system can choose beams in order to avoid critical structures. Even the CK cannot use the entire sphrere (we are unable to treat the patient from directly underneat for instance), but we use a VERY large fraction of the sphere, and therefore have a better chance of treating the tumor and avoiding things such as the brainstem, cochlea, etc. Fourth, there is the issue of isocentric treatment versus non-isocentric. With isocentric treatment, you aim a number of beams at a particular point in the tumor. With Trilogy, you use beam arcs, and the entire arc is aimed at that same isocenter, and you simply have to live with any adverse effects. With CK, treatment is non-isocentric. This means that you can aim anywhere that is best in order to achieve the desired result. You may use a small number of isocenters with Trilogy, but CK directs beams from 100-300 or more directions that can come from anywhere and go anywhere.

Some statements in this thread are true:
Trilogy can deliver a higher dose rate (up to 1000 mu/min in stereotactic mode) than CK (400 mu/min on G3 machines, 600 mu/min for g$ machines. Henry Kissinger once famously told the chief Vietnamese negotiator at the Paris peace talks "You never beat us on the field of battle". THe Vietnamese responded, " That is true. It is also irrelevant." Dose rate is irrelevant.

Trilogy has respiratory gating. CK does not because it is unnecessary. Rather than use a gating technique that has been shown in studies at MD Anderson to be little better than no gating, CK actually images and tracks a tumor during respiration, making it unnecessary to turn the beam off and on during the respiratory cycle.

Trilogy can do several things: true, but do you want treatment with a machine that is being used 95% of the time to treat lung and breast and prostate, where stereotactic treatments are an afterthought? Or do you want treatment by a machine that is dedicated to your type of problem. Here's an interesting exercise: tell the Trilogy folks that you would prefer to be treated at 9:30 in the morning and see their response. They will not want to interrupt their busy day with your treatment in all probability.

The rest of the statements are all fluff and nonsense.

As for doses, GK uses 12 GY in a single fraction, we use 18-21 Gy in three fractins, and higher total doses are used by units treating with small daily fractions. The GK and CK treatments are probably nearly identical, the other possibly so as well. When you give a higher daily dose, you give a lower total dose.

There is not published Trilogy data on AN's of which I am aware. Older data from accelerators adopted to stereotactic treatment showed good 9but perhaps lower) control but higher complication rates. It is impossible to say whether the same would be true with Trilogy.

Gads.. I should have stayed in Santa Fe.


Clinton A. Medbery, III, M.D.
St. Anthony Hospital Cyberknife Center
(405) 272-7311
buddy@swrads.org or cmedbery@coxinet.net

Clinton A. Medbery, III, M.D.
Southwest Radiation Oncology
1011 N. Dewey Ave.
Oklahoma City, OK 73102

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Calpedaler
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   Posted 8/19/2007 9:15 PM (GMT -8)    Quote This PostAlert An Admin About This Post.
Dr. Medbery,

thank you for taking the time to provide such a comprehensive response, especially while you're enjoying the good life in Santa Fe. Great information and I , and I'm sure others , very much appreciate it.

Mark


CK for a 2 cm AN with Drs. Chang and Gibbs at Stanford, November 2001

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radsrus
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   Posted 8/20/2007 2:11 AM (GMT -8)    Quote This PostAlert An Admin About This Post.
That was an OklahomaCity response. The Santa Fe response would have been "Wow, but don't you see the beauty in all of God's systems?"

One thing I left out was something that is probably obvious but should be mentioned: the amount of solid angle usable by linear accelerator systems is relatively small. THey can only travel in a circle. You can increase the amount of solid angle by using couch rotations, but you are still relatively limited.


Clinton A. Medbery, III, M.D.
St. Anthony Hospital Cyberknife Center
(405) 272-7311
buddy@swrads.org or cmedbery@coxinet.net

Clinton A. Medbery, III, M.D.
Southwest Radiation Oncology
1011 N. Dewey Ave.
Oklahoma City, OK 73102

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radsrus
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   Posted 8/20/2007 2:12 AM (GMT -8)    Quote This PostAlert An Admin About This Post.
And feel free to quote me on the ANA board. But just quote the whole thing if you do.


Clinton A. Medbery, III, M.D.
St. Anthony Hospital Cyberknife Center
(405) 272-7311
buddy@swrads.org or cmedbery@coxinet.net

Clinton A. Medbery, III, M.D.
Southwest Radiation Oncology
1011 N. Dewey Ave.
Oklahoma City, OK 73102

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Steve G
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   Posted 8/20/2007 7:33 PM (GMT -8)    Quote This PostAlert An Admin About This Post.
Thanks Doc, Mark quoted your reply verbatim on ANA, it has provided plenty of grist for our tiny minds to digest, and it will keep us busy for hours. Also thanks for the bonus comment on the "solid angle usable by linear accelerator systems" - something else to chew on, even if it is supposed to be obvious.

Seriously, it is sometimes quite difficult to make heads and tails of all the competing claims. Non-isocentric treatment plus the option for several fractions works for me, though.

Sorry you couldn't stay in that Sante Fe garden forever...

Steve


8mm x 7mm x 6mm AN, left side, diagnosed June 12, 2007, not yet treated.

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