Linda,
I think any of the machines currently on the market can be reasonably effective on treating AN's. That being said, it is also a natural tendency for everyone to feel they either used the "best" machine or had surgery with the "best" doctor. In the world of radiation treatments there are only two machines that are designed for a radiosurgical application which are CK and GK. This means they are capable of high accuracy, high dose treatments in single (GK) or multiple fractions (CK). The positioning is done either with an invasive headframe (GK) or without through active targeting (CK). GK is limited to intercranial tumors while CK is capable of delivering radiosurgical precision to tumors elsewhere in the body. Triology and Novalis are radiotherapy machines which are very effective in a variety of applications throughout the body and can approach, but not equal the accuracy of radiosurgical machines.
Accuracy of these machines needs to be understood and measured in the same ways. There is machine error, frame error, Scan error, etc that roll up into "total error" which is the only meaningful number in my mind. CK has been shown in peer reviewed clinical studies to have a total error of around .89 mm. GK is shown in studies in the range of 1.2-1.5 MM and Novalis and Trilogy are in the 2 mm range. When statistics are quoted less than that they are generally only showing one component, usually machine error.
The other issue crystallady's neurosurgeon raised was the ability to dose the tumor in a uniform manner, but the claim that Novalis does it better just because of the shape of the collinator is just plain wrong. it errantly dismisses the accuracy factor and in the case of CK does not address the technology that allows the beams to be shot from more angles than the other three machines which are fixed beam.
In terms of her neurosurgeon's preference of Novalis to GK or CK, that would be meaningful to me if he/she had access to all three and still opted for the Novalis. My guess is that is not the case, and unfortunately most docs in today's world won't tell a patient "I really prefer brand X, and we only have brand Y here so I think you should go down the street to be treated. I'm not picking on Novalis as the statement applies to any doc making such a statement about any of the machines.
I think you can have an effective treatment with any of the machines in the hands of an experienced team, but it does bother me when folks post "absolute" statements about a machine without providing something other than their particular Docs opinion. However, since that tends to be the norm
, I posted Crystallady's post over on the CK board and here are Dr. Medbery's comments, take them for what they're worth
Good Luck in your decision making
Mark
First, single treatment very likely increases the risk of hearing loss. That is exactly why we always treat AN patients who still ahve hearing on the CK, although we also have GK available.
Second, I would bet the neurosurgeon either does not have access to CK or GK at this time, or has an econnomic interest in the Novalis. I have never met a neurosurgeon who would prefer Novalis to either CK or GK.
Third, although the CK used round collimators, it does not simply overlap round spots. It uses non-isocentric treatment that "paints" the dose throughout the tumor. I am quite confident that Novalis cannot get better homogeneity. Either the neurosurgeon does not really understand the technology or was being disingenuous.
FOurth, it is not certain whether hot spots in the tumor are bad or good. An extended discussion of this concept is beyond the purview of this board, but please accept that there is debate that is unresolved.
Clinton A. Medbery, III, M.D.
St. Anthony Hospital Cyberknife Center
(405) 272-7311
buddy@swrads.org
