AN is located on the cochlear nerve right at the cochlea

[daoisthere]

The Radiologist, that would oversee my treatment with a Gamma Knife Perfextion, has indicated that because of the location of the AN, it would be hard to reach the goal of <4.2 Gy which is recommended in preserving hearing.  He also suggested that the least dosing to the Cochlea would be about 6-7 Gy.

Furthermore, He stated the Cyberknife would have even a harder time achieved any perceived preservation of hearing simply because of the size of it's one beam (Knife) vs the Gamma Knife Perfextion has 200 beams that are more refined.

I have not had a chance to vet a Cyberknife Center. Trying to get through to Barrow Cyberknife. 

Does this sound right?

[PaulW]

What he is saying may or may not be accurate.
It depends on the size, shape and location of the tumour and who is programming the machine
It is true that Gamma Knife can use a minimum beam size of 4mm diameter and Cyberknife is 5mm
But Cyberknife also has the ability to shape the beam to match the tumour shape.

Basically Gamma Knife Zaps you with 201 or 194 little beams and treats a little sphere from 4mm to 30mm in diameter.
As tumours are odd shaped you may need quite a few tiny spheres to treat the tumour. Treating in spheres is not ideal as it can lead to cold spots and hot spots where the spheres overlap or don't. So even treating quite a small tumor say 10x5x5mm you might be zapped with 3 x 5mm shots.. Giving you 3 x 201 Beams
While we might think the beams are razor sharp, they are not... They are in fact pretty fuzzy more like a flash light. This is called the Penumbra, and it is around 3mm for both machines... So that 4mm sphere, is really a 10mm sphere of damage. Its the penumbra that radiates the cochlea. The outside of the sphere will be around 2Gy.


The Cyberknife M6 will treat the whole tumour by shaping the beam and therefor may only use maybe 100 Beams..

Here is a study done by the same institution and same doctors doing GK and CK
The results are the same.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3379795/



 

[daoisthere]

Thanks PaulW...

This gave me great clarity. I am currently seeking a visit with Stanford and Barrow Cyberknife programs.

Daoisthere

[PaulW]

I just re read the original post...
For some reason I thought this was a GK to CK comparison...
The doctor is probably correct it will be hard with either machine to get below 4.2 Gy if your AN completely fills the IAC. Cyberknife does have a little more flexibility in moving beams away from the cochlear, at the expense of putting them somewhere else.
Unfortunately that Penumbra effect which happens with all radiation machines means your cochlear will get something..
I believe that the 4.2Gy figure for improved hearing preservation is the average dose to the whole cochlear. While part of your cochlear might get 6-7Gy the average could be less.. worth asking..
There are slight advantages and disadvantages between GK and CK. but really it comes down to this.. Do you want a clamp on your head or not. The clinical results between the two are the same

[daoisthere]

Thanks PaulW...

[PaulW]

If its any help my AN completely filled my IAC, I had single dose Cyberknife, 7 1/2 years later I still have hearing..
I have lost high frequencies but low frequencies remain normal.

[daoisthere]

PaulW..

This is super helpful. One of my candidates is Penrose Cyberknife in Colorado Springs. They would treat with a 12Gy single dose.

[Freelander]

This is a follow-up to PaulW regarding his CK treatment.   It seems that you had a small tumor and ultimately chose CK.  As of 6 months ago, my tumor was about the same size as yours and I'm curious what led to your decision to have treatment when it was that size and why you settled on CK, as well as where you had it done.   My most recent conversation with a doc was to continue to watch and wait; and my tumor is located back in the canal right at or close to the cochlea.   As I am a newbie, you may have already posted this elsewhere on this site; if so, just tell me where.    Thanks.

[ivana]

PaulW..

This is super helpful. One of my candidates is Penrose Cyberknife in Colorado Springs. They would treat with a 12Gy single dose.

Hi, please let me know how are you today after 3 years and CK treatmen? How is your hearing? Thank you!