Difference in types of radiation?

[allegro17]

I was wondering - could anyone tell me what the difference between FSR and CK is?  I know some ways they differ from GK but am not sure how they are different from each other.  I am asking as I just spoke with Dr. Lederman about FSR, which he does in 5 doses of 400 rads, over 10 days.  I thought that CK did essentially the same thing?  I have tried to contact Dr. Chang at Stanford but no response yet.

Thanks so much!

Laura

[sher]

Laura,
I had CK... but not sure what the difference is. You can go to the cyberknife support site and there are a couple of docs there that will answer your questions.

http://www.cyberknife.com/Forum.aspx?g=topics&f=2572

I hope this helps.
Sher

[sgerrard]

Oh, I'll step up with a 2 minute overview of radiation systems.

Traditional FSR was 25 to 30 days of treatment, with about a 1-2 Gy dose per day. (1 Gy = 100 rad, except all the fine print...). It is delivered using a linear accelerator on a robotic arm.

Gammaknife is a single treatment, for the last decade or so about 12-13 Gy. Historically it was higher, around 25 Gy. Your head is clamped in a metal halo for the treatment, and the radiation source is cobalt, not a linear accelerator like the others.

Cyberknife is also a robotic arm, which is connected up with real time x-ray machines, so that it can position with higher accuracy. The treatment is typically 3-5 days, with 5-6 Gy per day. Your head is held to the table with a plastic mesh mask.

The latest trend in FSR is hypo-fractionation, meaning fewer fractions, and more use of head restraint. Linac, Trilogy, Novalis, and other brands are now doing this shorter version of FSR (maybe it should be called HFSR), with 5 days of treatment, and doses in the 4-6 Gy range.

I think it is fair to say that hypo-FSR is very similar to CK, except that I believe Cyberknife has a patent on the real-time x-ray connection, so that the others can't duplicate that feature.

Okay, overview done. 

Steve

[windy]

Hi,

I read my notes regarding my GK treatment.  My notes stated I did have a maximum of 25 GY the day of my treatment with lowest doses at 12.5 GY.  Is 25 GY normal these days?  Also they radiated my trigeminal nerve and brain stem with 10 GY and 13 GY, respectively.  Also, my notes stated the tumor was pressing into my brain stem, prior to GK.  I was not expecting the brain stem issue or the amounts of radiation used and where they were used.  I thought that only the tumor was targeted.  I did not know the brain stem and trigeminal nerve are also targeted.  Has anyone found a similar report in their records?  Just curious........ 

[sgerrard]

Hi Windy,

Is that from the actual treatment report? I haven't seen mine, but I suspect that they are recording something like "maximum possible exposure," or the dosage level near the various nerves. I don't think they actually target the brain stem, but they might well note something about how much was possible based on the treatment plan.

I had a consultation with a GK facility, and they said that if they did GK, they would use 12-13 Gy. That is probably the number for the tumor itself, which is what is usually quoted when talking about treatment dose. It is my impression that GK is usually done at that level now. You may be reading something more technical that is recorded on the treatment report as a matter of record.

Steve

[tony]

First class on the different applications/formats - I might add :
Gamma is not one beam but 250 plus smaller beams
that under computer control  are concentrated on the one point
I would add that the gamma format differs in as much that it acts
like a magnifying glass - puts most, if not all, the concentration
on the target area - to within less than 1mm
This (to a degree) explains why the gamma can be done
in a single shot format - there is less chance of entry
or exit damage to other tissue (quite important in a human brain ?)
basically the local tissue gets only 5% of the concentration effect
and "collateral damage" is much reduced
FSR is an older method (20yrs +)
gamma now (15ys+)
while CK is a bit more recent ?
Yours
Dr Spock

[Larry]

The difference in GY level is interesting - around half these days you say Steve.

mmm, wonder if they found 25 Gy too much with too much colatteral damage. Be interesting to see what my man says later today when i see him.


Laz

[sgerrard]

Something like that.

They used to use only a few focus points, before the days of readily available MRIs (~1992). Since then, they have used MRIs to plot more focus points for finer control, and at the same time have been able to reduce the overall dose. The result has been improvements over time in reducing facial nerve issues and retaining hearing. Read all about it:

http://www.acousticneuroma.neurosurgery.pitt.edu/gammaknife.html

Steve

[mk]

Windy, the difference in the doses that you are reading refer to the average dose, versus the maximum "marginal" dose. In GK, the radiation is not delivered homogeneously, rather the tumor is divided in "isocenters", and the radiation distributed (or something like that). So the "maximum" dose was 25 Gy (typical values are around 25-26 Gy, or even higher), whereas the average was 12.5 Gy (again a very common value).

Based on what I read in the medical literature, the GK doses back in the 90s were more like 17-18 Gy. These doses resulted in high levels of nerve morbidity.

Marianna

[sgerrard]

I'll go with what Marianna said, she sounds like she knows what she's talking about. 

Steve

PS: The link for Pittsburgh said the earlier level was 18-20 Gy (meaning the average dose). I stand corrected on that too. 

[windy]

Thanks Marianna and Steve!  I feel a little better now about my max. dose of 25GY.  I went back and read my notes to refresh my memory and they stated "a maximum mean dose of at 25GY at the center of the tumor".   I suppose now that is standard.  The maximum mean dose for the brain stem was 13.4 GY and the fifth nerve was 10.7 GY and 4.7GY.  I suppose I would have never even gave it a second thought had I breezed through my recovery stage.  But, based on my strong reaction afterward I was beginning to think I was some sort of experimental case!  Ha!  I have been told by another radiation oncologist that I was given maximum GK doses when he was told of what they used and where, in my particular case.  It is good to know my doses are more typical than I realized.  Thanks everyone!

[Larry]

I just spoke to my Oncologist (does these things too) and he recommended to me a fractionated approach with a total of 22Gy's over 5 episodes. His reasoning for the fractionated v's the single shot was because my AN is pressing on the brain stem.

Sounded logical to me. Actually, I'm happy to not have the helmet screwed into my skull either.

Laz

[allegro17]

Actually, this brings me to another question.  I am now pretty sure I want to go the route of radiation and not surgery.  I spoke w/ Dr. Chang at Stanford on the phone on Friday and he was SO nice and helpful.  He talked to me about CK extensively - it seemed that the main difference would be that in the case of preserving the hearing nerve, CK is slightly better because fractionating the radiation is much gentler on the hearing nerve, but that there is less of a difference in how "gentle" CK and GK are on the facial nerve.  Does this sound right?
I am wondering how much of a difference this should make in considering my options as I do not have any usable hearing left on the AN side.  I haven't really spoken with any GK experts but have appts. in a few weeks.
Is there anything else that makes one "better" than the other?  I am not too put off by the GK mask.  Just wondering how one lists the "pros" and "cons" of each here when the hearing nerve or mask isn't so much of a factor.  Does one procedure tend to have more/different side effects?  What side effects have you experienced, if any, and were they severe enough to interfere w/ your everyday life?

Thanks,

Laura

[Larry]

Laura,

I really think its 6 of one and half a dozen of the other. I was told that i won't know if the facial nerve has been damaged for a month or two after the procedure so I'm not going to worry about it.

The key issues that i have read from the many posts on this forum are the screwed in helmet v's a mask and the one off hit v's 4 or 5'ish.

Eirther is fine - ask Dr Chang what he would do given the size and positioning.

laz

[sgerrard]

Hi Laura,

GK and CK are pretty close in the main things, meaning control of growth and avoiding facial nerve issues. Some will quibble about "mechanical accuracy" versus "overall accuracy", or even "iso-centers" and other arcane stuff (usually in favor of whichever machine the doctor uses), but I have never seen any report on outcomes that shows a meaningful difference beyond an edge in hearing preservation for CK, and maybe a gentler pattern of swelling after treatment. I picked CK, put I would have no problem doing GK instead.

Steve