How Cyberknife and Gamma Knife differ in treating the volume of the AN

[daoisthere]

Keep in mind that the AN is not 2D. It is a volume. A cubic AN.

Case 1: Although the gamma knife claims great accuracy, It sort of is like pointillist art.  You've got 200 beams of a diameter of about .3mm pointed at the AN with 100% dosing of a total of 12 to 13 grays. That's 60mm set in stone.  The beams are static and have no regard for the collateral of the surrounding area.   Something is going to get toasted.   You are pretty much depending on your pointillist radiation settings provided by your choice of expert provider.

Case 2: Although the cyberknife is less accurate.  It's more like paint brush of 1mm which allows you to target the 1mm spaces inside your 3D AN.   More like a modernistic painting.  The single beam is not static and can follow the trace of the AN volume.  Allowing for less collateral.

Perhaps this is why places like Stanford are more successful with preserving hearing.

This is just a guess.   I wish more providers would comment in this forum honestly.  I just can't get over the idea of why the studies in general suggest that cyberknife presents less collateral.

Peace,
Daoisthere

 

[ANSydney]

I would say that Gamma Knife is spatially distributed, while Cyberknife is temporally distributed. In the end, pretty much the same effect. The 12 to 13 Gy does not refer to the tumor dose, but the dose at the 50% isodose. The centre of the tumor gets a higher does and it falls off outside the tumor. Both would have collateral damage as the single beam (in space or time) traces through healthy tissue.

Proton beams sound interesting because it's possible to actually increase the dose and then suddenly drop as it travels in tissue, while photons (as used in Gamma Knife, Cyberknife, LINAC etc) drop in dose as they travel ( https://en.wikipedia.org/wiki/Bragg_peak ).

If you really want to see the way of the future (unfortunately not now), look into MRI guided focused ultrasound. Lars Leksell looked into ultrasonic surgery before settling on the Cobalt-60 ionizing radiation treatment used on the Gamma Knife. MRI guided focused ultrasound can be used for surgery or temporarily opening up the blood-brain barrier to let pharmacological access to the tumor.

Do you have a study that shows Stanford's outcomes for hearing preservation. (From what I can gather hearing deterioration happens over years and by 10 years, very few are spared).

[ANSydney]

For MRI guided focused ultrasound, we were 6th on the priority list in 2009 https://www.fusfoundation.org/news/360-fus-foundation-sponsors-landmark-mrgfus-brain-workshop . One day.

[PaulW]

Ok here are some comparisons between CK GK and Proton therapy.
Unfortunately physics gets in the way determining how accurate these machines are.

First of all...
Proton therapy.
Do your own research.
There is this lovely thing called range uncertainty.
Just like Heisenbergs uncertainty principle, there is uncertainty as to when a proton will release its energy. So accuracy in Proton Therapy is +/- 3mm and it is unlikely to get much better because of physics. It also treats to the 120% isodose line.. which means if the middle of the tumour gets 12Gy the edge of the tumour and often the surrounding tissue like the cochlear and trigeminal nerve gets 14.4Gy. Little wonder the hearing and facial nerve preservation statistics for proton therapy are far lower than photons ..(GK or CK). Proton Therapy has its place, but it is not well suited to small tumours, that touch critical structures.

GK.
They may well flaunt 0.3mm accuracy.
But the minimum beam size is 4mm, and they don't like using that because of the penumbra effect. At 4mm you mainly get penumbra and not much beam. So typically 5mm is the smallest beam they will use.
There are other problems with the accuracy claim.. the MRI scan is done on 0.5mm slices which often means the imaging can only be relied upon to +/- 0.5mm at best. The head frame is also not 100% rigid and there is some flex.. Given the surrounding 2-3mm will get hit by the penumbra effect of the beam, the accuracy of the imaging etc, arguing over 0.3mm accuracy between CK and GK becomes an academic argument and has little or no bearing on real world results.

CK does typically treat to the 80% isodose line versus GK to the 50%.
What does this mean?
The middle of the tumour gets toasted with GK and receives 24-26GY
While CK the middle of the tumour gets 15-16.25GY
No big deal if the middle of the tumour is tumour... but for AN's it could be the nerve.
No clinical advantage or disadvantage has been found to date.

CK verifies the tumour location at the time of treatment while GK does not.
This means if there is a mistake in setting up a patient for GK there is a higher likelyhood of treatment failure.

Either machine is a great option


The results from the two machines

[ANSydney]

Paul, that's an excellent description of the mechanics of the various radiotherapy options. It's good to have such expertise on the forum.

For proton therapy, I thought getting an increased radiation intensity as it traveled, then stopping, was a good thing, but as you pointed out, this means that the tumor border is at a highest intensity (at least on the entry side). I liked the way the "bullet" can be stopped before it exited and therefore spared the healthy tissue the other side of the tumor.

Does the uncertainty as to when the proton releases its energy affect angular accuracy or distance along the path accuracy?

Good point about the middle of the tumor getting toasted with GK, since in the tumor may be the nerve it's growing on.

When is the medical profession going to come up with a treatment for vestibular schwamnomas? Something that improves you rather that creates more havoc.

In your case Paul, it appears that you have had a good outcome. After 7 years how is your hearing going?

[daoisthere]

Here is the study siting the founder of CK at Stanford:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3842077/

Thanks for all of the clarifications.  Key contributes of the study:

< 4.2Gy to the cochlea to preserve hearing
> 5.3Gy to the cochlea equals hearing loss

Peace,
Daoisthere

[daoisthere]

Ultrasound therapy 'sounds' intriguing.  I am off making a decision because of a situation with a co-morbidity.  Thanks for the feedback.  It is helpful.     

[rupert]

Just to be clear so as not to confuse newbies. It's not just a beam pointed at the tumor and that's it.  In my treatment, they used three different sized columators.  A medium (don't know the size of holes) first,  that was treating the portion inside the inner canal.  They then switched to a larger hole columator for the bulk, biggest part of the tumor and then switched to the smallest size columator for treating the perimeter of the tumor.  That took the longest.  The table also moves and tilts all during the treatment.

[daoisthere]

Hi Rupert,

Would you please clarity which therapy you are speaking of?

PaulW and ANSydney,

Awesome contributions... I have been suspicious of the .3mm specification of the GK.  Part ownership of the therapy skews one's recommendation.  Nice cars and homes have to be paid for!

Peace, (I will remain on watch and wait for at least another year)
Daoisthere

[rupert]

Hi Daoisthere,  I had Gamma Knife.  UPMC in Pittsburgh with Dr. Kondziolka.

[ANSydney]

daoisthere, congratulations on deciding on observation. After another year, you'll have three MRIs that will not only show you any growth, but also the rate of change with time.

Have you had a chance to look at your MRI images and take measurements? (It's easy to do if you get the CD)

Remember, most tumors do not grow and only a very small amount grow enough to create problems.

I like your statement:

Part ownership of the therapy skews one's recommendation.  Nice cars and homes have to be paid for!

Unfortunately there is a conflict of interest. In an ideal world, an expert would determine the best treatment, including observation, for you and then you would find a treatment provider. In the mean time it's left up to us to become the ones to become experts on which treatment is best. In Denmark (and many other countries), where there is no distortion, 95% of tumors under 2 cm go to observation. Contrast that to the US!

[PaulW]

Hi ANSydney,
Protons travel through you, slowing, until they reach a certain speed/energy, when all of their energy is released at once.
The problem is you never know exactly when a proton is going to release its energy.
Unfortunately this uncertainty is around +/- 3mm
So the inaccuracy is predicting the depth of the beam.

[Freelander]

Hi All,

I am a newbie to the forum too, though have been diagnosed almost three years ago.   About proton therapy, most of the negativity that I have read comes from the exorbitant cost of the facilities to create and maintain them, as well as the skilled training needed.   PaulW's comments about a 3mm range of uncertainty are alarming, for that is a big number for potential error within the fragile areas wherein an AN can grow.   I would like to read current research which identifies inaccuracy as a common flaw in proton therapy, and what the work around is if proton therapy is used.   If you have a link or other substantive information available, I would love to read it.

Thanks to everyone who participates in these conversations for sharing their concern, knowledge and experience.   

[PaulW]

http://medicalphysicsweb.org/cws/article/research/50584
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374500/
http://amos3.aapm.org/abstracts/pdf/77-22619-310436-91773.pdf
Proton Therapy does have a place....
Treating small Acoustic Neuromas, probably isn't its strength.

[ANSydney]

Thanks Paul for the information. Good to get facts rather than speculation. I've printed out the second referenced article and will read it on the bus this evening.

One thing that is surprising is the cost of a proton therapy facility. Something like US $80  million versus US $5 million for a Gamma Knife facility. And the ongoing yearly costs are about 10% of the initial capital outlay. There has to be a damn good advantage to proton therapy to justify that huge cost difference.

One picture from the third reference caught my eye. It's on the third page. It shows how photons have a gradually dropping intensity as they travel, but protons increase in intensity and then drop of to nothing. So the "entry wound" would be less and the "exit wound" would be non-existent. So, less health tissue is damaged, at least a few millimeters before and after the tumor. If only something could be done about the range uncertainty, protons may be worthwhile.

It would be nice to have an unbiased study (do they exist) that compares protons to photons.