10 week post SRS, can anyone answer this question?

[Alison]

Hi everyone, Alison here. I haven't posted for a while as I've had other health issues and am also sorting moving my Mum, who has dementia, to a care home, which is taking up all my energy reserves :0) But I had my follow up apt Monday ,10 weeks after my linac radiosurgery and wanted to report back. I have had increased dizziness and balance issues in the past few weeks, worse than before treatment. I guess it's a  reaction to SRS or swelling. ( MRI not until Jan 14). But I was confused by the oncology doc who said that the cochlea and facial nerve would have been radiated as this always was the case. I was under the impression they tried to avoid these structures, or is it just less of a dose received by them than the tumour? Also when I asked how far was the tumour from the brainstem she said 2mm. I said 2mm was close if swelling occured and she said 2mm was good as it gets? My An is 14.5 x10 in IAC and CPA. My dose was 12g over 80. If anyone can shed some light on this I'd be very grateful x Hope you are all well.

[ppearl214]

Hi Alison,

Congrats on being a "Postie Toastie"

There are meds, post treatment, that can help the issues that you have noted. Many times, a steroid med (such as Decadron for edema, low dose, short-term valium for dizziness, etc) can be of help to calm things down.  Many here report that these meds have helped post radio and you may want to consider their use to help.

I'm a little confused by what your radio-doc has noted as you are correct... they try to avoid contact with the cochlea and facial nerve but not always the case.  We know head MRI's have a total margin of error of +/-2mm.  Your next MRI should give indicators if edema or such is going on.  But, in the meantime, keep your treating team (the neuro-onc) on your team aware of what is going on as they will want to track any post-radio issues and prescripe as needed.

I hope this helps.
Phyl

[Alison]

Thanks Phyl for the reply.

I wouldn't want to take steroids unless essential, but thanks for the advice about which ones help. 

I'm also a bit confused by the doc, I don't know why she couldn't be more specific. I had to ask questions rather than her volunteering information about the dosage etc, she was rather vague and she was the doc that planned my treatment. She never would answer questions about tumour volume, for example. My son, who came with me, agreed she was vague. I didn't think to ask what dose in gy the surrounding tissue received. But I am in the UK and didn't have a choice of treatment centre, maybe linac is less precise!

Alison

 

[mk]

Hi Alison,

There is no way to avoid the various nerves using SRS. Since they are essentially in the way, they do receive a dose of radiation unavoidably, and this is why radiation may result in hearing loss and (more rarely) in some facial nerve problems. This is why fractionation is considered by many more beneficial, since it allows the healty cells to heal, before receiving the next dose.
Simplistically speaking, depending on the SRS method the maximum dose is delivered at the centre (for example in GK), but the amount declines sharply at the edges of the tumor, so that the surrounding structures are not affected. CK is considered to deliver a more uniform dose.

I am a bit surprised by the statement that your AN is only 2 mm from the brainstem, this seems too close for a tumor of your size. Perhaps the doctor meant the cerebellum? Some doctors are very vague and not forthcoming, and this is frustrating, but this is their style.

Regarding the symptoms, what you describe is not unheard, especially so early after radiation. Typically symptoms tend to crop up within the first 6-12 months. I am a bit surprised by the fact that your next MRI would be in one year, I think that standard here in N. America is 6 months after radiation treatment, depending of course on the doctor's judgement.

Marianna

[nftwoed]

Hi Alison;
   In IMRT, the cochlea and facial nerve are not avoided. Nor are they avoided with GK. Otherwise, there may occur 'cool spots' in the tumor boundry. Colateral damage has been hypothesized to be less by the use of fractions of a total dose, unlike GK. Fractions also theoretically allow for a higher total dose.
   Re, steroid use, yes, if it can be avoided. Many have quite a few side effects from those.
   I'm unsure what the nurse meant.
   Do you know the linear measurements of your AN?
   Best wishes in all.

[arizonajack]

I was confused by the oncology doc who said that the cochlea and facial nerve would have been radiated as this always was the case. I was under the impression they tried to avoid these structures, or is it just less of a dose received by them than the tumour? My dose was 12g over 80. If anyone can shed some light on this I'd be very grateful x Hope you are all well.

I'm about 10 weeks post Gamma Knife. Maybe I can explain it.

The radiation beams cannot avoid the structures surrounding the tumor. The beams go through those structures at a much lower dose which should be harmless to those tissues.

Draw an oval on a piece of paper. Make the oval 15mm x 10mm. For the purpose of this explanation that oval is the shape of the tumor. That outline is also called the 50% isodose line. That means that the radiation dose as it goes through the outline is 50% of the dose that converges on a point inside the tumor. If you got 12g at the 50% isodose line it means the center of your tumor got 24g. Now draw another oval a little outside outside the first oval away from the first oval. That second oval is the 25% isodose line which means that any structures at the 25% isodose line only got 6g and further out got even less.

I don't know where the 80 comes from. It would mess up my example if the first oval was an 80% isodose line.

The alternative is that the radiation covered 80% of the volume of the tumor but that doesn't make sense. My GK covered 99% of the volume of the tomor.

Do you have a copy of your radiation report and quote it, we might be able to make more sense out of it.

[PaulW]

Essentially the tumour was treated to 12Gy to the 80% isodose line which means the maximum dose to the tumour was 12 /  80% = 15Gy
One of the potential critisisms of gamma knife is its typically high maximum dose, which could affect the nerve within the tumour..
Mind you, dose fall off on Gammaknife is a lot steeper, which is something in favour of Gamma Knife

[Alison]

Hi, thanks so much to all of you who have replied and given me a better idea of what went on in my treatment. The dizziness and imbalance are making me very wobbly at the moment. I was told this could come and go for up to year but I think many of us have had these symptoms for longer post SRS. I was told no MRI before a year as "it'd only show swelling if anything".I asked about vestibular therapy/exercises and the doc hadn't heard of them.

Yes it was 12Gy with 80% isodose. The machine was linac as that was my only option where I live in the UK. That was all the information I was given. I get much better explanations and information on here than from any of the docs I've talked to!

I've never been given volume size, only the approximate measurements of 14.5mm ( to 15 mm) by 10mm by 8 mm, IAC and into CPA. We don't get copies of our radiation report or any information about it here in Blighty. Nor do I have the MRI films.  I had to ask to even get the 12 Gy 80% information but this wasn't accompanied by any explanation as to effect on surrounding tissue! 

Thank heavens for ANAUSA!

Alison 

[Alison]

Hi,

I've now received some more specific info about my dose of SRS. A letter came in the post today from the oncology doc, copying me in to a letter sent to my GP and the neurosurgeon. It's almost as though the doc had read my mind and given me some more specific info!

"The dose was 12Gray to the 80% isodose, dose to left trigeminal nerve was a max point dose of 6 Gray with an average of 3 Gray, left cochlea was max of 9 Gray with average of 5.7 Gray"

Don't know if any of you can explain that please.

In reality the results are I cannot move my head more than a few degrees off centre without vertigo. This has got worse each day. Hoping it may settle.


Thanks Alison