Gamma knife, gamma refers to the gamma rays which are used in this treatment
and stereotactic refers to the three-dimensional manouevering of radiational instruments in space
and stereotactic brain surgery is something that's developed at our hospital by Victor Horsley
in the 1800s and it's after him that the department is named
so, he was the first to devise a frame which is a three-dimensional map of the head
and it has X and Y and Z coordinates so every bit of the brain can be mapped against this frame.
His original one wasn't designed for humans it was a few years afterwards it was adapted but a
gentleman called Lars Leksell at the Karolinska Institute in Sweden used this technology with
his own stereotactic frame for the head and pioneered delivering instead of instruments
into the brain, determined by these coordinates but radiation, and he experimented with different
types of radiation delivery and he was the inventor of the the gamma knife and he found that
sending innocuous doses in multiple different directions and having them cross over to target
points to make a noxious dose was a successful way in creating a noxious radiation injury at the
focal target but the surrounding brain having a dramatically lower exposure to radiation,
so in that way he could reach lesions within the brain; One without opening the head,
and Two without causing significant collateral radiation injury to precious structures.
So, it has been through multiple iterations since
we now have the Icon and Queen Square's built up quite an expertise now in using this newest
platform which gives us a few more options for for treating patients and their comfort, and
each year it's it's an exponential growth in the number of patients undergoing Gamma
Knife radiosurgery as just after the war, Lars Leksell was limited quite extensively by the
sophistication of the imaging now since CT was invented and then MRI was invented we now have
much more sophisticated imaging that we can deliver treatments exactly where we want them.
It can, if necessary. So, it's a day case or outpatient procedure so the patient comes in
in the morning we apply frame which is pinned to the head under local anaesthetic
that's the uncomfortable part of the procedure but most patients tolerate it and by the time they've
they've been waiting for their MRI they're very used to the frame and are much more relaxed. The
actual treatment you don't feel any sensation of the gamma rays so the actual treatment is
painless itself and they can lie in the gantry and ask for their favourite radio station or
just doze off for the treatment, they go home almost immediately afterwards after having a
croissant and a cup of tea, and the frame is taken off. So, in terms of repeating the treatment,
it certainly can be repeated there are small number of patients whose lesions are quite large
and if we deliver a one-off dose to that then the surrounding brain will get a
bit too much radiation than we're comfortable, so we often break it up into what we call fractions
for those patients so three is the commonest number of treatments but these are a small number
of patients the vast majority will have a one-off, one-day visit and treatment. Can it be repeated
again in the future so for example patients with brain secondaries, if they develop other little
secondaries other places in the brain, then certainly these can be repeated.
In trigeminal neuralgia if there's a recurrence then we can also repeat that treatment too.
So, whenever you treat the brain there's important risks to the surrounding tissue
so brain can receive radiation through this treatment and it can cause irritation,
occasionally swelling, and occasionally seizures. That's in the minority of patients.
The target you're treating, so for example if it's a tumour, they can swell it's usually a transient
process, they settle down usually spontaneously, but we do warn patients that there can be
occasionally disability, but the incidence is very low and if you compare that to
surgery then you've dramatically reduced the chance of stroke, wound healing problems,
and if you look at the DVLA guidelines if you have open surgery you are restricted
from driving for much longer than if you've had Gamma Knife for example so it shows that although
the risks of Gamma Knife are not zero they're less in their magnitude than open head surgery.
So, if it depends on the the diagnostic group, so if we take trigeminal neuralgia for example,
a patient who has quite classic trigeminal neuralgia so they have the paroxysmal pain that
is zero and then very severe and then settles down to zero then very severe so they have episodic
shocks, they have the classic triggers; touching the face, chewing, brushing the teeth,
cold wind on the face, they've responded at some stage to carbamazepine these tend to be the
predictive factors of one, this being trigeminal neuralgia, and two them getting benefit from gamma
knife treatments. If they have more of a complex neuropathy then that tends to respond less so
it's very important that you work with a neurologist and that fundamental diagnosis
of trigeminal neuralgia has been made otherwise you have disappointing results.
In terms of other diagnostic groups, I also treated lots of meningioma
and this is a benign brain tumour which benign in 96% approximately,
which causes problems by virtue of it being on the inside of the skull and it can slowly grow and
make its presence felt either by causing swelling to the local brain or by squashing the brain.
So, we tend to treat them when they're reasonably small and certainly when they've started to grow
because that avoids the patient having to go through an open head procedure
and given the choice of gamma knife which is a day case outpatient procedure compared to open
head surgery a lot of them are very keen to to have the incisionless treatment of gamma knife.
So, we warn the patient for about two to three days they might feel
headachy a bit out of sorts but it's unusual for them to have any severe adverse effects.
When the side effects of gamma knife occur, they can be further down the line: three, six,
nine months later, so say it's a gentle treatment but you know it's its effects can be delayed.
So, for example in trigeminal neuralgia we're very careful with patients who already have
facial numbness because it's possible we can make that worse and occasionally in a small number
of patients we can trigger a condition called anaesthesia dolorosa which is a painful numbness
which remarkably some patients say is more unpleasant than the neuralgia itself, thankfully
we've not had that at the Queen Square Amethyst Gamma Knife but we have to vet patients for this.
So, if you look at the successful efficacy, we tend to tell patients this is good for about
three years, there'll be patients who have just a few months of benefit patients and have years
and years and years of benefit, but about three years tends to be the the ballpark,
and of course trigeminal neuralgia during the course of one's lifetime varies anyway
in terms of adverse effects it's a small percentage of causing a severe adverse effect,
so a much lower adverse effect profile than the open surgeries.