Gamma radiation therapy is a form of delivering highly focused radiation
to lesions in the brain that are generally inaccessible to open neurosurgery.
Gamma knife is used to treat a variety of both benign and malignant conditions in the brain
ranging from metastatic brain tumours. That is to say tumours which are spread from
cancers elsewhere in the body through to common benign intracranial tumors, such as meningiomas.
And Schwannomas. Through to pain conditions, such as trigeminal neuralgia and also vascular problems
such as brain arteriovenous malformations or AVMs. Conditions which usually have been
present in the patient for many, many years, but have an ongoing risk of brain haemorrhage.
So, the gamma knife is used for quite a wide variety of conditions in the brain.
Well, that depends on what pathology one is treating, but generally speaking, gamma knife is
most useful and works best and is least risk the smaller the target, because radiation side effects
increase the larger the target. But then when one talks about the different pathologies, it
then becomes different and it's more to do with what the patient is like.
For example, in patients with brain metastatic tumors, it really depends on the number,
the disease burden in the brain and how the patients
is faring in terms of their cancer elsewhere in the body, for example.
On the one hand there are technical aspects to what makes a good candidate.
On the other hand, there are quite important clinical
aspects, depending on what the actual pathology and the clinical problem is.
So, you know, just like open neurosurgery patient selection is the key. If you get
your patients selection right, and treat the right patients, then the outcomes are very good.
That is to say with metastatic tumours, we know we can control the growth of
those tumours in over 95% of cases. And in trigeminal neuralgia, if a patient has
true neuralgia and is otherwise a good candidate, then we get very good pain relief from that.
The issues come when one stretches the indications for patients who are perhaps,
you know aren't going to be quite as good candidates as the prime candidates would be.
The main risks of gamma knife are, again, unlike open brain surgery, there are delays and nothing
happens immediately, post-treatment, so all side effects and risks tend to occur several weeks,
if not a few months later. That's to do with the effect of the radiation on the lesion in question.
For example, in trigeminal neuralgia, some patients get facial numbness
appearing several months later, and that's due to the radiation effect on the nerve.
Conversely, when one treats tumours, they can swell up
after a few months. And that can cause either pain or headache or even seizures.
So that's one aspect.
The other aspect is to do with this small amount of radiation that affects
the surrounding brain tissue. And again, that can cause a brain reaction, which can
cause side effects such as headache or weakness or even seizures.
Gamma knife is performed nearly always under local anaesthesia as a day case. So, in terms of
recovering from the actual treatment, that may be just a day or so, really of a bit of headache and
feeling out of sorts. So, that's a good thing, but unlike open surgery, any issues can occur
later on which may then require recovering from. Most patients have Gamma knife once.
So it's a one-off treatment. It's not what we call fractionated treatment. Generally, it's a one-off
treatment, but if it's successful, for example, in metastatic brain tumours and the patient
suffers some more, then they can also be treated. So it's not necessarily a one-off, but usually is.