GAMMA KNIFE

If one suffers from cancer, the chance of having BM is up to 20%. BM can be single or multiple, small or large, silent or causing a lot of neurological problems. In the past, surgery and whole brain irradiation were the standard treatment in most cases. However, not every metastasis is amendable to surgery. Not every patient is fit for surgery. Not every brain metastases patient prefers whole brain irradiation if there are other options.

The Gamma Knife Icon revolutionises the treatment of BM in selected patients: It is non-invasive.

It takes half a day to complete.

Concurrent medical treatment such as chemotherapy and target therapy can be continued without interruption.

For large lesions, one can choose open surgery followed by tumour bed Gamma Knife radiosurgery; or for the medically unfit, adaptive Gamma Knife in 3 sessions over 6 weeks is also effective.

Multiple BM, up to 10 or even more, can be treated in one single half-day session.

Unlike whole brain irradiation, it can be repeated as required for new or recurrent BM detected during follow up. It is not rare for some long survivors to have more than several Gamma Knife treatments.

There is no hair loss or treatment related neuro-cognitive damage which impair quality of life. With modern treatment of cancer, patients with systemic disease and BM live a much longer life than before. Quality of life for them is a top priority. By preserving quality of life in these patients, the ICON may become the standard of care in the future.

AN or VS is a benign, usually slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear. Koo’s classification is useful to guide treatment:

• Purely inside internal ear canal
• Grows outside but not touching brain stem
• Touching brain stem
  • Indenting brain stem but not displacing 4th ventricle.
  • 4th ventricle displaced.

In the elderly, and when the tumour is incidental and small, monitored observation suffices. Otherwise, Gamma Knife offers excellent (>95%) long term control for Koo’s stage 1 to 4A tumours. Facial palsy is near zero with today’s technology. Hearing preservation is around 50% but variable according to the individual case.

For large tumours (Koo’s stage 4B), the best treatment is planned surgical excision to decompress the brain stem, followed by Gamma Knife of the remnant later. Facial nerve preservation is better than 90%, and late recurrence is very rare.

AN is well known to develop transient tumour necrosis and swelling months after Gamma Knife. This phase normally lasts for 6 months, then the tumour started to shrink. It is very important not to associate transient swelling with treatment failure.

Most cortical meningiomas on the surface of the brain are best treated by open surgery, if they are large and causing neurological symptoms. The role of Gamma Knife for cortical meningiomas will be confined to small remnants of tumour attached to important veins, venous sinus, etc, left after surgical removal of the main tumour mass.

However, for skull base meningiomas, Gamma Knife is an important tool for the neurosurgeons. Smaller lesions without pressure on the brain stem or optic pathways are best treated by Gamma Knife alone. Large skull base meningiomas are best treated by combined microsurgery and Gamma Knife. Surgery is not aimed for radical excision, which is likely to produce new neurological damage, CSF leak, and prolonged recovery. Rather, the neurosurgeon will remove the part of meningioma which compresses the brain stem, temporal lobe, or optic pathways. The remnant which is attached to bone, cavernous sinus, carotid artery, etc can be adequately dealt with by the Gamma Knife.

Some meningiomas are more aggressive, and may behave like a malignant tumour. Traditionally, such tumours were treated by fractionated radiotherapy. The Gamma Knife ICON in a mask mode, with its accuracy and sharp radiation fall off, is now an option. The same applies for optic nerve sheath meningiomas, para-optic meningiomas, or the latter’s recurrence after previous RT.

Pituitary Tumours and Craniopharyngiomas

Most symptomatic pituitary tumours, whether endocrine a ctive or non-functioning, are best treated by microsurgery, usually via the trans-sphenoidal route. The Gamma Knife is very useful when the tumour invades the cavernous sinus, which renders total excision difficult and risky. The concept of combining the merits of microsurgery and Gamma Knife applies here: do no harm (conservative resection), remove harm (decompress optic nerves and chiasm), and prevent future harm (Gamma Knife for remnant to prevent future recurrence).

For acromegaly and Cushing’’s disease of pituitary origin, surgery is the primary treatment. Gamma Knife is useful s adjuvant therapy when surgery alone cannot effect cure.

For prolactinomas, medical treatment is the first line treatment. When medical treatment fails, or not tolerated because of side effects, Gamma Knife is then a good option.

Craniopharyngiomas is a very difficult tumour to eradicate surgically, because of its central location and adherence to the hypothalamus. Gross total resection is not always possible without creating devastating consequences. It also tends to recur despite repeated treatment. Combined microsurgery and fractionated Gamma Knife ICON treatment provide the way forward for resilient cases.

These tumours comprise a great variety from gliomas to primitive neuroectodermal tumors. In the past, Gamma Knife is reserved for local boost after radiotherapy, small residual disease, or as salvage when conventional therapy fails. With the capability of the Gamma Knife ICON for fractionation, a new radiation delivery platform with greater accuracy and much reduced radiation spillage enters the armamentarium of the neuro-oncologist.