Gamma Knife procedure an innovative option for treating cerebral metastases

Key Points

Sydney - Effectively treating metastatic melanoma remains a challenging task, and this is particularly true when the tumor spreads to the brain.

"Gamma Knife radiosurgery is a superior method of treating either single or multiple brain metastases," says Michael A. Izard, M.D., FRANZCR (Fellow of the Royal Australian and New Zealand College of Radiologists), Radiation Oncology Associates, Macquarie University Hospital, Sydney. "The novel procedure is not only a patient-friendlier option to traditional surgery, but as effective as whole-brain radiotherapy in the right patient."

According to Dr. Izard, WBRT can treat metastatic melanoma lesions, but the radiation will also impact healthy brain tissue, causing significant neurotoxicity as well as alopecia, nausea, vomiting, lethargy, otitis media and sometimes severe cerebral edema. The Gamma Knife procedure is much less toxic and less traumatic, delivering with pinpoint accuracy approximately 200 low-intensity radiation beams to one or more targets in a single session.

"Gamma Knife radiosurgery can be a very useful tool when you have several metastatic lesions or when the patient has failed whole-brain radiotherapy. Moreover, the treatment can help maintain and improve the patient's quality of life, particularly in the patient with controllable extracranial disease," Dr. Izard says.

How it works

Approaching the tumor from multiple directions and focusing on metastatic lesions individually, the Gamma Knife treats each lesion with a smaller dose of radiation traveling through each of the beams, thereby causing less damage to surrounding cerebral tissue. The latest model Gamma Knife (Perfexion, Elekta) has 192 non-coplanar radioactive cobalt-60 sources arranged in five rings around a fixed focal point. These sources are aligned to focus directly down onto one 4 mm sphere at the target center with an accuracy of less than 0.15 mm. After identifying the cerebral lesion to be treated, the clinician can aim and fire a high dose of radiation at the target lesion while sparing critical surrounding tissues, Dr. Izard says.

Compared to WBRT, both traditional surgery and stereotactic treatment with a Gamma Knife are both superior treatments for a solitary lesion, Dr. Izard says. The Gamma Knife trumps traditional surgery, however, in that it is a more cost-effective and much less invasive approach.

In relation to survival, those patients with a single metastasis and no extracranial disease will likely have the best prognosis, followed by those with controlled extracranial disease. The ideal patient for a Gamma Knife procedure would be someone who has one or several cerebral metastases and absence of - or controllable - extracranial melanoma disease.

"A Gamma Knife procedure would be ideal in those patients with up to five cerebral metastases. In a patient with six or more metastases, I would opt to use WBRT and then follow up with a Gamma Knife treatment, should any lesions persist and progress," Dr. Izard says.

According to Dr. Izard, choice of treatment is often made according to the extent of both intracranial and extracranial disease, which directly impacts the quality of life of the patient. The Gamma Knife will not have any impact on extracranial disease, but it should have an impact on intracranial disease.

"Effectively treating and controlling cerebral metastases is key to the survival of the patient. Though patients may succumb to their extracranial melanoma disease, we must try to give those patients with cerebral metastases some level of cognitive brain function while their melanoma disease takes its natural course elsewhere. This is where the Gamma Knife can play a decisive role in improving the quality of life," Dr. Izard says.