Stereotactic Radiosurgery or Gamma Knife Surgery (GKS)
Stereotactic radiosurgery is a neurosurgical procedure in which high-dose radiation is targeted at the HH tumor from multiple directions, resulting in minimal radiation exposure to normal surrounding tissue. It is noninvasive (performed without opening the skull) and there is no pain or sensation from the treatment (with the exception of discomfort from the placement of a stereotactic guidance frame on the head).
Gamma Knife Surgery (GKS) has been used worldwide for other brain tumors and abnormalities and the side effects of radiosurgery are believed to be rare, transient, and in most cases very predictable. GKS is usually considered as an option for small, deeply seated lesions where there is an increased risk of complications or functional worsening with the more invasive resective surgeries. In these types of cases, GKS is a good first option in terms of safety, effectiveness and also cost (important to many insurance companies).
Many medical centers using Gamma Knife focus treatments on the top and sides of the hamartoma. In order to maximize effectiveness and minimize risk to the optic nerves, treatment centers will often treat the critical upper portion of the hamartoma with the higher dose while limiting the dose as it gets closer to the lower portion, closer to the optic nerve. Studies have shown that treatments with less than 17-18 Gy have been less effective overall. Individuals who have shown improvement after Gamma Knife treatment have usually received a dose of 17-18 gray (Gy) to the edge of the hamartomas. To minimize risk of vision loss when the bottom of the hamartoma is near the optic nerves, the radiation level in this area may be limited to 12 Gy.
The advantages associated with GKS include avoiding the risks associated with surgical resection, including short-term memory problems, hypothalamic dysfunction, and bleeding. However, a disadvantage of radiosurgery is its delayed onset of action. It is not uncommon to wait 6 months to 18 months (for some, even up to 3 years) to realize the full effects of the treatment. For some individuals, repeat radiation may be required to get the desired effects. If GKS proves unsuccessful, standard surgery may still be an option. For a list of questions to ask your surgeon if you are contemplating GKS surgery, click here.