What is the role of stereotactic radiosurgery in the treatment of brain metastasis?

Updated: Aug 01, 2018
  • Author: Victor Tse, MD, PhD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

This modality makes use of multiple, well-collimated beams converging on a small lesion with a steep dose gradient at the edge of the beam. This conformity allows a high dose of radiation to be delivered to the target in a single fraction without causing excessive radiation damage to surrounding healthy brain. Several lesions can theoretically be treated on a single clinic visit. As the number of lesions increase, the overlapping of fields exceeds tolerance of healthy brain to radiation injury. For lesions 1-3 cm, the median dose is 15-24 Gy.

Stereotactic radiosurgery is a more preferred treatment modality for radio-resistant lesions such as nonsmall cell lung cancer, renal cell carcinoma, and melanoma. It is also more frequently used to treat the resection cavity of brain metastasis, particularly in patients with breast metastatic disease. The latter population of patients has a higher survival potential, thus whole brain radiation or EBRT, with their long-term cognitive adverse effects, make these modalities a less favorable choice.

Median survival after radiosurgery is 14.1 months. Twenty-four percent of patients with brain metastasis from breast cancer have 24-month overall survival. The overall control rate in breast metastasis in the brain is 82-90%. Unfortunately, 47% of the patients have new brain metastasis 11-15 months after initial radiosurgery. This is especially true in melanoma. The median tumor control for most brain metastasis is about 10 months.

The size of metastatic tumors may not change until months after radiation. The lesion may appear to grow slightly immediately after treatment. Treatment can worsen peritumoral edema, which can be controlled with a prolonged course of high-dose steroids. The prophylactic use of anti-inflammatory drugs to reduce edema is still being debated. If cerebral edema becomes symptomatic, then craniotomy and resection is warranted.

Acute reactions due to edema occur within 2 weeks in 7-10% of patients. These reactions include headache, nausea, vomiting, worsening of preexisting neurological deficits, and seizure. Radiation necrosis happens later, 6 months after treatment in 4% of patients. It can manifest as a transient increase in tumor size, edema, or mass effect with or without frank necrosis. It can be difficult to distinguish from the tumor itself.

In a recent study, the radiation complication rate for stereotactic radiosurgery in treating metastatic brain tumors is estimated to be 6%. It has been shown that the risk of having imaging-documented radiation necrosis is proportional to the volume of nontumor brain tissue exposed to 10 or 12 Gy of radiation. For volume more than 10 cm3 in a single session of radiosurgery, the risk of necrosis is 47% and is about 24% when the volume is less than 10 cm3. [18] Fortunately, only 5.8% of the patients are symptomatic.

Collectively, these merging data confirm that radiosurgery is equally effective in treating brain metastasis. Radiosurgery is particularly useful in treating patients with limited systemic disease and higher Karnofsky scores and in patients with life expectancies of more than 6 months. However, radiosurgery is now commonly offered to patients with higher systemic tumor burden when a shorter treatment regimen is more desirable.

Radiosurgery is also increasingly used as the adjuvant therapy in patients who have undergone metastatic brain-tumor resection. The effectiveness of this treatment depends on the histology of the tumor.


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