Stereotactic radiosurgery for multiple brain metastases

Abstract

Stereotactic radiosurgery (SRS) alone has become one of the treatment options for patients with 1–4 metastases as the detrimental effects of whole brain radiation therapy on neurocognition and quality of life are becoming well known. Multiple randomized control trials also failed to show overall survival benefit of adding whole brain radiation therapy to SRS. However, the role of SRS in multiple brain metastases, especially those with ≥4 tumors, remains controversial. The literature is emerging, and the limited evidence suggests that the local control benefit is independent of the number of metastases, and that patients with more than four brain metastases have similar overall survival compared to those with 2–4 tumors. This review aims at summarizing the current evidence of SRS for multiple brain metastases, divided into limited (2–3) and multiple (≥4) lesions. It also reviews the technical aspects and cost–effectiveness of SRS.

Keywords::

• brain metastases
• gamma knife system
• neurocognitive function
• stereotactic radiosurgery
• whole brain radiation therapy

Financial & competing interests disclosure

S Lo has received travel expenses and honorarium from Varian Medical Systems and research support from Elekta AB. A Sahgal has received honorarium for educational seminars and research support for radiosurgery research by Elekta AB. EL Chang has received honorarium for educational seminars by Elekta AB. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Stereotactic radiosurgery (SRS) for brain metastases gives consistently high local control rates of approximately 70–90% at 1 year, with minimal acute side effects and a low risk of symptomatic radiation necrosis (<10%).

• Efficacy of SRS is considered to be equivalent to neurosurgical excision in lesions smaller than 3 cm in diameter.

• SRS alone for newly diagnosed, limited brain metastases (1–4) is associated with better preserved neurocognitive function and quality of life compared to SRS plus upfront WBRT.

• Patients who receive radiation treatments for brain metastases must be followed up by close surveillance with MRI as distant intracranial recurrence rates are high – consistently approximately 30–50% at 1 year. Repeating focal treatment either with SRS or surgical treatment was feasible in selected patients.

• Salvage treatment for symptomatic recurrence after SRS alone treatment is associated with worse outcomes than asymptomatic recurrence.

• There is adequately powered level II evidence showing that OS of patients with 2–4 brain metastases is similar to 5–10 metastases after SRS alone treatment, provided that the total tumor volume is less than 15 ml, the largest tumor is less than 10 ml or less than 3 cm in diameter, performance status of patients is ≥70 and there is no evidence of leptomeningeal metastases.

• Radiation dose to normal brain tissue with SRS is strongly associated with the number of brain metastases irradiated. Reduction in the prescription dose may be necessary to minimize the V12 volume (volume of normal brain receiving >12 Gy) to lower the risk of radiation necrosis.