Radiosurgery for Metastases and Gliomas

Lars Leksell developed a system (Gamma Knife) to deliver high-dose irradiation to localized structures in the brain without the potential brain trauma associated with open surgery.
Multiple beams of ionizing radiation converge at one stereotactically defined point.
Precise selection of the targeted lesion with abrupt falloff and minimal trauma to surrounding tissue
Goal is the arrest of local tumor growth
Stereotactic radiosurgery: a high dose of radiation is usually delivered in a single fraction
- Utilizes a stereotactic localization system
Fractionated stereotactic radiotherapy: doses divided into multiple fractions separated by time to allow recovery of normal tissues
- Potential ability to target the tumor in multiple phases of the cell cycle

Indications

Single or multiple brain metastases, if tissue diagnosis is known and mass effect is medically controlled. Tumor types relatively “radioresistant” to conventional fractionated radiation therapy such as renal cell carcinoma often respond well to stereotactic radiosurgery.
Recurrent glioblastoma multiforme (GBM) in patients with Karnofsky > 70 following conventional radiation and chemotherapy, if a focal nodular recurrence is present
Does not treat invasive microscopic GBM; only targets focal limited area. Currently, there is insufficient evidence to make guidelines for the use of stereotactic radiosurgery or stereotactic fractionated radiation therapy in adult patients with malignant glioma.
Delicate locations including brain stem, deep white matter, or basal ganglia; also useful for tumors near anterior optic pathways (> 5 mm away).
Used in select patients who cannot tolerate surgery because of medical comorbidity
As stereotactic radiosurgery is applied in a single fraction, it is limited to smaller lesions to minimize the risk of radiation-induced toxicity.
Use generally limited to lesions up to 3 to 4 cm in maximum diameter