Brachytherapy, the surgical implantation of radioactive isotopes into a tumor, is a conformal irradiation technique that can deliver high doses of radiation to well-defined brain tumors measuring less than 5 to 6 cm in diameter. Because of rapid dose fall-off, the tumor receives much higher doses of radiation than the surrounding normal brain tissue. Brachytherapy can be used as a primary treatment, as an adjunct to conventional radiation therapy, or as a treatment for recurrent lesions.

Brachytherapy was first used for brain tumors in the early 1900s.<sup>14 Frazier C.H. The effects of radium emanations upon brain tumors Surg Gynecol Obstet 1920 ;  31 : 236-239

Cliccare qui per andare alla sezione Riferimenti</sup> The stereotactic headframe developed by Leksell in the 1950s allowed greater precision in placing isotopes.<sup>24 Leksell L. The stereotactic apparatus for intracerebral surgery Acta Chir Scand 1951 ;  102 : 316-319

Cliccare qui per andare alla sezione Riferimenti</sup> The development of computerized tomography (CT) in 1974 and magnetic resonance (MR) imaging in 1982 further improved accuracy. The development of afterloading devices for radiation delivery has facilitated radiation protection and improved dosimetry. In recent years, the success of minimally invasive and noninvasive radiosurgical techniques have somewhat reduced the use of brachytherapy; nevertheless, good clinical results and a pressing need to improve treatment of brain tumors have continued to stimulate interest in this treatment modality.

Brachytherapy for brain tumors can be divided into three broad categories: low dose rate (LDR), high dose rate (HDR), and intracavitary (Table 1). In LDR brachytherapy, the radioactive sources, either permanent or temporary, are typically placed in catheters spaced evenly within the tumor or in the center of the tumor to deliver 5 to 60 cGy/hr. This may be done as an outpatient procedure, or it may require hospital admission. Another approach to permanent interstitial implants involves sewing or gluing iodine-125 (I-125) sources imbedded in suture material directly into a tumor cavity.<sup>18 Gutin P.H., Steven A.L., Hosobuchi Y. , e al. Brachytherapy of recurrent tumors of the skull base and spine with iodine-125 sources Neurosurg 1987 ;  20 : 938-945  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> In HDR brachytherapy, a dose rate of 100 to 200 cGy/min is delivered through temporary catheters placed evenly within the tumor or centrally using a device with high-activity radioactive sources that are temporarily inserted into the catheters. This procedure can be performed on either an inpatient or, more frequently, on an outpatient basis. Intracavitary brachytherapy is used to treat cystic tumors. The intralesional fluid is drained stereotactically, and an aqueous radioactive isotope is returned into the cyst cavity to release radiation over the lifetime of the isotope. Table 2 summarizes some of the potential advantages and disadvantages of permanent and temporary brain implants.

This article discusses the radiobiology of brachytherapy for brain tumors, describes the therapeutic procedures used at the Cleveland Clinic, and reviews some of the literature on brachytherapy for primary and recurrent astrocytomas, meningiomas, brain metastases, and pediatric tumors.