Stereotactic radiosurgery and fractionated stereotactic radiotherapy: background, definitions, applications.

Stereotactic radiosurgery has emerged in recent years as a key treatment technique for a number of intracranial lesions, whether malignant or benign. In this issue of IMAJ, Attia and colleagues present a review of this treatment modality in general, as well as of their own experience [1]. The group from Sheba Medical Center is to be commended for their pioneering role in the introduction of this technology to Israel. Other groups include our own at Hadassah-Hebrew University Hospital, where we inaugurated a stereotactic radiosurgery program in March 2004. Based on our experience in Israel and earlier work in U.S. medical centers, as well as on literature in the field, we would like to discuss several terms and concepts that are relevant to radiosurgery and radiation therapy in general. We add a special focus on fractionated stereotactic radiotherapy, another valuable modality for treating various benign and malignant intracranial lesions. We also comment on the indications for radiosurgery and on treatment outcomes as presented by Attia et al. in their review. Radiation therapy plays a crucial role in the management of a variety of benign and malignant intracranial tumors. The goal of radiotherapy is to deliver a therapeutic dose to all neoplastic or abnormal cells while preserving normal neural tissue [2]. The concept of protracted radiation treatment using a low dose or multiple small fractions was developed based on animal studies and clinical experience over the past 75 years [3]. Today conventional radiotherapy uses multiple fractions over a period of weeks to permit lesion obliteration, with minimal damage to normal tissue during and after the course of treatment. Typically , conventional radiotherapy delivers photons to a target area in the brain, including a margin surrounding the lesion, with dose falloff outside the target volume. Stereotactic radiosurgery, a term introduced by Lars Leksell in 1951, refers to a single fraction of high dose irradiation delivered to a limited target volume of tissue with sharp dose falloff beyond the target. This technique was developed initially as a non-invasive approach for functional neurosurgical procedures, with radiation directed to targets only a few millimeters in diameter. Leksell believed that interruption of neural pathways might be beneficial in treating epilepsy and Parkinson disease. Today, target location in SRS is defined by image-guided stereo-taxy. A large single fraction is delivered by means of multiple, collimated beams. This large dose of irradiation is sufficient to produce focal, irreparable damage …