The mixed era of stereotactic radiosurgery and radiotherapy

Abstract

Since the introduction of radiosurgery by Leksell in 1951 [1], stereotactic radiosurgery (SRS) with delivery of a high dose of radiation in a single session has been used for the treatment of lesions in the brain and spine [2]. He developed the first commercially available dedicated radiosurgical device called the “Gamma Knife” (GK) in 1968. This machine made it possible to precisely deliver a single, large dose of highly conformal radiation to any number of intracranial sites using 201 fixed cobalt sources aimed at a center point. Since he coined the term “stereotactic radiosurgery”, 330 centers of GK radiosurgery in 54 countries currently treat a total of 80,000 new patients each year. Through approximately 70 years of SRS experience that began with GK radiosurgery, the role of radiosurgery has expanded to a wide variety of benign brain tumors, arteriovenous malformations, functional disorders (trigeminal neuralgia, movement disorder, epilepsy, and pain), and malignant brain tumors. On the other hand, radiation oncologists were unfamiliar with SRS such as highdose irradiation. They did not believe in the effectiveness of high-dose irradiation of the body from a radiobiological perspective, and were even concerned that radiation side effects would increase. These physicians had been treating with fractionated radiotherapy (RT) to reduce radiation side effects and planning target volume margins to minimize treatment uncertainty, as they were in an era of undeveloped imaging techniques. However, advances in radiotherapeutic and radioimaging technology have eliminated uncertainty in precision and high-dose radiation therapy. Subsequently, stereotactic body radiotherapy (SBRT) was derived from SRS with improvements in radiation technology, using a small number of fractions with a high degree of precision within the body, unlike traditional fractionated RT [3]. The terms “SRS” and “SBRT” were used for central nervous system (CNS) and non-CNS anatomic sites, respectively, and in both cases involve the delivery of a Received: May 25, 2021 Accepted: June 9, 2021