Abstract
Stereotactic body radiation therapy and stereotactic radiosurgery have become important treatment options for the treatment of spinal malignancies. A better understanding of dose tolerances with more conformal technology have allowed administration of higher and more ablative doses. In this review, the framework for approaching a patient with spinal metastases and primary tumors will be discussed as well as details on the delivery of this treatment.
Keywords: SBRT, spinal malignancies, tumor ablation, image-guided
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6198394/
Stereotactic Body Radiation Therapy for Spinal Malignancies
Re: Stereotactic Body Radiation Therapy for Spinal Malignancies
Introduction
Stereotactic body radiotherapy (SBRT) involves the precise delivery of high dose per fraction radiotherapy (RT) to extracranial tumors. Its predecessor, stereotactic radiosurgery (SRS) to the brain, was first described by Leksell in 1951 and utilized a collimator helmet rigidly fixed to the skull for precise target localization accuracy.1,2 Although the spine shares some advantages with the brain as a treatment target, SBRT did not emerge until around 40 years later due to limitations in immobilization and localization outside the cranium as well as treatment planning technology.3
An individual vertebral body, such as the skull, is a bony structure that experiences minimal interfraction change and little intrafraction movement, in contrast to less rigid sites such as the lung or gastrointestinal (GI) tract.4 Although early endeavors attempted the use of rigid, surgically implanted frames similar to brain SRS, physicians soon found that the spine lends itself well to X-ray, and more recently computed tomography (CT)-based, image guidance due to its irregular shape and contrast from surrounding soft tissues.5–7
The evolution of treatment planning technology has also been closely tied with the development of spine SBRT. Without the benefit of a helmet to focus numerous beams at a single, precise isocenter simultaneously, as in frame-based radiosurgery, safe delivery of doses to irregular structures such as the the spine requires utilization of multiple beam angles or arcs. Intensity-modulated RT, developed in the 1980s to 1990s, and more recently volumetric-modulated arc therapy (VMAT) in particular have allowed for more conformal dose planning than was previously possible with conventional linear accelerator-based treatment, allowing safe delivery of ablative doses while sparing the spinal cord and other neighboring structures.8 As a result, high-dose treatment can be delivered to the spine in short courses of 1 to 5 fractions, that is, SBRT, and is now used in a variety of clinical settings including for metastatic disease and primary tumors of the spine.
Stereotactic body radiotherapy (SBRT) involves the precise delivery of high dose per fraction radiotherapy (RT) to extracranial tumors. Its predecessor, stereotactic radiosurgery (SRS) to the brain, was first described by Leksell in 1951 and utilized a collimator helmet rigidly fixed to the skull for precise target localization accuracy.1,2 Although the spine shares some advantages with the brain as a treatment target, SBRT did not emerge until around 40 years later due to limitations in immobilization and localization outside the cranium as well as treatment planning technology.3
An individual vertebral body, such as the skull, is a bony structure that experiences minimal interfraction change and little intrafraction movement, in contrast to less rigid sites such as the lung or gastrointestinal (GI) tract.4 Although early endeavors attempted the use of rigid, surgically implanted frames similar to brain SRS, physicians soon found that the spine lends itself well to X-ray, and more recently computed tomography (CT)-based, image guidance due to its irregular shape and contrast from surrounding soft tissues.5–7
The evolution of treatment planning technology has also been closely tied with the development of spine SBRT. Without the benefit of a helmet to focus numerous beams at a single, precise isocenter simultaneously, as in frame-based radiosurgery, safe delivery of doses to irregular structures such as the the spine requires utilization of multiple beam angles or arcs. Intensity-modulated RT, developed in the 1980s to 1990s, and more recently volumetric-modulated arc therapy (VMAT) in particular have allowed for more conformal dose planning than was previously possible with conventional linear accelerator-based treatment, allowing safe delivery of ablative doses while sparing the spinal cord and other neighboring structures.8 As a result, high-dose treatment can be delivered to the spine in short courses of 1 to 5 fractions, that is, SBRT, and is now used in a variety of clinical settings including for metastatic disease and primary tumors of the spine.
Debbie