Stereotactic Body Radiotherapy for the Treatment of Spinal Metastases: An Overview of the University of Toronto, Sunnybrook Health Sciences Odette Cancer Centre, Technique

Abstract

Conventional low-dose radiation therapy (RT) has long been used in the treatment of patients suffering from the symptoms of metastatic cancer in and around the spine. The goals of therapy include pain control and at least short-term local disease control. Most patients are offered palliative doses such as 8 Gy in one fraction, 20 Gy in five fractions, or 30 Gy in 10 fractions, and as yet there has been no dose–response relationship within conventional RT practice. Stereotactic body radiation therapy (SBRT) is a relatively new technique that overcomes the previous limitations of conventional RT by delivering high biologically effective doses (BED), in the range of what is considered locally curative, using intensity-modulated radiotherapy (IMRT). Doses such as 16–24 Gy in a single fraction, 24–30 Gy in two or three fractions, and 30–40 Gy in four or five fractions are commonly used in spine SBRT, while sparing the surrounding normal tissues to a much lower dose that falls within tolerance. The high precision required for spine SBRT demands near-rigid patient immobilization, visualization of the target volume and spinal cord with magnetic resonance imaging, and image-guided radiotherapy. Ultimately, an overall delivery precision of approximately 1.5-2 mm is required for safe and effective treatment. The aim of this review is to discuss the technical delivery of spine SBRT with particular attention to the incorporation of robotic treatment couch technology. The HexaPOD (Elekta AB, Stockholm, Sweden) is the robotic couch in use at the University of Toronto, and it is capable of performing fine translations and rotations allowing for six degrees of freedom patient positioning. This technology is a major advancement in correcting patient setup errors.