Positional Accuracy of Treating Multiple Versus Single Vertebral Metastases With Stereotactic Body Radiotherapy.

The aim of this study is to determine whether stereotactic body radiotherapy for multiple vertebral metastases treated with a single isocenter results in greater intrafraction errors than stereotactic body radiotherapy for single vertebral metastases and to determine whether the currently used spinal cord planning organ at risk volume and planning target volume margins are appropriate. Intrafraction errors were assessed for 65 stereotactic body radiotherapy treatments for vertebral metastases. Cone beam computed tomography images were acquired before, during, and after treatment for each fraction. Residual translational and rotational errors in patient positioning were recorded and planning organ at risk volume and planning target volume margins were calculated in each direction using this information. The mean translational residual errors were smaller for single (0.4 (0.4) mm) than for multiple vertebral metastases (0.5 (0.7) mm; P = .0019). The mean rotational residual errors were similar for single (0.3° (0.3°) and multiple vertebral metastases (0.3° (0.3°); P = .862). The maximum calculated planning organ at risk volume margin in any direction was 0.83 mm for single and 1.22 for multiple vertebral metastases. The maximum calculated planning target volume margin in any direction was 1.4 mm for single and 1.9 mm for multiple vertebral metastases. Intrafraction errors were small for both single and multiple vertebral metastases, indicating that our strategy for patient immobilization and repositioning is robust. Calculated planning organ at risk volume and planning target volume margins were smaller than our clinically employed margins, indicating that our clinical margins are appropriate.

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

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.