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Spine Stereotactic Body Radiation Therapy Residual Setup Errors and Intra-Fraction Motion Using the Stereotactic
Kosj Yamoah1, Nicholas G Zaorsky1,2, Joshua Siglin1
1Department of Radiation Oncology, Jefferson Medical College and Kimmel Cancer Center of Thomas Jefferson University, Philadelphia, USA.
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology
|January 16, 2018
Summary
Spine Stereotactic Body Radiation Therapy (SBRT) immobilization accuracy was assessed. The head and shoulder mask showed greater intrafraction motion than the BodyFIX system, indicating a need for improved cervical spine immobilization techniques.
Area of Science:
- Radiation Oncology
- Medical Physics
- Spinal Imaging
Background:
- Spine Stereotactic Body Radiation Therapy (SBRT) requires precise immobilization for accurate dose delivery.
- Current institutional immobilization devices include the Body-FIX system and head and shoulder masks.
Purpose of the Study:
- To evaluate the precision of current immobilization devices for spine SBRT.
- To inform recommendations for appropriate planning margins in spine SBRT.
Main Methods:
- 12 patients with spinal metastasis undergoing SBRT were analyzed (25 treatments).
- Body-FIX used for thoracic/lumbar spine; head/shoulder mask for cervical spine.
- Stereotactic X-ray imaging and infrared positioning system used for setup verification and correction.
Main Results:
- Intrafraction motion averaged 1.28 ± 0.57 mm across all techniques.
- The head and shoulder mask system demonstrated significantly greater 3D variance (1.71 ± 0.52 mm) compared to Body-FIX (1.04 ± 0.46 mm).
- Significant differences in variance noted in the anterior-posterior direction (p=0.01).
Conclusions:
- The institution's image guidance system provides acceptable localization accuracy for spine SBRT.
- The head and shoulder mask system exhibits greater intrafraction motion, potentially due to C-spine mobility or suboptimal mask fit.
- Improved immobilization techniques for cervical spine SBRT are necessary to reduce setup errors and intrafraction motion.
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