TITLE:
Spine Stereotactic Body Radiation Therapy Residual Setup Errors and Intra-Fraction Motion Using the Stereotactic X-Ray Image Guidance Verification System
AUTHORS:
Kosj Yamoah, Nicholas G. Zaorsky, Joshua Siglin, Wenyin Shi, Maria Werner-Wasik, David W. Andrews, Adam P. Dicker, Voichita Bar-Ad, Haisong Liu
KEYWORDS:
Spine Stereotactic Body Radiotherapy; Immobilization; Intrafraction Motion
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.3 No.1,
January
27,
2014
ABSTRACT:
Purpose: To
determine the precision of our institution’s current immobilization devices for
spine SBRT, ultimately leading to recommendations for appropriate planning
margins. Methods: We identified 12 patients (25 treatments) with spinal
metastasis treated with spine Stereotactic Body Radiation Therapy (SBRT). The
Body-FIX system was
used as immobilization device for thoracic (T) and lumbar (L) spine lesions.
The head and shoulder mask system was used as immobilization device for
cervical (C) spine lesions. Initial patient setup used the infrared positioning
system with body markers.
Stereotactic X-ray imaging was then performed and correction was made if the
initial setup error exceeded predetermined institutional tolerances, 1.5 mm for
translation and 2° for rotation. Three additional sets of verification X-rays
were obtained pre-, mid-, and post-treatment for all treatments. Results: Intrafraction motion
regardless of immobilization technique was found to be 1.28 ± 0.57 mm. The mean
and standard deviation of the variances along each direction were as follows:
Superior-inferior, 0.56 ± 0.39 mm and 0.77 ± 0.52 mm, (p = 0.25); Anterior-posterior, 0.57 ± 0.43 mm and 1.14 ± 0.61 mm, (p = 0.01);
Left-right, 0.48 ± 0.34 mm and 0.74 ± 0.40 mm, (p = 0.09) respectively. There was a significantly greater difference in the average 3D variance
of the BodyFIX as compared to the head and shoulder mask immobilization system,
1.04 ± 0.46 mm and 1.71 ± 0.52 mm; (p = 0.003) respectively. Conclusions: Overall, our institution’s image guidance
system using stereotactic X-ray imaging verification provides acceptable
localization accuracy as previously defined in the literature. We observed a
greater intrafraction motion for the head and shoulder mask as compared with
the BodyFIX immobilization system, which may be a result of greater C-spine
mobility and/or the suboptimal mask immobilization. Thus, better immobilization
techniques for C-spine SBRT are needed to reduce setup error and intrafraction
motion. We are currently exploring alternative C-spine immobilization
techniques to improve set up accuracy and decrease intrafraction motion during
treatment.