Abstract
Objective
Precise tumor alignment is vital in lung stereotactic body radiotherapy (SBRT). Differences in center of mass (COM) resulting from mixing and matching target delineation methods, and planning image datasets could introduce systematic errors.
Methods
Thirty consecutive lung SBRT patients were simulated with free-breathing CT (FBCT), maximum inhalation and exhalation breath hold CT (BHCT), and 4D-CT. Four planning target volumes (PTV) were created: 5/10-mm expansion from the gross tumor volume (GTV) in FBCT (PTVFBCT), 5-mm expansion from the internal target volume (ITV) in BHCT (PTVBHCT), 5-mm expansion from the ITV in the maximum intensity projection (PTVMIP), and 5-mm expansion from the ITV in 4D-CT (PTV4D-CT). Using average intensity projection CT (AIP-CT) or FBCT as the reference images, PTVs were transferred after bony registration to compare COMs.
Results
When AIP-CT was used as reference, the mean COM vector shifts of the PTVFBCT, PTVBHCT, and PTV4D-CT were 2.94 mm (p = 0.0094), 4.35 mm (p = 0.0001), and 1.45 mm (p = 0.57), respectively, relative to the COM of the GTV on AIP-CT. When FBCT was used as reference, the mean COM vector shifts of the PTVBHCT, PTVMIP, and PTV4D-CT were 3.6 mm (p = 0.0006), 2.78 mm (p = 0.003), and 2.94 mm (p = 0.002) relative to the GTV on FBCT, respectively.
Conclusions
Depending on the reference images used, the COMs of the PTVFBCT, PTVBHCT, and PTV4D-CT are inconsistent, exhibiting significant shifts relative to each other. To avoid possible systematic localization errors, we recommend using 4D-CT/MIP for target delineation and AIP-CT for planning and alignment.
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Acknowledgments
We appreciate the assistance of Anthony Mastroianni, MD, and Lorelei Woody for their review of this manuscript.
Funding
No grant or additional financial support was received for this research.
Conflict of interest
Dr. Xia reports grants from Siemens Medical Solutions, grants from Philips Medical Systems, and grants from BrainLab, outside the submitted work. Dr. Woody, Dr. Djemil, Dr. Stephans, and Dr. Videtic declare that they have no conflicts of interest pertaining to the conduct of this research.
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Woody, N.M., Stephans, K.L., Videtic, G.M.M. et al. Systematic errors in lung stereotactic body radiation therapy (SBRT): a caution on mixing and matching target delineation methods and planning CTs. J Radiat Oncol 4, 185–191 (2015). https://doi.org/10.1007/s13566-015-0194-7
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DOI: https://doi.org/10.1007/s13566-015-0194-7