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Dosimetric Impact of CT Artifacts for Spine SBRT

M Bussiere1*, T Botticello1, J Daly2, A Schwartz1, K Oh1, J Daartz1, (1) Massachusetts General Hospital, Boston, MA, (2) Memorial Sloan Kettering Cancer Center, New York, NY

Presentations

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: Contouring implants and CT artifacts for spine stereotactic radiation therapy (SBRTs) planning can be a lengthy process. We assess the effort of hardware and artifact delineation against the dosimetric impact on target and organs at risk (OAR) with the goal of minimizing or eliminating the tasks required to apply density corrections. Prior to this study, our practice was to delineate and override artifacts for SBRTs.

Methods: 16 clinical cases were used to assess the impact of static (IMRT) vs arc (VMAT) delivery, contouring bias, metal artifact reduction software, and limitation of density corrections. DVH statistics were compared between clinical plans and those without overrides.

Results: Typical artifact contouring time was 120-180 minutes. Density corrections resulted in average dose differences in the vertebral body of 40cGy (2% prescription) to < 5cc and 80cGy (4% prescription) < 0.1cc, mostly adjacent to hardware and away from critical OAR. Critical organ dose differences were = 20cGy (1% prescription) to 0.1cc. Dark-artifacts, hardware, and using static field IMRT as a delivery technique resulted in larger dose differences than bright-artifacts and VMAT. Differences were larger than expected between dosimetrists’ contours. There were no observable dosimetric differences using artifact reduction software.

Conclusion: Presuming doses computed with artifact corrections are more representative of the actual delivery, eliminating the overrides generally resulted in higher OAR doses – therefore, clinical plans generated without corrections would be more conservative. This study indicates that for SBRTs cases with hardware distant to critical organs, there is minimal dosimetric impact and significant time savings by eliminating some, or all artifact contouring and density corrections.

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Keywords

Dosimetry, Image Artifacts, Tissue Density

Taxonomy

TH- External Beam- Photons: extracranial stereotactic/SBRT

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