A novel tool for motion-related dose inaccuracies reduction in Tc-MAA SPECT/CT images for SIRT planning.

Introduction: In Selective Internal Radiation Therapy (SIRT), Y is administered to primary/secondary hepatic lesions. An accurate pre-treatment planning using Tc-MAA SPECT/CT allows the assessment of its feasibility and of the activity to be injected. Unfortunately, SPECT/CT suffers from patient-specific respiratory motion which causes artifacts and absorbed dose inaccuracies. In this study, a data-driven solution was developed to correct the respiratory motion.

Methods: The tool realigns the barycenter of SPECT projection images and shifts them to obtain a fine registration with the attenuation map. The tool was validated using a modified dynamic phantom with several breathing patterns. We compared the absorbed dose distributions derived from uncorrected(D)/corrected(D) images with static ones(D) in terms of γ-passing rates, 210 Gy isodose volumes, dose-volume histograms and percentage differences of mean doses (i.e., ΔD¯ and ΔD¯, respectively). The tool was applied to twelve SIRT patients and the Bland-Altman analysis was performed on mean doses.

Results: In the phantom study, the agreement between D and D was higher (γ-passing rates generally > 90%) than D and D. The isodose volumes in D were closer than D to D, with differences up to 10% and 30% respectively. A reduction from a median ΔD¯ = -19.3% to ΔD¯ = -0.9%, from ΔD¯ = -42.8% to ΔD¯ = -7.0% and from ΔD¯ = 1586% to ΔD¯ = 47.2% was observed in liver-, tumor- and lungs-like structures. The Bland-Altman analysis on patients showed variations (±50 Gy) and (±4 Gy) between D¯ and D¯ of tumor and lungs, respectively.

Conclusion: The proposed tool allowed the correction of Tc-MAA SPECT/CT images, improving the accuracy of the absorbed dose distribution.