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Evaluating the Dosimetric Accuracy of Extended Field-Of-View CT Reconstructions Using Clinical Data with Real Patient Geometries

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E Shugard

E Shugard1*, N Mistry2 , J Cheung3 , J Pouliot4 , J Chen5, (1, 3-5) University of California San Francisco, San Francisco , (2) Siemens Healthcare USA, Malvern, PA


SU-F-207-9 (Sunday, July 12, 2015) 4:00 PM - 6:00 PM Room: 207

Purpose: To determine the accuracy of dose calculations performed with CT images reconstructed using extended field of view (FOV) algorithms.

Methods: In this study we selected 6 radiotherapy patients (3 head and neck & 3 chest/pelvis) whose body circumferences extended past the 50 cm scan FOV in the treatment planning CT. Images acquired on a Siemens Sensation Open scanner, were reconstructed using the standard FOV (sFOV) and two different extended FOV algorithms, eFOV and HDFOV. A physician and dosimetrist identified the radiation target, critical organs, and external patient contour. A benchmark CT was created for each patient, consisting of an average of the 3 CT reconstructions with a density override applied to regions containing truncation artifacts, and was used to create an optimal radiation treatment plan. The plan was copied onto each reconstruction without density override and dose was recalculated.

Results: The native sFOV dose calculations had the largest deviation from the benchmark (0.4 – 6.0%). Both the HDFOV and eFOV calculations showed improvement over the sFOV. For patients with a smooth patient contour, the HDFOV calculation had the least deviation from the benchmark (0.1-0.5%) compared to eFOV (0.4-1.8%). In cases with large amounts of tissue and irregular skin folds, the eFOV deviated the least from the benchmark (0.2-0.6%) compared to HDFOV (1.3-1.8%). It was observed that the eFOV scan has large image artifact in air with an average HU of -600 compared to the ideal of -1000. In these cases, the artifact in air appears to attenuate the dose and compensate for the missing tissue density. The HDFOV demonstrated minimal artifact in air.

Conclusion: Both eFOV and HDFOV provide improved dose calculation accuracy. The HDFOV reconstruction provides a clearer patient border than the eFOV allowing for well-defined density overrides to be applied with minimal air artifact.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by Siemens Medical Solutions.

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