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On the Dosimetric Influence of Reference CT Selection for Patient Specific Quality Assurance Using the ArcCheck

U Robins

U Robins*, T Romaguera , D Wieczorek , V Mishra , A Gutierrez , Miami Cancer Institute, Miami, FL


SU-I-GPD-T-273 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: IMRT measurement devices used to validate patient specific treatment plans are commonly CT scanned so that a reference CT image can be used for planning. In doing so, many of these devices will induce artifacts in the reference CT due to their internal metallic construction. Two methods to overcome this are to use a synthetic CT (kVCT with density override) or the use of a MVCT. The purpose of this study was to quantify the dosimetric impact of using either a kVCT, synthetic CT, and MVCT as a reference CT data set for the ArcCheck system when performing IMRT QA.

Methods: Three different reference CT image sets of the ArcCheck system were acquired, namely a kVCT, synthetic CT (kVCT with density override), and a MVCT using the Radixact system. Three prostate patient treatment plans were mapped onto each of the three reference image sets. The doses were then calculated and exports to VelocityAI. The dose from the synthetic CT image set was used as a reference and the kVCT-based dose and MVCT-based dose was subtracted from the synthethic CT dose. In VelocityAI, an evaluation ROI enclosing the target was created and used to obtain statistics.

Results: Dosimetric differences in the synthetic dose were closer to the MVCT (0.9% SD 0.0025) than to the kVCT (2.7%, SD 2). The spread of the dose difference histogram between the kVCT and synthetic CT was larger than the MVCT and synthetic CT.

Conclusion: When using the ArcCheck platform for patient specific QA, the difference in using a kVCT, synthetic CT, or MVCT are minimal with regards to dose calculation. However, MVCT showed improved agreement to the synthetic CT than the kVCT.

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