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From Treatment Beam Delivery to Real-Time Volumetric Imaging

M Chen

M Chen*, T Rozario , W Lu , UT Southwestern Medical Center, Dallas, TX


SU-K-601-6 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 601

Purpose: Real-time patient volumetric imaging is essential for precise radiation beam targeting and dose reconstruction. The commonly used surrogates, such as video imaging, may not correlate with tumor positions or volumetric information. KV beam imaging allows computer tomographic (CT) image reconstruction, but frequent kV irradiations are prohibitive to avoid patient overdose. We have proposed a real-time volumetric imaging strategy using the treatment beams (MV) and kV beams when triggered and put it into tests in this research.

Methods: The proposed strategy uses the electronic portal image device (EPID) to acquire projection images of treatment beams and kV beams when triggered and compares them with pre-calculation. Pre-calculation includes both treatment beam and kV beam in-transit projection images (MVDRR and kVDRR) at each beam angle for each phase in 4DCT. The mean projection of all phases is subtracted from the projection of each phase to enhance image contrast. Transition phases are simulated or acquired to establish distributions of phase correlations and further the threshold and accuracy rate correspondence for phase identification.Real time MV images are compared against pre-calculated MVDRR using correlation. If the correlation does not meet the given threshold, kV projections will be triggered. If neither MV nor kV projections hold sufficient confidence, prediction will kick off by extrapolating correlations and motion patterns.

Results: A lung phantom with a movable tumor target was used for simulating projections. Sufficient contrast was demonstrated after subtracting the mean projection. The accuracy rate for phase identification was above 90%, except when motion was in the beam direction. For those unfavorable treatment beam angles, complementary information provided by kV projections kicks in and improved the accuracy.

Conclusion: Phantom studies showed the feasibility of the proposed strategy. Enhancing the contrast of the projection image is a key factor in improving the success rate.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by Varian through a Master Research Agreement.

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