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Estimation of 3D Imaging Dose for KV-MV-STR CBCT

M Shi1,2*, M Jacobson2, M Myronakis2, D Ferguson2, M Lehmann3, P Baturin4, T Harris2, P Huber3, R Fueglistaller3, I Valencia Lozano2, C Williams2, D Morf3, R Berbeco2, (1) University of Massachusetts Lowell, Lowell, MA, (2) Brigham and Women's Hospital & Dana Farber Cancer Institute & Harvard Medical School, Boston, MA, (3) Varian Medical Systems, Baden, Switzerland, (4) Varian Medical Systems, Palo Alto, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: KV-MV scan time reduction (kV-MV-STR) is a cone-beam CT (CBCT) technique that reduces scan time by simultaneous acquisition with orthogonal kV and MV beams. Potential applications include breath-hold CBCT for motion management. However, the impact on dose of mixing an MV sub-arc with a kV sub-arc needs to be carefully evaluated along with image quality. This study compared the dose of conventional kV-CBCT with kV-MV-STR using Monte Carlo simulations.


Methods: A 200° kV-MV-STR scan of a digitized thorax phantom was simulated. The MV portion was simulated with a 2.5 MV source acquiring 181 projections over a 90° arc. The kV portion was simulated using a 125 kVp source acquiring 272 projections over the remaining 110° arc. Each projection was simulated with a number of primary photons equivalent to either 0.0025 MU for the MV arc or 1.5 mAs for the kV arc. A conventional kV-CBCT scan of the same thorax phantom was simulated using a 125 kVp source acquiring 498 projections over the same 200° total arc as kV-MV-STR. The phantom dose maps were recorded for both scans and compared. Measured versions of the simulated scans were also experimentally acquired on a Varian TrueBeam Linac equipped with a high-DQE four-layer imager. FDK reconstructions of the scans were compared. A previously proposed roughness-penalized beam hardening correction method was applied to the kV-MV-STR data set.


Results: The kV-MV-STR technique generally delivered lower dose than the kV-only scan. The dose in lung was 11.15 mGy for kV-MV-STR and 26.60 mGy for kV-CBCT, respectively. The heart dose was 21.37 mGy and 36.85 mGy, respectively. The reconstructed image quality for the two scans was comparable, with a minor reduction in bone contrast for kV-MV-STR.


Conclusion: With comparable image quality, kV-MV-STR delivers less dose to the lung and the heart while simultaneously reducing scan time.

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Funding Support, Disclosures, and Conflict of Interest: NIH/NCI R01CA188446

Keywords

Cone-beam CT, Dose, Monte Carlo

Taxonomy

IM/TH- Cone Beam CT: Monte Carlo modeling

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