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