Room: Exhibit Hall | Forum 9
Purpose: To evaluate weighted logarithmic subtraction (WLS) method of dual-energy (DE) imaging using an on-board imager (OBI) across multiple commercial linear accelerators.
Methods: A study was conducted to evaluate bone suppression capabilities using a DE imaging on multiple linacs. The optimal weighting factor for WLS is utilized to characterize the sensitivity of DE imaging across different machines. A custom phantom consisting of 16 cm lung-equivalent material sandwiched between 2 cm tissue-equivalent slabs was utilized to simulate chest composition and optimize weighting factors. Five simulated tumors (0.5 â€“ 2.5 cm) were encased in the lung-equivalent compartment of the phantom and were overlapped with varying thicknesses of bone-equivalent material simulating ribs. The phantom was imaged at two different energies (120 and 60 kVp) on one Varian Edge and three True Beam linacs, enumerated as ED, TB-I, TB-II, and TB-III. Bone suppression was performed using WLS by minimizing the contrast between rib and neighboring soft-tissue regions. The optimal weighting factors across linacs were compared and relative tumor contrast was evaluated as a function of weighting factor.
Results: Higher weighting factors were observed when the thickness of overlapping bone increased. For 1.5, 3, 5 and 7 cm bone thicknesses, respective weighting factors were 0.533 Â± 0.002, 0.541 Â± 0.001, 0.547 Â± 0.02 and 0.553 Â± 0.05. The optimal weighting factors across linacs were 0.546 Â± 0.002, 0.535 Â± 0.002, 0.549 Â± 0.002 and 0.541 Â± 0.001, on TB-I, TB-II, TB-III and ED, respectively. Although, weighting factors showed slight variations across linacs relative tumor contrast was insensitive to these variations which was found to be < 1%.
Conclusion: We present a study to evaluate bone suppression capabilities using a DE imaging on multiple linacs. Weighting factors were consistent across multiple linacs producing equivalent tumor contrast.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA207483. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.