Room: Exhibit Hall | Forum 5
Purpose: Dual-energy x-ray imaging with dual-filter was investigated for Brainlab ExacTrac clinical stereoscopic image guidance system to enhance soft-tissue-only image quality in SBRT applications. The main objective of this work was to establish an accurate computational method to identify optimal filter material for both low (LE) and high energy (HE) beams in compliance with systemâ€™s clinical operating constrains, including tube current, dynamic range of detector, scatter effect, and patient size.
Methods: Filter materials in atomic range 1-83 for LE and HE beams were investigated using SPEKTR 3 simulations based on spectral separation ratio metric, defined to quantify separation of HE and LE spectra. Clinical constraints were included. To this end, dynamic range of the flat panel and scatter effect were determined experimentally. The required mAs for each pair of filters was determined by 70% HE and 30% LE dose allocation and keeping the total patient dose to clinical single energy dose of 0.52mGy. Only those pairs of filters that met the dynamic range and mAs conditions were considered. Three different patient sizes were included. Various pairs of kVp were explored to achieve optimized results for all patient sizes.
Results: Considering all clinical conditions, [140,80] kVp was the optimal energy pair, 0.5mm â?µâ?¸Ce and 0.2mm Â²â?´Cr were the filter of choice for HE and LE beams, respectively. This resulted in the optimal highest spectra separation ratio of 1.69, which worked for small, medium and large patient sizes. The optimal HE and LE mAs were 75 and 35, respectively, which were well within the operating range of the ExacTrac.
Conclusion: The optimal beam filtration of stereoscopic x-ray imaging was identified for both HE and LE x-rays that ultimately could be confidently implemented in the clinic for the enhancement of dual-energy image quality and consequently tumor visualization during stereoscopic image guidance of radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: Atlantic Canada Opportunities Agency (ACOA), Atlantic Innovation Fund (AIF)