Dual energy imaging using a clinical on-board imaging system

Abstract

Dual energy (DE) imaging consists of obtaining kilovoltage (kV) x-ray images at two different diagnostic energies and performing a weighted subtraction of these images. A third image is then produced that highlights soft tissue. DE imaging has been used by radiologists to aid in the detection of lung malignancies. However, it has not been used clinically in radiotherapy. The goal of this study is to assess the feasibility of performing DE imaging using a commercial on-board imaging system. Both a simple and an anthropomorphic phantom were constructed for this analysis. Planar kV images of the phantoms were obtained using varied imaging energies and mAs. Software was written to perform DE subtraction using empirically determined weighting factors. Tumor detectability was assessed quantitatively using the signal-difference-tonoise ratio (SDNR). Overall DE subtraction suppressed high density objects in both phantoms. The optimal imaging technique, providing the largest SDNR with a dose less than our reference technique was 140 kVp, 1.0 mAs and 60 kVp, 3.2 mAs. Based on this analysis, DE subtraction imaging is feasible using a commercial on-board imaging system and may improve the visualization of tumors in lung cancer patients undergoing image-guided radiotherapy.

Evaluation of a template-based algorithm for markerless lung tumour localization on single- and dual-energy kilovoltage images

“…Energies for DE imaging were selected based on previous studies where image quality and dose were optimized. 30,[43][44][45] A prior study demonstrated that the estimated mean dose at the skin per DE image pair was approximately 0.44 6 0.03 mGy, comparable with the expected skin dose from conventional SE imaging. 30 Image pairs were acquired once per treatment fraction with a maximum of five sets per patient.…”

“…Using these images, a weighted logarithmic subtraction is performed that removes obscuring bony anatomy (ribs and vertebral bodies), thus creating a third image that highlights soft tissue, such as lung tumours. 30,43,44 Recently, Sherertz et al 30 published a prospective feasibility study investigating tumour visibility in DE radiographs compared with conventional kV radiographs used in image-guided radiation therapy of patients with lung cancer. In that study, obscuring bony anatomy was successfully removed in all analyzed DE images, and tumour visibility was improved when compared with conventional radiographs.…”

Feasibility of markerless tumor tracking by sequential dual-energy fluoroscopy on a clinical tumor tracking system

“…Improved contrast of lung lesions after DE subtraction, resulting in significant improvement in markerless tumor localization, has been reported by several groups [16][17][18][19]. In this study, we evaluate the feasibility of markerless tumor tracking through the implementation of DE subtraction imaging into the current clinical RTTT workflow, using the implanted fiducials as a benchmark.…”

Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

“…The optimal weighting factor value was iteratively determined by calculating the signal difference ( ΔS R ) between the background signal and the signal of each material (Hoggarth et al 2013)…”

“…Hoggarth et al (2013) used dual-energy to subtract bone for improved soft-tissue and tumor visualization during image-guided lung radiotherapy. In a subsequent study they used their technique for markerless motion tracking of lung tumors with dual-energy fluoroscopy (Patel et al 2015).…”