title: Prospective evaluation of dual-energy imaging in patients undergoing image guided radiation therapy for lung cancer: initial clinical results.
abstract: OBJECTIVE
  A prospective feasibility study was conducted to investigate the utility of dual-energy (DE) imaging compared to conventional x-ray imaging for patients undergoing kV-based image guided radiation therapy (IGRT) for lung cancer.
  
  
  METHODS
  An institutional review board-approved feasibility study enrolled patients with lung cancer undergoing IGRT and was initiated in September 2011. During daily setup, 2 sequential respiration-gated x-ray images were obtained using an on-board imager. Imaging was composed of 1 standard x-ray image at 120 kVp (1 mAs) and a second image obtained at 60 kVp (4 mAs). Weighted logarithmic subtraction of the 2 images was performed offline to create a soft tissue-selective DE image. Conventional and DE images were evaluated by measuring relative contrast and contrast-to-noise ratios (CNR) and also by comparing spatial localization, using both approaches. Imaging dose was assessed using a calibrated ion chamber.
  
  
  RESULTS
  To date, 10 patients with stage IA to IIIA lung cancer were enrolled and 57 DE images were analyzed. DE subtraction resulted in complete suppression of overlying bone in all 57 DE images, with an average improvement in relative contrast of 4.7 ± 3.3 over that of 120 kVp x-ray images (P<.0002). The improvement in relative contrast with DE imaging was seen for both smaller (gross tumor volume [GTV] ≤5 cc) and larger tumors (GTV >5 cc), with average relative contrast improvement ratios of 3.4 ± 4.1 and 5.4 ± 3.6, respectively. Moreover, the GTV was reliably localized in 95% of the DE images versus 74% of the single energy (SE images, (P=.004). Mean skin dose per DE image set was 0.44 ± 0.03 mGy versus 0.43 ± 0.03 mGy, using conventional kV imaging parameters.
  
  
  CONCLUSIONS
  Initial results of this feasibility study suggest that DE thoracic imaging may enhance tumor localization in lung cancer patients receiving kV-based IGRT without increasing imaging dose.
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Tracy
authors.initials: T
authors.lastname: Sherertz
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Mark
authors.initials: M
authors.lastname: Hoggarth
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Jason
authors.initials: J
authors.lastname: Luce
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Alec M
authors.initials: AM
authors.lastname: Block
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Suneel
authors.initials: S
authors.lastname: Nagda
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Harkenrider
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois.
authors.forename: Bahman
authors.initials: B
authors.lastname: Emami
authors.affiliation: Department of Radiation Oncology, Loyola University Medical Center, Maywood, Illinois. Electronic address: jroeske@lumc.edu.
authors.forename: John C
authors.initials: JC
authors.lastname: Roeske
mesh_terms: D000368:Aged; D001842:Bone and Bones / Q000000981:diagnostic imaging; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D011446:Prospective Studies; D011829:Radiation Dosage; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012867:Skin / Q000528:radiation effects; D047368:Tumor Burden