Medical Physics Letter A novel digital tomosynthesis „DTS… reconstruction method using a deformation field map Lei Ren a Department of Radiation Oncology, Duke University Medical Center, DUMC Box 3295, Durham, North Carolina, 27710 and Duke Medical Physics Graduate Program, 2424 Erwin Road Suite 101, Durham, North Carolina 27705 Junan Zhang, Danthai Thongphiew, and Devon J. Godfrey Department of Radiation Oncology, Duke University Medical Center, DUMC Box 3295, Durham, North Carolina 27710 Q. Jackie Wu, Su-Min Zhou, and Fang-Fang Yin Department of Radiation Oncology, Duke University Medical Center, DUMC Box 3295, Durham, North Carolina, 27710 and Duke Medical Physics Graduate Program, 2424 Erwin Road Suite 101, Durham, North Carolina 27705 Received 21 April 2008; revised 20 May 2008; accepted for publication 20 May 2008; published 13 June 2008 We developed a novel digital tomosynthesis DTS reconstruction method using a deformation field map to optimally estimate volumetric information in DTS images. The deformation field map is solved by using prior information, a deformation model, and new projection data. Patients’ previous cone-beam CT CBCT or planning CT data are used as the prior information, and the new patient volume to be reconstructed is considered as a deformation of the prior patient volume. The defor- mation field is solved by minimizing bending energy and maintaining new projection data fidelity using a nonlinear conjugate gradient method. The new patient DTS volume is then obtained by deforming the prior patient CBCT or CT volume according to the solution to the deformation field. This method is novel because it is the first method to combine deformable registration with limited angle image reconstruction. The method was tested in 2D cases using simulated projections of a Shepp–Logan phantom, liver, and head-and-neck patient data. The accuracy of the reconstruction was evaluated by comparing both organ volume and pixel value differences between DTS and CBCT images. In the Shepp–Logan phantom study, the reconstructed pixel signal-to-noise ratio PSNR for the 60° DTS image reached 34.3 dB. In the liver patient study, the relative error of the liver volume reconstructed using 60° projections was 3.4%. The reconstructed PSNR for the 60° DTS image reached 23.5 dB. In the head-and-neck patient study, the new method using 60° pro- jections was able to reconstruct the 8.1° rotation of the bony structure with 0.0° error. The recon- structed PSNR for the 60° DTS image reached 24.2 dB. In summary, the new reconstruction method can optimally estimate the volumetric information in DTS images using 60° projections. Preliminary validation of the algorithm showed that it is both technically and clinically feasible for image guidance in radiation therapy. © 2008 American Association of Physicists in Medicine. DOI: 10.1118/1.2940725 Key words: digital tomosynthesis, image reconstruction, deformable registration, image guided radiation therapy, cone-beam CT, prior information I. INTRODUCTION On-board cone beam CT CBCT is now becoming a pow- erful tool for image-guided radiation therapy, 1–4 but its clini- cal utility may be limited due to long acquisition time 1 min, high imaging dose to the patient 2–9 cGy, 5 and potential mechanical constraints 360° gantry rotation clear- ance. Alternatively, digital tomosynthesis DTS is a quasi- three-dimensional 3D imaging technique which recon- structs images from a limited angle of projections with shorter acquisition time 10 s, lower imaging dose 1 cGy, and less mechanical constraint 60° gantry rotation. 6,7 These features could be extremely beneficial for imaging organs affected by respiratory motions and for those patient treatments when a full gantry rotation is mechanically impossible. 8 Our previous studies have shown that registra- tion between reference and on-board DTS images recon- structed by the filtered back projection FBP method is able to provide accurate rigid body alignment of the patient’s bony structures. 9–12 However, DTS images reconstructed by the conventional FBP method have low plane-to-plane resolution, and they do not provide full volumetric information for target localiza- 3110 3110 Med. Phys. 35 „7…, July 2008 0094-2405/2008/35„7…/3110/6/$23.00 © 2008 Am. Assoc. Phys. Med.