Reconstruction of the treatment area by use of sinogram in helical tomotherapy
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SHORT REPORT
Open Access
Reconstruction of the treatment area by use of sinogram in helical tomotherapy Akihiro Haga1*, Keiichi Nakagawa1, Calvin Maurer2, Ken Ruchala2, Edward Chao2, Dylan Casey2, Satoshi Kida1, Dousatsu Sakata1, Masahiro Nakano1, Taiki Magome1 and Yoshitaka Masutani1
Abstract Background: TomoTherapy (Accuray, USA) has an image-guided radiotherapy system with a megavoltage (MV) X-ray source and an on-board imaging device. This system allows one to acquire the delivery sinogram during the actual treatment, which partly includes information from the irradiated object. In this study, we try to develop image reconstruction during treatment with helical tomotherapy. Findings: Sinogram data were acquired during helical tomotherapy delivery using an arc-shaped detector array that consists of 576 xenon-gas filled detector cells. In preprocessing, these were normalized with full air-scan data. A software program was developed that reconstructs 3D images during treatment with corrections as; (1) the regions outside the field were masked not to be added in the backprojection (a masking correction), and (2) each voxel of the reconstructed image was divided by the number of the beamlets passing through its voxel (a ray-passing correction). The masking correction produced a reconstructed image, however, it contained streak artifacts. The ray-passing correction reduced this artifact. Although the SNR (the ratio of mean to standard deviation in a homogeneous region) and the contrast of the reconstructed image were slightly improved with the ray-passing correction, use of only the masking correction was sufficient for the visualization purpose. Conclusions: The visualization of the treatment area was feasible by using the sinogram in helical tomotherapy. This proposed method would be useful in the treatment verification. Keywords: Megavoltage CT, In-treatment CT, Image reconstruction during treatment, TomoTherapy®
Introduction As radiotherapy is complex, treatment verification becomes significant. The evaluation of the absorbed dose in phantoms is strongly recommended for all patients having intensity-modulated radiotherapy (IMRT) [1]. In addition, accuracy of the patient setup is more important in the IMRT than that in the conventional radiotherapy. Image-guided radiotherapy (IGRT) can entail correcting the patient position just prior to treatment by gathering information about anatomical locations during setup. IGRT can utilize various imaging technologies such as the portal images of the treatment beam [2-5], magnetic resonance imaging [6], ultrasound [7,8], and computed tomography (CT) [9,10].
* Correspondence: [email protected] 1 Department of Radiology, University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo, Tokyo, Japan Full list of author information is available at the end of the article
TomoTherapy® has an IGRT system with megavoltage (MV) X-ray source and an on-board imaging device [11]. With the MV CT, it became feasible to perform efficient daily-3D registration of the patient position before each
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