Assessment of Spatial Uncertainties in the Radiotherapy Process With the Novalis System

Nagoya Radiosurgery Center, Nagoya Kyoritsu Hospital, Nagoya, Japan.
International journal of radiation oncology, biology, physics (Impact Factor: 4.26). 11/2009; 75(2):549-57. DOI: 10.1016/j.ijrobp.2009.02.080
Source: PubMed


The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX) system with statistical analysis retrospectively in order to determine the tolerance of systematic components of spatial uncertainties with the Novalis system.
Three factors of geometrical accuracy related to the ETX system were evaluated by phantom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, accuracy of the automated calculation by the image fusion algorithm in the patient registration software was evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the Novalis system was evaluated.
As to the location dependency of the detection ability of the infrared system, the detection errors between the actual position and the detected position were 1% in translation shift and 0.1 degrees in rotational angle, respectively. As to the accuracy of patient verification software, the repeatability and the coincidence of the calculation value by image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the ETX isocenter and the mechanical isocenter was 0.313 +/- 0.024 mm, in a suitable procedure.
The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient setup, and daily quality assurance for the Novalis system are achieved in the routine workload.

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Available from: Tatsuya Kobayashi, Jul 16, 2014
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    • "are indispensable [9] [10], in addition to the uncertainty for target localization such as the accuracy of CT-MRI fusion. These parameters include the shift in position among the MV isocenter, center of room lasers and central point detected with the ExacTrac system, the uncertainty of the MV isocenter position with gantry and couch rotation , the uncertainty of the ExacTrac software for verification of image fusion, the positional reproducibility and accuracy of the ExacTrac Robotics, and intra-fractional patient motion (the accuracy of patient immobilization). "
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