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Title: Quasi real time in vivo dosimetry for VMAT

Purpose: Results about the feasibility of a method for quasi real timein vivo dosimetry (IVD) at the isocenter point for volumetric modulated arc therapy (VMAT) are here reported. The method is based on correlations between the EPID signal and the dose on the beam central axis. Moreover, the γ-analysis of EPID images was adopted to verify off-axis reproducibility of fractionated plan delivery. Methods: An algorithm to reconstructin vivo the isocenter dose, D{sub iso}, for RapidArc treatments has been developed. 20 VMAT plans, optimized with two opposite arcs, for prostate, pancreas, and head treatments have been delivered by a Varian linac both to a conic PMMA phantom with elliptical section and to patients. The ratios R between reconstructed D{sub iso} and the planned doses were determined for phantom and patient irradiations adopting an acceptance criterion of ±5%. In total, 40 phantom checks and 400 patient checks were analyzed. Moreover, 3% and 3 mm criteria were adopted for portal image γ-analysis to assess patient irradiation reproducibility. Results: The average ratio R, between reconstructed and planned doses for the PMMA phantom irradiations was equal to 1.007 ± 0.024. When the IVD method was applied to the 20 patients, the average R ratio wasmore » equal to 1.003 ± 0.017 and 96% of the tests were within the acceptance criteria. The portal image γ-analysis supplied 88% of the tests within the pass rates γ{sub mean} ≤ 0.4 and P{sub γ<1} ≥ 98%. All the warnings were understood comparing the CT and the cone beam CT images and in one case a patient's setup error was detected and corrected for the successive fractions. Conclusions: This preliminary experience suggests that the method is able to detect dosimetric errors in quasi real time at the end of the therapy session. The authors intend to extend this procedure to other pathologies with the integration of in-room imaging verification by cone beam CT.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [3] ;  [5] ;  [1] ; ;  [6] ;  [1] ;  [2] ;  [7]
  1. Istituto di Fisica, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)
  2. (Italy)
  3. (INFN), Sezione di Roma Tre, Rome 00146 (Italy)
  4. U.O.C di Fisica Sanitaria, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)
  5. U.O di Fisica Sanitaria, Fondazione di Ricerca e Cura Giovanni Paolo II, Campobasso 86100, Italy and Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma Tre, Rome 00146 (Italy)
  6. U.O.C di Radioterapia, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)
  7. (INFN), Sezione di Roma Tre, Rome 00168 (Italy)
Publication Date:
OSTI Identifier:
22250594
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ALGORITHMS; AMINO ACIDS; COMPUTERIZED TOMOGRAPHY; DOSIMETRY; IMAGE PROCESSING; IMAGES; IN VIVO; IRRADIATION; LINEAR ACCELERATORS; PANCREAS; PATHOLOGY; PATIENTS; PHANTOMS; PMMA; PROSTATE; RADIATION DOSES; RADIOTHERAPY