Quasi real time in vivo dosimetry for VMAT

Journal Article · Sun Jun 15 04:00:00 EDT 2014 · Medical Physics

DOI:https://doi.org/10.1118/1.4875685· OSTI ID:22250594

Fidanzio, A.; Azario, L. ^[1]; Porcelli, A. ^[2]; Greco, F. ^[2]; Cilla, S. ^[3]; Grusio, M. ^[1]; Balducci, M.; Valentini, V. ^[4]

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1. Istituto di Fisica, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)
2. U.O.C di Fisica Sanitaria, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)
3. 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)
4. U.O.C di Radioterapia, Università Cattolica del Sacro Cuore, Rome 00168 (Italy)

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 was 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.

• OSTI ID: 22250594
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 6 Vol. 41; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

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