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Article Dans Une Revue Medical Physics Année : 2016

Accuracy of a dose-area product compared to an absorbed dose to water at a point in a 2 cm diameter field

Résumé

Purpose: Graphite calorimeters with a core diameter larger than the beam can be used to establish dosimetric references in small fields. The dose-area product (DAP) measured can theoretically be linked to an absorbed dose at a point by the determination of a profile correction. This study aims at comparing the DAP-based protocol to the usual absorbed dose at a point protocol in a 2 cm diameter field for which both references exist. Methods: Two calorimeters were used, respectively, with a sensitive volume of 0.6 cm (for the absorbed dose at a point measurement) and 3 cm diameter (for the DAP measurement). Profile correction was calculated from a 2D dose mapping using three detectors: a PinPoint chamber, a synthetic diamond, and EBT3 films. A specific protocol to read EBT3 films was implemented and the dose-rate and energy dependences were studied to assure a precise measurement, especially in the penumbra and out-of-field regions. Results: EBT3 films were found independent on dose rates over the range studied but showed a strong under-response (18%) at low energies. Depending on the dosimeter used for calculating the profile correction, a deviation of 0.8% (PinPoint chamber), 0.9% (diamond), or 1.9% (EBT3 films) was observed between the calibration coefficient derived from DAP measurements and the one directly established in terms of absorbed dose to water at a point. Conclusions: The DAP method can currently be linked to the classical dosimetric reference system based in an absorbed dose at a point only with a confidence interval of 95% (k = 2). None of the detectors studied can be used to determine an absorbed dose to water at a point from a DAP measurement with an uncertainty smaller than 1.2%. (C) 2016 American Association of Physicists Medicine.
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Dates et versions

hal-01867955 , version 1 (03-10-2023)

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Stéphane Dufreneix, Aimé Ostrowsky, Benjamin Rapp, Josiane Daures, jean-marc bordy. Accuracy of a dose-area product compared to an absorbed dose to water at a point in a 2 cm diameter field. Medical Physics, 2016, 43 (7), pp.4085 - 4092. ⟨10.1118/1.4953207⟩. ⟨hal-01867955⟩
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