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SU‐FF‐T‐354: Penumbra Measurement with the Use of a 2D Pixel Ionization Chamber
Author(s) -
Peroni C,
Brusasco C,
Cirio R,
Donetti M,
Giordanengo S,
Gomola I,
Iliescu S,
Marchetto F,
Nastasi U,
Stasi M
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2241275
Subject(s) - penumbra , ionization chamber , multileaf collimator , pixel , ionization , dot pitch , detector , optics , physics , dosimetry , materials science , nuclear medicine , linear particle accelerator , beam (structure) , medicine , ion , ischemia , quantum mechanics , cardiology
Purpose: To attest the accuracy of the penumbra measurement with the use of a 2D pixel ionization chamber. Method and Materials: Penumbra measurements were carried out for several clinical cases, treated with Intensity Modulated Radiation Therapy, with a pixel ionization chamber and with radiographic film as reference. The pixel chamber consists of a matrix 1020 detectors, each 4.5 mm diameter and 5 mm height at a pitch of 7.62 mm. Each of the 1020 ionization chambers was read out independently with no dead time. Standard radiographic films have been used, scanned with a pitch of 0.16 mm and 0.40 mm. Both detectors were irradiated with 6 MV photon beams, using a linac equipped with a 120‐leaves multileaf collimator. Measured dose profiles were fitted with a “Fermi‐like” function: f ( x ) = 11 + ea ( x − x 0 )with x 0 and a as free parameters; the value for the penumbra could then be derived from the fit. The two sets of data were compared. Results: The data for the penumbra measured with the pixel chamber and the film for several IMRT fields show a strong linear correlation. This made it possible to correct the penumbra values obtained with the pixel ionization chamber to obtain a precise measurement even in a range well below the pixel dimensions. Conclusion: The 2D pixel ionization chamber has been shown to be able to measure the penumbra down to ∼ 2mm with an accuracy of ± 0.6 mm. This device can then efficiently replace radiographic film in some QA procedures with a significative gain in time as it gives results in real‐time and data are immediately available. Conflict of Interest: Research sponsored by MAESTRO, European project on Methods and Advanced Equipment for Simulation and Treatment in Radiation Oncology.