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A Transmission Detector Based On Ion Chambers as a Constancy Tool for the Quality Assurance of a Medical Accelerator

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A Giuliacci

A Giuliacci1*, S Ondrej2 , M David3 , S Engelhardt4 , R Ringler5 , (1) ,,,(2) IBA Dosimetry GmbH, Schwarzenbruck, Bayern, (3) IBA Dosimetry GmbH, Schwarzenbruck, Bayern, (4) Ostbayerische Technische Hochschule Amberg-Weiden, Amberg, Bayern, (5) Ostbayerische Technische Hochschule Amberg-Weiden, Amberg, Bayern


SU-I-GPD-T-464 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To validate a transmission detector as a tool to verify the constancy of photon beams dosimetric parameters during daily and monthly quality assurance (QA) of a linear accelerator.

Methods: A 2D transmission detector, attached at LINAC’s head (SDD=61cm), is compared to a reference detector at isocenter in a plastic phantom. The transmission detector is based on a 2D array of parallel-plate ion chambers with 5mm sensor pitch (at detector plane) and 2mm electrode distance.Measurements have been performed according to AAPM Task Group 142 report and DIN 6847-5 standard.A Farmer chamber is used as a reference to determine repeatability, reproducibility, dose linearity (in the range 2-500MU), dose rate linearity (in the range 50-1000MU/min) and dose resolution (about 100MU).A commercial 2D array of ion chamber is used as a reference to determine stability over three months of beam profiles and output measurements.Flattened and unflattened beam qualities (in the range 6-15MV) and field sizes from 5x5cm² to 40x40cm² (at isocenter) have been used

Results: Dose linearity, dose rate linearity and resolution of the transmission detector are better than 1%.Repeatability and reproducibility are better than 0.5%. Stability of output, symmetry and flatness of profiles are better than 0.5%.Stability of field size and penumbra width measurements is better than 1mm. Results are independent from the beam quality.

Conclusion: The dosimetric performances of the transmission detector make it suitable for constancy checks of all photons-related dosimetric parameters in daily and monthly LINAC QA. Its use may increase efficiency and accuracy of QA, since it is quickly setup in a position fixed with respect to the LINAC’s head.

Funding Support, Disclosures, and Conflict of Interest: Some of the authors (A.Giuliacci, O.Sevela, D.Menichelli) are employees of IBA Dosimetry GmbH. This work is completely founded by IBA Dosimetry GmbH

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