Comparison of pencil-type ionization chamber calibration results and methods between dosimetry laboratories

Hourdakis, C. J.; Büermann, L; Ciraj-Bjelac, Olivera; Csete, I; Delis, Harry; Gomola, Igor; Persson, Linda; Novák, L.; Petkov, Ivailo; Toroi, Paula

doi:10.1016/j.ejmp.2015.09.008

Cited by 3 publications

(3 citation statements)

References 8 publications

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“…The slit-based calibration method was first proposed by the IAEA TRS 457 (IAEA 2007). Bochud et al proposed using the slit-based calibration method and later it was used by Merimaa et al and Hourdakis et al but the scatter correction in their studies was performed by extrapolating the ionization chamber current to a zero aperture width value (Bochud et al 2001, Merimaa et al 2012, Hourdakis et al 2016. This investigation reports a statistically significant variation of the scatter correction factor, K ap , as a function of aperture width.…”

Section: Discussionmentioning

confidence: 89%

“…Without such a correction, the variations in the N KL were found to be up to ∼15% for a diaphragm aperture ranging from 1 to 15 cm. In the work of Hourdakis et al a comparison between the slit-based air-kerma calibration method and the full-length irradiation method was performed using a Victoreen CT500-200 ionization chamber (Hourdakis et al 2016). The slit-based calibration method was recommended and a deviation from the nominal value of up to 2% for the active length of the chamber were reported.…”

Section: Introductionmentioning

confidence: 99%

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On the length used for CT ionization chambers to determine CTDI

DeWerd¹,

Khan²,

Jensen³

2022

Phys. Med. Biol.

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Objective: Computed Tomography Dose Index (CTDI) calculations based on measurements made with CT ionization chambers require characterization of two chamber properties: radiation sensitivity and effective length. The sensitivity of a CT ionization chamber is currently determined by calibration in an x-ray field that irradiates the entire chamber. Determination of the effective length is left to the user, and this value is frequently assumed to be equivalent to the nominal length—typically 100mm—stated by the manufacturer. This assumption undermines the intention and usefulness of CTDI calculation. Thus, a slit-based calibration, NKL, of the CT ionization chambers was proposed by collimating the x-ray beam to a well-defined aperture width. Approach: Four different CT ionization chambers (Exradin A101, Radcal 10x5-3CT, Victoreen 500-100, and Capintec PC-4P) are investigated in this work. Sensitivity profiles were measured for all four chambers and effective/rated chamber lengths were calculated. A novel Monte-Carlo based correction was proposed to account for the presence of the aperture. CTDI was calculated and compared for two calibration beams as well as for a commercial CT scanner using Exradin A101 and Radcal 10x5-3CT chambers. Main results: The nominal chamber length was found to deviate up to 21% compared to the effective length. Correction for the aperture depended on the aperture opening size. CTDI calculation results illustrate the potential 17% error in CTDI calculation that can be caused by assuming the effective chamber length is equivalent to the manufacturer’s stated nominal length. CTDI calculations with CT ionization chambers calibrated with an air-kerma length calibration method yield the smallest variation in the CTDI regardless of the chamber model. Significance: To avoid an erroneous CTDI, information regarding the chamber's effective length must be included in the calibration or stated by the manufacturer. Alternatively, a slit-based calibration can be performed.

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Section: Discussionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

On the length used for CT ionization chambers to determine CTDI

DeWerd¹,

Khan²,

Jensen³

2022

Phys. Med. Biol.

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“…Accordingly, transmission detectors have been developed to address these demands, and several commercial products are now available for clinical purposes (e.g., IQM (iRT Systems GmbH, Koblenz, Germany), OCTAVIUS III DAVID (PTW Freiburg GmbH, Freiburg, Germany), Delta4 Discover (ScandiDos AB, Uppsala, Sweden), and the Dolphin online monitoring system (IBA Dosimetry, Schwarzenbruck, Germany) [ 11 , 19 , 20 ].…”

Section: Introductionmentioning

confidence: 99%

Validation of new transmission detector transmission factors for online dosimetry: an experimental study

Park

Kim

et al. 2018

Radiat Oncol

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BackgroundThe demand for dose verification during treatment has risen with the increasing use of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in modern radiation therapy. This study aims to validate the transmission factors of a new transmission detector, the Dolphin online monitoring system (IBA Dosimetry, Schwarzenbruck, Germany), for clinical use.MethodsThe transmission factors of the Dolphin detector were evaluated using 6 MV, 6 flattening filter free (FFF), 10 MV, and 10 FFF clinical beams from a TrueBeam STx linear accelerator system. Two-dimensional (2D) dose distributions were measured through portal dosimetry with and without Dolphin to derive the transmission factors. The measurements were performed using 10 IMRT and 10 VMAT treatment plans. The transmission factors were calculated using a non-negative least squares problem solver for the 2D dose matrix. Normalized plans were generated using the derived transmission factors. Patient-specific quality assurance with normalized plans was performed using portal dosimetry and an ArcCheck detector to verify the transmission factors. The gamma passing rates were calculated for the 2%/2 mm and 1%/1 mm criteria.ResultsThe transmission factors for the 6 MV, 6 FFF, 10 MV, and 10 FFF beams, were 0.878, 0.824, 0.913, and 0.883, respectively. The average dose difference between the original plan without Dolphin and the normalized plan with Dolphin was less than 1.8% for all measurements. The mean passing rates of the gamma evaluation were 98.1 ± 2.1 and 82.9 ± 12.6 for the 2%/2 mm and 1%/1 mm criteria, respectively, for portal dosimetry of the original plan. In the case of the portal dosimetry of the normalized plan, the mean passing rates of the gamma evaluation were 97.2 ± 2.8 and 79.1 ± 14.8 for the 2%/2 mm and 1%/1 mm criteria, respectively.ConclusionsThe Dolphin detector can be used for online dosimetry when valid transmission factors are applied to the clinical plan.

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