Characteristic features of a high‐energy x‐ray spectra estimation method based on the Waggener iterative perturbation principle

Iwasaki, Akira; Kubota, Mamoru; Hirota, Junichi; Fujimori, Akira; Suzaki, Katsumasa; Aoki, Masahiko; Abe, Yoshinao

doi:10.1118/1.2359227

Cited by 11 publications

(14 citation statements)

References 14 publications

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“…This method is relatively simple and has been implemented in a large range of x-ray energies. [14][15][16][17][18] Transmission methods usually consist of two steps: ͑1͒ Measuring the transmission data for different thicknesses of materials and ͑2͒ reconstructing the spectra by solving the linear equations that represent the attenuation processes of x-ray photons. In this study, an expectation maximization ͑EM͒ method was used to solve the equations.…”

Section: Introductionmentioning

confidence: 99%

CT scanner x‐ray spectrum estimation from transmission measurements

Duan¹,

Wang²,

Yu³

et al. 2011

Medical Physics

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Purpose:In diagnostic CT imaging, multiple important applications depend on the knowledge of the x-ray spectrum, including Monte Carlo dose calculations and dual-energy material decomposition analysis. Due to the high photon flux involved, it is difficult to directly measure spectra from the x-ray tube of a CT scanner. One potential method for indirect measurement involves estimating the spectrum from transmission measurements. The expectation maximization ͑EM͒ method is an accurate and robust method to solve this problem. In this article, this method was evaluated in a commercial CT scanner. Methods: Two step-wedges ͑polycarbonate and aluminum͒ were used to produce different attenuation levels. Transmission measurements were performed on the scanner and the measured data from the scanner were exported to an external computer to calculate the spectra. The EM method was applied to solve the equations that represent the attenuation processes of polychromatic x-ray photons. Estimated spectra were compared to the spectra simulated using a software provided by the manufacturer of the scanner. To test the accuracy of the spectra, a verification experiment was performed using a phantom containing different depths of water. The measured transmission data were compared to the transmission values calculated using the estimated spectra. Results: Spectra of 80, 100, 120, and 140 kVp from a dual-source CT scanner were estimated. The estimated and simulated spectra were well matched. The differences of mean energies were less than 1 keV. In the verification experiment, the measured and calculated transmission values were in excellent agreement. Conclusions: Spectrum estimation using transmission data and the EM method is a quantitatively accurate and robust technique to estimate the spectrum of a CT system. This method could benefit studies relying on accurate knowledge of the x-ray spectra from CT scanner.

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Section: Introductionmentioning

confidence: 99%

CT scanner x‐ray spectrum estimation from transmission measurements

Duan¹,

Wang²,

Yu³

et al. 2011

Medical Physics

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“…We reconstructed [3,4] a new set of energy fluence spectra for the accelerator as follows. We measured sets of in-air transmission data at points on the Y beam axis where Y beam ≥ 0 using an ionization chamber with an acrylic buildup cap (a factor of f cap = 0.25 was assumed [4] to account for radiation attenuation and scatter in the buildup cap), in which we used acrylic attenuators of 0-30 cm in thickness and lead attenuators of 0-3 cm in thickness at off-axis distances of R 0 = 0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.5, 17.5 and 19.5 cm.…”

Section: Spectra and Dose Kernelsmentioning

confidence: 99%

“…are expressed in Gy; the beam water collision kerma (or the primary water collision kerma) components ( and ) are expressed in Gy; the dose kernels (H 1,2 , K 1,2 , h phan , h wedge , h MLC , k phan , k wedge , k MLC , etc.) are expressed in cm -3 ; the volume element (∆V) is expressed in cm 3 ; and the area element (∆S) is expressed in cm 2 .…”

Section: Symbols and Unitsmentioning

confidence: 99%

“…The dose calculation was performed using a convolution method that utilizes special types of in-water primary and scatter dose kernels (H 1,2 and K 1,2 (see Appendix A)), formed for the energy bins of X-ray spectra [3,4] reconstructed as a function of the off-axis distance. It should be noted that the usual number of energy bins is approximately ten, and that the reconstructed X-ray spectra can reasonably be applied [4] to media with a wide range of effective Z numbers (e.g., from water to lead).…”

Section: Dose Calculation Principlementioning

confidence: 99%

“…The present paper deals with a kind of collapsed cone convolution; however, it is to be emphasized that the dose calculation is performed using multiple primary-and scatter-dose kernels that are formed with the use of X-ray spectra reconstructed [3,4] as a function of the off-axis distance.…”

Section: Introductionmentioning

confidence: 99%

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10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

Iwasaki¹,

Kimura²,

Sutoh³

et al. 2017

J Radiol Imaging.

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Purposes: This paper highlights a 10-MV X-ray convolution dose calculation method in water using primary and scatter dose kernels formed for energy bins of X-ray spectra reconstructed as a function of the off-axis distance for a linear accelerator equipped with pairs of upper and lower jaws, a multileaf collimator (MLC) and a wedge filter. Methods: The reconstructed X-ray spectra set was composed of 11 energy bins. To estimate the in-air beam intensities at points on the isocenter plane for an MLC field, we employed an MLC leaf-field output subtraction method, using an extended radiation source on each of the X-ray target and the flattening filter as well as simplified twodimensional plates to simulate the three-dimensional jaws and MLC structures. A special correction factor was introduced for nonuniform incident beam intensities, particularly produced at MLC fields. The in-phantom dose calculation was performed by treating the phantom, the wedge filter, the wedge holder and the MLC as parts of a unified irradiated body, where we proposed to use a special factor for the density scaling theorem within the unified irradiated body. Conclusions: The phantom dose was generally separated into nine dosecomponents: the primary and scatter dose-components produced in the phantom; the primary and scatter dose-components emanating from the wedge, the wedge holder and the MLC; and the electron contamination dose-component. From the calculated and measured percentage depth dose (PDD) and off-center ratio (OCR) datasets, we may conclude that the convolution method can achieve accurate dose calculations even under MLC and/or wedge filtration.Keywords: convolution method; X-ray spectra; dose kernels; wedge; multileaf collimation; MLC leaf-field output subtraction Citation: Iwasaki A, Kimura S, Sutoh K, Kamimura K, Sasamori M, Seino M, Komai F, Takagi M, Terashima S, Hosokawa Y, Saitoh H, Miyazawa M. 10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance. J

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Determination of radiotherapy X-ray spectra using a screen-film system

Garnica-Garza

2008

Med Biol Eng Comput

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A method to determine the X-ray spectrum delivered by a medical linear accelerator is presented. This method consists of an analytical calculation of the primary spectrum using the Schiff bremsstrahlung cross-section formula. A correction factor that accounts for the scatter component of the spectrum is estimated by comparing the signal in two screen-film systems to a theoretical prediction using a model of energy deposition in such detectors. The model makes use of the quantum absorption efficiency and the average energy deposited per interacting photon concepts. These two quantities are calculated by means of Monte Carlo simulations of the screen-film systems used. This method is capable of determining the spectrum as a function of the spatial position across a plane perpendicular to the beam central axis. It does not, however, render information about the direction cosines of the X-ray fluence crossing such a plane, a requirement in order to produce a full phase-space file that can be used in conjunction with a Monte Carlo dose calculation engine.

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Characteristic features of a high‐energy x‐ray spectra estimation method based on the Waggener iterative perturbation principle

Cited by 11 publications

References 14 publications

CT scanner x‐ray spectrum estimation from transmission measurements

CT scanner x‐ray spectrum estimation from transmission measurements

10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

Determination of radiotherapy X-ray spectra using a screen-film system

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