Reconsideration of the Iwasaki–Waggener iterative perturbation method for reconstructing high-energy X-ray spectra

Iwasaki, Akira; Kimura, Shigenobu; Sutoh, Kohji; Kamimura, Kazuo; Sasamori, Makoto; Seino, Morio; Komai, Fumio; Terashima, Shingo; Kubota, Mamoru; Narita, Yuichiro; Hosokawa, Yoichiro; Miyazawa, Masaaki

doi:10.1007/s12194-012-0160-7

Cited by 1 publication

(5 citation statements)

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“…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%

“…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). When applying the density scaling theorem [9][10][11] to the in-water primary and scatter dose kernels again under the conditions that the phantom, wedge filter, wedge holder and MLC are treated as parts of a unified irradiated body, the use of the relative electron density (ρ e ) is not feasible.…”

Section: Dose Calculation Principlementioning

confidence: 99%

“…with , where OCR source (R 0 ) is the source offcenter ratio [6], obtained by assuming that it is a function of only for an open infinite A jaw field (defined as the in-air beam intensity (in water collision kerma) at a point that is R 0 distant from the isocenter to that at the isocenter (that is, OCR source (0) = 1), where the OCR source dataset was produced by applying an in-air chamber response function [4] of y(R 0 ) = exp(0.002R 0 -0.00002R 0 2 ) to an in-air dose dataset measured only at points of Y beam ≥ 0 on the Y beam axis). RRF jaw is the jaw-collimator radiation reflection factor [6], letting RRF jaw =1 and RRF jaw >1, respectively, inside and outside the A jaw field.…”

Section: In-air Output Factor Calculation For Open Mlc Fieldsmentioning

confidence: 99%

“…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%

“…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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Section: Dose Calculation Principlementioning

confidence: 99%