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

Iwasaki A, Kimura S, Sutoh K, Kamimura K, Sasamori M, Seino M, Komai F, Takagi M, Terashima S, Hosokawa Y, Saitoh H, Miyazawa M
2017 Journal of Radiology and Imaging  
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
more » ... enter 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. 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 Research highlights Convolution methods are convenient for three-dimensional (3D) dose calculations, especially for an irregular-beam field with a non-uniform incident-beam intensity distribution. For a convolution method, we performed theoretical and experimental studies on 10-MV X-ray dose calculations in water phantoms with multileaf collimation (MLC) and/ or wedge filtration using a linear accelerator equipped with a pair of upper jaws, a pair of lower jaws, an MLC and a wedge filter. 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. We can conclude that the convolution method can achieve accurate dose calculations even under MLC and/ or wedge filtration.
doi:10.14312/2399-8172.2017-4 fatcat:lecccvcmcfcwjjey3mgbjkypdi