title: Estimation of focal and extra-focal radiation profiles based on Gaussian modeling in medical linear accelerators.
abstract: The X-ray source or focal radiation is one of the factors that can degrade the conformal field edge in stereotactic body radiotherapy. For that reason, it is very important to estimate the total focal radiation profiles of linear accelerators, which consists of X-ray focal-spot radiation and extra-focal radiation profiles. Our purpose in this study was to propose an experimental method for estimating the focal-spot and extra-focal radiation profiles of linear accelerators based on triple Gaussian functions. We measured the total X-ray focal radiation profiles of the accelerators by moving a slit in conjunction with a photon field p-type silicon diode. The slit width was changed so that the extra-focal radiation could be optimally included in the total focal radiation. The total focal radiation profiles of an accelerator at 4-MV and 10-MV energies were approximated with a combination of triple Gaussian functions, which correspond to the focal-spot radiation, extra-focal radiation, and radiation transmitted through the slit assembly. As a result, the ratios of the Gaussian peak value of the extra-focal radiation to that of the focal spot for 4 and 10 MV were 0.077 and 0.159, respectively. The peak widths of the focal-spot and extra-focal radiation profiles were 0.57 and 25.0 mm for 4 MV, respectively, and 0.60 and 22.0 mm for 10 MV, respectively. We concluded that the proposed focal radiation profile model based on the triple Gaussian functions may be feasible for estimating the X-ray focal-spot and extra-focal radiation profiles.
authors: Department of Radiology, Kyushu University Hospital at Beppu, Tsurumihara Tsurumi, Beppu, Oita, Japan.
authors: Shigeo
authors: S
authors: Anai
authors: Hidetaka
authors: H
authors: Arimura
authors: Katsumasa
authors: K
authors: Nakamura
authors: Fujio
authors: F
authors: Araki
authors: Takaomi
authors: T
authors: Matsuki
authors: Hideki
authors: H
authors: Yoshikawa
authors: Satoshi
authors: S
authors: Yoshidome
authors: Yoshiyuki
authors: Y
authors: Shioyama
authors: Hiroshi
authors: H
authors: Honda
authors: Nobuo
authors: N
authors: Ikeda
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D016011:Normal Distribution; D010315:Particle Accelerators / Q000295:instrumentation*; D017785:Photons; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D014965:X-Rays