Résumé
Objective To study the spectrum structure of X-ray and simplify the description method of it. Methods By the general program of Monte Carlo Geant4 to study X-ray spectrum structure and angular distribution of X-ray energy spectrum. Results The results of percentage depth doses and profile curves at different depths of any radiation fields in water phantom calculated by Monte Carlo Geant4 were consistent with the measurements. Conclusions In radiotherapy, X-ray with same nominal energy have very similar dosimetry characteristics, this indicates they have very similar energy spectrum and angular distribution of spectrum. the differences of dosimetric details reflect the different details of the X-ray spectrum structure and angular distribution of X-ray energy spectrum. These studies have very important significances to rapidly build precise virtual source modeling for Monte Carlo calculation based on dose curves measurements in water phantom.
Résumé
ObjectiveTo analyze the effects of high-order scattered X-ray in dose calculation in radiotherapy,to resolve the problem of correcting the dose contribution of secondary and high-order scattering X-ray to the primary scattered X ray,and to provide a support for photon fast dose calculation method of Monte Carlo.MethodsBy the theory of cross-section in interaction between X-ray with material and Monte Carlo calculating results,to analysis the relative importance of primary scattered X-ray,secondary and high-order scattered of X-ray in dose calculation.ResultsThe contribution of secondary and high-order scattered X-ray to dose calculation was very small,it can be corrected to the primary scattered X-ray with a correction factor.ConclusionsThe results show that we can obtain a precise dose calculation for radiotherapy by only to tracking the contribution of primary X-rays and primary scattering X-ray,so,to establishing the database for primary scattering X-ray by Monte Carlo methods is important for fast dose calculation of Monte Carlo method.