جستجوی مقالات مرتبط با کلیدواژه "4 gaussian function" در نشریات گروه "پزشکی"

Recently, electron beams are widely used for superficial and skin lesions treatment. Since the accelerator devices, create electron beams with finite energies, the treatment area is limited to a specified depth. The objective of this study was to assess the effect of combination of electron beams with different energies and different contribution in order to produce PDD curve with a more uniform central dose distribution for the shallow superficial lesions treatment (up to cm 3). The results were compared with using a single electron beam energy. Subjects and at First, percentage depth dose (PDD) was measured by using a Varian accelerator devices for energies 4, 6, 9, 12 Mev of electron beams and field size 20 × 20 cm2. Then, PDD curve was converted to dose curve. 4 Gaussian function was fit to dose curve using MATLAB software and the best combination was selected by combining different proportions of each of this functions. percentage of the build up dose increased to about %90-%95 maximum dose and also percentage of the surface dose increases to about %90 maximum dose by combination of electron beams with different energies and different contribution. low energy electron beams Combination cause optimization of the dose distribution PDD curve. Furthermore, we can produce electron beam with arbitrary energy by this method.

Background and Electron beams are extensively used in superficial cancer therapy. Unlike photon therapy, percentage depth dose curves (PDD) do not specify a maximum point in high energy electron therapy and include a depth range. The aim of this study was to obtain PDD by an analytical formulation which can be helpful to acquire the size of treatment area and other treatment factors such as the depth of maximum dose, the most probable energy (Ep), practical range (Rp), and the depth which the dose reaches the peak of 50% (R50). Measurements of PDD was done in radiotherapy department of Ahvaz Golestan Hospital for Siemens Primus Plus accelerator, using ionization chamber CC13 dosimeter and a water phantom for energies of 6, 9, 12, 15, 18, and 21 MeV and different field sizes at various depths. Data was analyzed using MATLAB 7.8 software. The function which had the best fit to the data was selected. This function was used to calculate the, Rp and R50 points for each field size and energy. The dependence of these points to field size and energy were also obtained. We found that 4 Gaussian function had the best fit to the data (). Rapid dose reduction was observed after a relatively flat area. The curve had a sequence that was due to photon contamination. R50and Rp points obtained for the various fields and energies by analytical function revealed that R50 depends on the field size and energy. But, Rp depends only on energy and does not depend on field size variation.