The 6MV photon beam production by the Elekta Line accelerateur of Tripoli of medical center (TMC) was modeled using Beamnrc and Dosexyzne Monte Carlo codes. The Beamnrc code was used to model the accelerator head and generate phase files. The phase space files were then used as input to the Dosexyzne code to simulate octogenarian deth dose and beam profiles. simulation were first stared using nominal provided by the vendor, a field size of 10x10cm2 and Source to surface distance (SSD) of 100 cm. simulation were compared with experimental data and energy tuning procedures were applied to validate the model. Energy tuning procedures indicated that the nominal energy of 6 MV and a FWHM of the Gaussian distribution of the source of 0.35 cm were the optimal energy and FWHM for the model. The depth of maximum dose at 6 MV was found to be 1.5 cm. The percentage relative differences between calculated and experimental Pdd(s) ranged from 0.5% to 3% for field size of 10cm2 and reached a value of 8% at depths greater than 20cm, The model was later used to calculate PDD(s) and beam profile and output factors for different field size ranging from 3x3cm2 to 25x25cm2. Calculated output factors were in good agreement with experimental values (the percentage relative differences ranged from 1% to 4%). (Author) arabic 42 English 152
Karima Elmasri, Tawfik Giaddui(12-2012)

Dual-energy x-ray absorptiometry (DXA) is an established modality for the assessment of bone mineral density. DXA has also been used for the detection of abdominal aortic calcification (AAC) using lateral images taken for vertebral fracture assessment (VFA). In this phantom study, the capability of VFA for the detection of AAC was investigated. A Perspex phantom of variable width in the range 15-30 cm was used to simulate abdominal soft tissue. Aluminium strips of thickness 0.05-2.0 mm were sandwiched between two halves of the phantom to mimic aortic calcification. VFA images of the phantom were acquired in single-energy mode and analysed by placing regions of interest over the aluminium strip and an adjacent area of Perspex. For each phantom width, the minimum detectable aluminium thickness was assessed visually and related to contrast-to-noise ratio (CNR). Linearity of pixel value with aluminium thickness was tested by linear regression and correlation. Repeatability was measured with five repeated scans for selected phantom configurations. The minimum thickness of aluminium that could be visualised increased with phantom width and varied from 0.05 mm at 15 cm Perspex to 0.5 mm at 30 cm Perspex; the CNR threshold was about 0.03. At all phantom widths, the variation of pixel value with aluminium thickness was strongly linear (r²>0.98, p
Karima Elmasri, William David Evans, Yulia Hicks(6-2017)

Abstract: A 6MV and 15MV electron beams produced by the Elekta precise SL-25 linear accelerator at the Tripoli Medical Center (TMC) were modeled using the MCNP-4C code. Firstly the photon beam energies are tuned by comparison to experimental results previously performed at the TMC. Only the beam energy of the 6MV is modified to 6.2MV. Secondly the percent depth dose curves and beam profiles are calculated for the two energies in different field sizes in the water phantom. Matching with experiment is within an acceptable published allowance of 2%. The distances at which the maximum depth dose in the water phantom is reached are calculated as (1.5cm -1.7cm) for the 6.2MV setting and (2.7cm-3cm) for the 15MVsetting.
خديجة عمر بن ابراهيم (2011)