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EN
Background: Normalized glandular dose (DgN) is an important dosimetric quantity in mammography. Aim: In this study, the effect of the presence of breast cysts and their size, number and location on DgN is evaluated. Materials and methods: The effect of the presence of cysts in breast was examined using MCNPX code. This was performed by taking homogeneous breast phantoms containing spheroid breast cysts into account. The radius of the cysts, numbers of the cysts, and depth of the cysts, and their location were variable. Various electron energies were also considered. Finally, these results were compared with the results of a cyst-less breast phantom. Results: The results show that the effect of the presence of cysts in the breast depends on the size, number and location of cysts. The presence of cysts at lower depths leads to a decrease in the DgN values, compared to the breast phantom without cysts. The presence of cysts in the breast phantom has an effect of -7 to +14 percent on the DgN values under the conditions considered in this modeling. This effect is independent of the X-ray tube voltage, the breast phantom thickness, and glandular ratio, and depends only on the number and size and location of the cysts. The bigger radius and number of cysts, the greater effect on DgN value.
EN
Objective: The main purpose of this study is to calculate the effective source to surface distance (SSDeff) of small and large electron fields in 10, 15, and 18 MeV energies, and to investigate the effect of SSD on the cutout factor for electron beams a linear accelerator. The accuracy of different dosimeters is also evaluated. Materials and methods: In the current study, Elekta Precise linear accelerator was used in electron beam energies of 10, 15, and 18 MeV. The measurements were performed in a PTW water phantom (model MP3-M). A Semiflex and Advanced Markus ionization chambers and a Diode E detector were used for dosimetry. SSDeff in 100, 105, 110, 115, and 120 cm SSDs for 1.5 × 1.5 cm2 to 5 × 5 cm2 (small fields) and 6 × 6 cm2 to 20 × 20 cm2 (large fields) field sizes were obtained. The cutout factor was measured for the small fields. Results: SSDeff in small fields is highly dependent on energy and field size and increases with increasing electron beam energy and field size. For large electron fields, with some exceptions for the 20 × 20 cm2 field, this quantity also increases with energy. The SSDeff was increased with increasing beam energy and field size for all three detectors. Conclusion: The SSDeff varies significantly for different field sizes or cutouts. It is recommended that SSDeff be determined for each electron beam size or cutout. Selecting an appropriate dosimetry system can have an effect in determining cutout factor.
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