الفهرس 
صفحة العنوانيوجد فقط 14 صفحة متاحة للعرض العام
 |  | from | 164 |  |  |
| | | from | 164 | | |
المستخلص
: During radiotherapy treatment, the patient commonly lies on a horizontal treatment table called a couch, also to ensure accurate positioning and repositioning of patients during their treatment used Immobilization devices. The material used for the couch top and Immobilization devices are chosen during the manufacturing process to minimize the effect of the couch and Immobilization devices on dose delivery, whoever they still have a dosimetric effect, where the couch top and Immobilization devices attenuate radiation beam increase skin dose and reduce tumor dose. In the modern radiotherapy technique approach of using multiple beam angles for dose delivery makes treatment planning in the presence of the couch and immobilization devices more challenging. However, their effects are not always considering in the dose calculation.
Aim: The aim of this work was to evaluate the amount of attenuation caused by carbon couch top and immobilization devices with different gantry angels of Arc modulated radiation delivery and to investigate the accuracy of Monaco treatment planning system on the dose calculation when the treatment fields pass through the couch top and the immobilization devices. Another aim was to determine the dosimetric clinical impact of the couch top and immobilization devices on the tumor, critical organs and skin with the VMAT pediatric patients.
Material and Methods: iBEAM evo IGRT Elekta couch top attenuation was measured with different field sizes and different gantry angles for 6 MV and 10 MV. The optimum electron density of the carbon fiber couch materials and the in-between foam were optimized and modelled into Monaco TPS. Moreover, the dosimetric effect of the carbon fiber couch was demonstrated in a phantom study. In the clinical part, ten paediatric craniospinal (medulloblastoma) patients were involved in this study. All patients were immobilized using a head and neck fixation equipment and VMAT plans were created for each patient with and without considering the carbon fiber couch top in dose calculation. Comparisons of the dosimetric parameters were carried out using dose volume histogram for 6 MV and 10 MV beam energy. In addition, the immobilization devices of head and neck cases were delineated and considered in the dose calculation.
Results:The results showed that the highest attenuation values were recorded 4.6% at gantry angle 230◦ for the smallest field size (3x3 cm2) for 6 MV which has the longest track path through the couch directed to the isocentre of the phantom. And it was found that the best fitting values of the electron densites were 0.3 g/cm3 for carbon fiber and 0.03 g/cm3 for foam, these values provided the best agreement between Monaco TPS calculated dose and measured dose. It was observed that the percentage of couch or extension changes the dose distribution , specifically affecting the surface dos and build up region, which was found that the increase in the surface dose for 6 MV by a percentage 86% and 61.7% for 3 x 3 cm2 ,15 x 15 cm2 field size respectively when using extension 415. It was noticed that the extension 650 has more sever dosimetric effect on the surface dose and build up region dose. In Medulloblastoma plans ; it was observed that the most effect of insertion the couch top in the dose calculation was found in the skin dose which increased by value of 20% for 6 MV and 20.6% for 10 MV. from the immobilization devices results it was found that the effect of the immobilization devices on the PTV95% at 6 MV beam energy reduced by 3.49%. Meanwhile, the skin doseD1% increased by 15%, also the mean skin does was increased by 57% with presence the immobilization devices.
Conclusion:
Modelling of the IGRT carbon fiber couch top in Monaco TPS must be performed institutionally to fine the fitted optimum density values of the two carbon fiber couch layers and the in-between foam. The precise twiking of the carbon fiber couch in to the Monaco TPS leads to safe radiation dose delivery to the cancer patients. In addition all the immobilization devices must be delineated and considered