الفهرس 
Introduction & Aim of the workOnly 14 pages are availabe for public view
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Abstract
The dosimetric measurements of nonstandard fields used in radiotherapy, with high dose gradients involved are hard duty. These measurements are very important for quality assurance and radiotherapy regulations. The complexity of new radiotherapy techniques led to the necessity of treatment dosimetric verification in the hospital quality assurance programs. This verification is used to check that the dose distributions delivered by the radiotherapy machine match the corresponding planned dose distributions obtained from treatment planning systems, and within the required tolerances. The aim of this study is to determine the accuracy of several radiotherapy treatment planning systems (TPSs) for dose calculation in a homogenous phantom, and potential limitations of the dose calculation algorithm. The measurements of this study were made at Mansoura university hospital, Radiotherapy and Nuclear Medicine department and Alexandria Clinical Oncology Center “Ayadi-Almostakbal”. The measurements in this study was carried out by using Elekta precise linear accelerator with 80 multileaf collimator (MLC) leaf and Siemens Artiste linear accelerator with 160 leaf, PTW dosimetry system, slabs solid phantom, radiographic film. The measured data compared with data from Elekta precise TPS, Xio TPS, and Prowess TPS, the comparison made by PTW-Verisoft. The measurement of this study involves quality control of MLC, to ensure that the MLC shapes are correctly aligned to the patient. This part was made by using radiographic films and solid slabs phantom. The second part of measurements involves the measurements of nonstandard, complex fields, such as small symmetric fields, asymmetric fields, wedged asymmetric fields and fields with oblique incidence angle. This part was measured by using water phantom with semiflex ionization chamber connected to PTW UNIDOSE dosimeter. Recommendations for manufactures: The results obtained from the QA of Elekta MLC, recommended that the multileaf width should be decreased to decrease the stepping edge of radiation field, which leads to the protection of the healthy organs surrounding the treated site. Recommendations for physicists: We have made a set of measurements to verify photon dose calculations. This set includes measurements of small fields, asymmetric open fields, asymmetric wedged fields, oblique incidence fields in water phantom. This data set was designed so that it could be used for general verification of photon dose calculation algorithms to avoid the under or over dose estimation to the treated site.