الفهرس 
CHAPTER I Basics of radiotherapyOnly 14 pages are availabe for public view
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Abstract
Radiation therapy (RT) plays currently significant role in curative treatments of several cancers. Tumor eradication and normal tissue complications correlate to dose absorbed in tissues. This dependence is steep and crucial that actual dose within patient accurately correspond to the planned dose. All factors in a RT procedure contain uncertainties which require strict quality assurance.
During treatment, the most important errors are set-up error and organ motion leading to day-to-day variations. Many ways are used to define the margins required for these errors. In this study, an overview of errors is given in radiotherapy and margin recipes, based on physical and biological considerations. Bladder and Rectum motions are treated separately.
The systematic error is usually described and calculated in forms of a patient population and is considered to be composed of errors of target motion, setup, delineation and transfer and summarized according to the following Equation
Σ2=Σ 2 motion +Σ2 set up +Σ2 delineation +Σ2 transfer
The random error is defined according to the following Equation
σ 2 = σ 2motion + σ 2set-up
For patients who received RT for a Pelvis cancer, a Linear Accelerator (LA) equipped with a camera-based EPID was considered for inclusion in the study. All patients receiving RT with anterior-lateral portals and with at least 8 sets of portal images were included in the data set. A total of 20 patients with bladder cancer treated 3DCRT have met the inclusion criteria
XIV
on which 186 images and 558-point positions were available for analysis. By using the acquired images the magnitude of the systematic and random error were determined in the vertical, longitudinal and lateral direction. One or two portal weekly before the treatment fraction, anterior and lateral portal image was acquired and compared to the DRRs using amorphous silicon (a-Si), automatic and manual matching were applied. Couch translation only was used to account for marker position displacements, followed by a second lateral portal image to verify isocenter position.
This work includes a total of 186 portal images during treatment of 20 patients. Set-up displacement was found with a variation of 0.2 to 0.65 cm (max).The random errors for vertical, longitudinal and lateral were (2.53), (3.57) and (2.61) mm, respectively. and the systematic errors for vertical, longitudinal and lateral were (2.81), (3.37) and (2.85) mm respectively. And the calculated PTV margins were to be 8.85, 8.92 and 11.82 mm for vertical, lateral and longitudinal respectively.
Overall results of this study, revealed the idea that the action level should not exceed more than 3 mm in any direction.