الفهرس 
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Abstract
The aim of this work was to quantify the extent of set -up errors to conduct a quality assurance (QA) aspect of treatment delivery, verification of the treatment field’s position on different days using electronic portal fIlm and determination of the target absorbed dose delivered to the patient during the treatment session in the Radiotherapy Department, National Cancer Institute, Cairo University.
This study included a sample of twelve patients treated for malignant diseases of the pelvic region. For each patient, a number of Electronic port fIlms was taken twice weekly on the linear accelerator (6Mv). The total number of fIlms was 240fIlms, also the midline target absorbed dose measured using diode system.
Electronic port fIlm of set -up errors, were compared with simulator fIlm (Reference Image) by THERA VIEW anatomical matching software.
There are slight predominance errors in the (Y) direction with a systematic error (mean) 6.24 & 6.95 mm , followed by 4.43mm & 3.79mm in (X) direction AP and Lt portals field respectively . While the mean 2D-vector errors were 8.3, 8.7rnm in AlP and LT directions respectively The discrepancies in anterior posterior(AP) and lateral (L T) directions correlated to the number of film for each X and Y displacement are 65%, 76.66% and 54.16%,52.5% for:S 5 mm, while 25.83, 15.83% and 27.5%,23.33% for >5-10mm and 9.16%, 7.5% and 18,33,24.16% for >10mm respectively.
Also, the discrepancies in anterior posterior(AP) and lateral (L T) directions correlated to the number of film For 2D vector are 39.16% and 38.33% for :s 5 mm, 30% and 30.83% for >5-10mm and 30.83% and 30.83% for > 10 mm respectively.
The measurements of target midline absorbed dose ranged from 195 to 215 cGy with SD variation from 2.5 to 7.3%. The mean target absorbed dose were 205.91 cGy with SD variation 3.49 %.
The limits of the mean and standard deviation (SD) in the X direction might be comparable to other work while the limits of mean and SD in (Y) direction were exceeding that limits (SD :s 3) in AlP and L T Fields.
Increasing the accuracy of radiation dose delivery to the intended target should improve the tumor control probability TCP and reduce treatment-related morbidity This study clarified the importance of the immobilization methods with high quality fIxation in the reproducibility for the patient position during the treatment. Also the study has confIrmed the feasibility of fIeld setup verillcation with EPID for several times at the start of treatment course and afterwards on a regular interval (weekly); That may reflect the equal importance of portal imaging as a part of the routine quality assurance program in radiation therapy, with the stress on the electronic port fIlms ability of detection and measurement of set-up errors and eventually guidance of their correction.