الفهرس 
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Abstract
Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor in adults that has been around 70% of high-grade gliomas.
Radiation therapy is one of the bases for (GBM) standard treatment. The three-dimensional conformal radiotherapy (3DCRT) is considered to be the most common technique to treat GBM, but Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are becoming widely used to compete it.
The aim of the present work is to compare the effect of patient setup error on the delivered dose by different techniques and hence defined the most accurate technique to deliver the prescribed dose to the target.
A set of 9 GBM patients are selected with target prescribed dose 60 Gy and very close to organs at risk (OARs). The accepted plans by different techniques were recalculated after applying a simulation setup error by shifting the plan isocenter 3mm, 5mm and 7mm. Analysis of target evaluation parameters of all accepted plans (27 origin plans) and new simulation setup error plans (81 plans) was done to compare the effect of patient setup error.
This study showed that VMAT and IMRT without setup error are comparable in planning target volume (PTV) coverage and OAR sparing, however VMAT is more preferable due to better target coverage, easy delivery of treatment and timeless on the machine, while 3DCRT is the least one of the three techniques in the coverage of the PTV by 57Gy (95% of the prescribed dose).
The setup error effect on delivered dose to the PTV appeared clearly in the target evaluation parameters [homogeneity index (HI), conformity index (CI) and conformity number (CN)]. The measurements of the setup error effect on the PTV for shifting isocenter till 7mm between 3DCRT, IMRT and VMAT showed that they have an average percentage error for HI (1.9%, 22.2%, and 16.5%), for CI (2.6%, 11%, and 15.3%), while for CN (3.7%, 41.6%, and 39%) respectively. Then target evaluation parameters are more sensitive to patient setup error in VMAT and IMRT techniques, while this effect decreases with 3DCRT technique.
On the other hand the present study showed that the setup errors effect are nearly equals to the OARs for the used techniques except the small volumes organs which are very sensitive to patient setup errors as (lens and cochlea) even that small setup error.
The comparison of the 3mm setup error effect between 3DCRT, IMRT and VMAT shows that an average percentage error for right lens (8%, 44%, and 25%), for left lens (9%, 33%, and 24%), while for ipsilateral cochlea (0.5%, 4%, and 7%) respectively. Also in 5mm setup error for right lens (14%, 71%, and 45%), for left lens (16%, 64%, and 52%), while for ipsilateral cochlea (0.7%, 8.6%, and 14%) respectively. Finally in 7mm setup error for right lens (24%, 92%, and 66%), for left lens (26%, 82%, and 86%), while for ipsilateral cochlea (0.9%, 12%, and 20%) respectively.
So since IMRT and VMAT are more complex techniques than 3DCRT then they need more accurate verification for target position by using advanced imaging techniques to avoid any setup errors. The decision of plan selection should not depend only on DVH especially when two competitor techniques that similar in PTV coverage and OAR sparing.