الفهرس 
Treatment machines
CT in electron beam treatment planningOnly 14 pages are availabe for public view
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Abstract
Electron beam therapy is widely used in the management of cancers. The rapid dose fall-off and the short range of an electron beam enable the treatment of lesions close to the surface, while sparing the underlying tissues. In an extended source-tosurface (SSD) treatment with irregular field sizes defined by cerrobend cutouts, the underdosage of the lateral tissue may occur due to reduced beam flatness and uniformity. To study the changes in the beam characteristics, the depth dose, beam profile, and isodose distributions were measured at different SSDs for regular 10 Χ 10 cm 2 and 20 Χ 20 cm 2 cone, and for regular cutouts of field size 3 Χ 3 cm 2 and 20 Χ 20cm 2 for beam energies ranging from 6 to 20 MeV. The PDD (percentage depth dose), beam flatness, symmetry and uniformity index were compared. For lower energy (6 MeV), there was no change in the depth of maximum dose (R100) as SSD increased, but for higher energy (20 MeV), the R100 depth increased from 2 cm to 3 cm as SSD increased. This shows that as SSD increases, there is an increase in the depth of the maximum dose of higher energy beams. There is a +7 mm shift in the R100 depth when compared with regular and irregular field sizes. The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol(60580 ED3). There was a loss of beam flatness for irregular fields and it was more pronounced for lower energies as compared with higher energies, so that the clinically useful isodose level (80% and 90%) width decreases with increase in SSD. This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used. The dosimetry in the penumbra regions and central beam axis (CAX) of the beam profile depends on the dimensional characteristics of the Pb layer, such as its diameter and thickness. The aim of this study is to determine the dosimetric characteristics such as the beam profile, relative dose at the CAX and penumbra width at dm with varying diameters and different electron beam energies for different machine models.