Depth dose characteristics of electron beams at extended SSDS

The purpec: of this study is to investigate the behaviour of the percent depth dose curves (%DD) and surface doses of electronbeams at extended Source-to Surface Distances (SSDS). A (GE) Saturne 42 linear accelerator was used in this study, which produces dual photon energies of 6 and 15 MV as well as eight electron energies ranging between 4.5 and 21 MeV. The % Depth Dose curves were geneated with water scanning equipment at 6, 9, and 15 MeV for 4×4 cm2 and 20×20 cm2 field sizes at SSDS of 100 cm, 108 cm, and 115 cm. According to the measurements from surface to the depth of dose maximum the surface dose increased for all of the electron energies studied at extended SSDS for small field sizes. On the other hand for larger field sizes the surface doses decreased at extended SSDS. It was also observed that the increase in the surface dose diminished as the field size approached to 10×10cm2 then the surface dose started decreasing at extended SSDS as the field sizes increased. Extended SSDS have no observable effect on the tail portion of the depth dose curves.