The changes of beam specification parameters along the normal central axis of electron beams with increasing gantry angle had been measured. The electron beams were produced by Varian Clinac2100C with energies of 6, 9, 12, 16, and 20 MeV. This work was performed using Wellhőffer water phantom provided with two small cylindrical IC-15 chambers. It was found that the oblique incidence beams cause the dmax depth, Rp, R85 at normal central axis shifted to skin surface. For all energies, the changes of gantry angle from 0 to 20 shift the dmax depth in the range of 2.0 % up to 17.73 %, Rp in the range of 2.02 up to 10.78 %, and R85 in the range of 8.93 up to 9.37 %. The percentage ionization along the diagonal fanline was also measured. The results indicated that for lower energy electron beams (6 MeV, 9 MeV, and 12 MeV) the diagonal fanline was still located at the penumbra region (80 % -20% isodose line), whereas for higher energies (16 MeV and 20 MeV) these diagonal fanline were in radiation field area particularly for the gantry angle of 15° and 20°.
|Number of pages||4|
|Publication status||Published - 1 Jan 2007|
|Event||10th World Congress on Medical Physics and Biomedical Engineering, WC 2006 - Seoul, Korea, Republic of|
Duration: 27 Aug 2006 → 1 Sept 2006
- Diagonal fanline
- Electron beams
- Oblique incidence