The geometry of the Siemens KD2 accelerator shown in fig.6 consists of an exit vacuum window, primary collimator, scattering foils, a beam monitor ion chamber, a mirror, x and y jaws, and electron applicators which are solid-walled flat tubes made of aluminium with scrapers of brass, steel and aluminium. The experimental data are from Joanna Cygler of Ottawa Regional Cancer Center (6 and 11 MeV) and from Jack Janssen and Henk Huizenga of the Dr Daniel den Hoed Cancer Clinic Netherlands (21 MeV beam). We have also tried to simulate other beams with higher energies from the Ottawa clinics KD2 but we are unable to reproduce the measured high bremsstrahlung tail. This may be due to our lack of an accurate description of the scattering foils of the accelerator for these higher energies.
Figures 26, 27 and 28 show the energy spectra and angular distributions of electrons and contaminant photons and dose distributions along with dose components contributed from each beam defining component for 6, 11 and 21 MeV electron beams respectively.
The dose measurements (6 and 11 MeV beam) have been done with a small diode detector. The 21 MeV beam data have been measured with an NACP plane parallel ionization chamber, using the NACP protocol to convert ionization to dose.
Excellent agreement is obtained between calculated and measured central-axis depth-dose curves for these beam energies except for the photon tail of the 21 MeV beam which is underestimated.
Figure 29 presents calculated
dose profiles at the phantom surface and at 
from various
components of an 11 MeV beam from the KD2 accelerator.
Due to the applicator design of the KD2 there are more scattered electrons near the field boundary than near the central-axis. The dose profiles contributed by electrons scattered from the applicator become flatter at larger depth because scattered electrons from the applicator have lower energy and relatively large angle.