[Influence of cavities on dose distribution in electron depth therapy]

The influence of body cavities on the dose distributions of electrons between 15 and 42 MeV has been studied by means of ionometric and densitometric measurements in polystyrol and cork phantoms. The results show that superelevated doses appear behind the cavities near the surface of the head and the neck caused by scattered electrons of about 10% of the maximum dose in the homogene muscle tissue, particulary by small electron energies. The dose points are spatial very limited with diameters of 1 to 2 cm. With greater depths, i.e. for electron energies of 10, 25 and 42 MeV from 2, 4 and 6 cm respectively, no more superelevated dose caused by the electron scattering appears. All the other body cavities, particulary in the lungs and in the gastrointestinal tract, have for that reason an influence on the dose distribution essentially by the electron radius increased with the cavity length. The electron scattering and the organ motions provide for an great dose equalization.