Determination of the virtual electron source of a betatron.

The definition and use of the virtual source point of an electron beam are discussed and a new method of measuring the virtual source point using a multi-pinhole camera is described. Application examples are given for a 42 MeV betatron.

[An analytical method to calculate electron dose distributions. Part I: Method (author's transl)]. / Ein analytisches Verfahren zur Berechnung von Elektronendosisverteilungen. Teil I: Das Verfahren.

A method for the calculation of electron dose distributions is described. The dose distributions of stationary electron beams in water are represented by formulas for depth dose curves and transverse distributions. Curved surfaces, oblique incidence of rays, and inhomogeneities are taken into account by applying the law of distance and the method of equivalent thicknesses of water layers. A detailed program is given to calculate the electron dose distributions in that plane of the central ray which is at right angle to the theoretical circle plane of a 42 MeV betatron.

[Consideration of large in homogeneous regions of the computation of electron dose distributions]. / Berücksichtigung grosser Inhomogenitätsbereiche bei der Berechnung von Elektronendosisverteilungen

A simple method, suggested by Laughlin and Pohlit for calculation of dose distribution in electron beams which is considering the nonhomogeneous structure of the body, has been examined with regard to its accuracy within the energy range up to 42 MeV. Thereby, the dose distributions calculated and measured over nonhomogeneous thorax phantoms were compared. The method is based on the dose in homogeneous muscular tissue for a depth of area-weight identical to that in nonhomogeneous tissue with corrections being made according to the law of squared distances. Thus, only the loss of electron energy but not the scattering is considered. Smaller nonhomogeneous zones are completely neglected, larger ones treated as regions of equal density. The present study of the region of the lung and previous papers concerning bones [13] and cavities [11] show that the method, apart from near surface cavities, yields a satisfying exactness of the calculated dose distributions. If larger inhomogeneities - especially of the lung - are regarded, their mean tissue density, their shape, size and location ought to be known as exactly as possible.

[Influence of cavities on dose distribution in electron depth therapy]. / Zum Einfluss von Hohlräumen auf die Dosisverteilung in der Elektronen-Tiefentherapie

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.