Generation of predetermined isodose inclination with the use of a motor driven wedge filter

Abstract

Aim

The aim of this work was to determine an algorithm to obtain a predetermined inclination angle of isodoses for the Saturn 43F linear accelerator with the use of a motor driven wedge filter.

Materials/Methods

It was assumed that a predetermined inclination angle of a reference isodose could be obtained after combining absorbed doses during irradiation with an open field and with a field with a constant 60° wedge. In order to find relations between isodose angles and the irradiation time doses were measured first in a plexiglas phantom and then in a water phantom at the reference depth for the combination of an open field and a field with a 60° wedge. The doses measured under the wedge were normalized with use of the 60° wedge coefficients and converted using tabulated values of the percent depth doses into depth values. Then the angles of isodose slope were calculated.

Results

The results are presented in tables and in figures. The polynomials used to calculate times t₀ and t₆₀ for predetermined isodose angles were obtained.

Conclusions

The polynomials obtained differ from energy to energy. The differences in isodose inclination angles increase with irradiation time using a 60° wedge. The higher is the energy of the beam, the greater is the inclination of the isodoses using the same physical wedge. The differences between the results of measurements in a solid phantom and in a water phantom are due to the differences in depth dose distributions between both materials.