Theoretical study of the dose measurements reliability with longitudinally arranged dosimetry films in materials with different densities

Investigation purpose. Theoretical study of the depth dose measurements for therapeutic electron beam with longitudinally arranged dosimetry films in materials with different densities. Materials and methods. The work studies how the density of the medium, in which electrons propagate, affects the measured percentage depth dose and its reliability (PDD) . For that, we calculate the distribution of the electron beam dose distribution in homogeneous materials with different densities and in a dosimetry film placed in materials with these densities. The density of material in the calculation varies from 0.4 to 2.3 g/cm3 with a 0.1 g/cm3 step. The coincidence of the PDD within the experimental measurement accuracy, that equals 4% for dosimetry film and 2% for measurements without it, is chosen as the data fitting criterion. Results. The PDD calculated for two geometries and for different media densities is the result of this work. The calculation shows that PDD difference is negligible when the density of the film is equal to the media one. With decreasing of the media density the difference appears in the regions of both shallow and great depth. The PDD is lower for the geometry with film than for geometry without it in case of these densities. When the media density is rising the opposite effect is observed: the PDD in the film is higher than in geometry without film. The maximum range and therapeutic range in both geometries coincide for the calculated curves throughout the range under study. Discussion. The work shows applicability of the investigated method for measurement of the electron beam percentage depth dose in media with densities ranging from 0.9 to 1.8 g/cm3. The results show that PDD measurement method with longitudinally arranged dosimetry films can be applied to determine the maximum range and therapeutic range for media with densities of 0.4 to 2.3 g/cm3, and to measure the half-value depth for media with densities ranging from 0.7 to 2.1 g/cm3.