ESTRO 2024 - Abstract Book

S3353

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

the largest cone with 25 mm diameter as the machine specific reference (msr) field, the individual perturbation factors attributed to the (1) detector’s housing, (2) material of detector’s sensitive volume; and (3) dimension of the sensitive volume, are computed according to equations 1, 2 and 3, respectively.

Results:

At 7 mm depth, both the dosimetric field sizes (full-width at half maximum, FWHM) acquired with the microSilicon detector and EBT3 films amount of 3.0 mm. The FWHM values as well as the penumbra (defined as the distance between 20 % and 80 % of the normalized profile) at all measurement depths agree within 0.1 mm between both measurements. Figure 1 shows the comparisons of the measured (left) and simulated (right) normalized dose profile (film or water voxel) and microSilicon’s signal profile for the 3 mm field size at 7 mm depth. In both measurements and simulations, a small but observable broadening of the microSilicon’s signal profile can be asserted.

The output ratio measured using the microSilicon, normalized to the 25 mm cone, amounts to 0.4466 ± 0.0224 that agrees, within the measurement uncertainty, to the output factor measured by the films of 0.4434 ± 0.0222.

On the one hand, the simulation of the perturbation effects showed a small detector’s over-response due to the material of the housing and of the sensitive volume with enhanced-density. On the other hand, the volume-averaging effect caused by the dimensions of the sensitive volume gives rise to an under-response that is partially compensated by the former effect. As the result, the total output correction factor of the microSilicon detector for the 3 mm cone was determined to be of 1.0333(11).