ESTRO 2024 - Abstract Book

S3237

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Different proton energies (110, 130, 160, 190, 205, 220 MeV) were delivered according to t RS and residual ranges ( R res ) were extracted ( R res = R 80, RS - WET RS ). To investigate the influence of the MF, all measurements were repeated without the MR scanner in place (i.e., at IS ext ). To compensate for the inhomogeneity of the EBT3 film response and lateral film scanner effect, a pixel-by-pixel background fog subtraction (PPS) 4 approach was implemented for pixel-wise dose calculation. A 2D Gaussian fit was then applied to compute maximum and minimum lateral standard deviation of dose spots ( σ max and σ min ) and eccentricity ( ϵ ) 1 .

Results:

The introduction of RSs resulted in the following WET : A, 69.8 mm; AB, 145.4 mm; ABC, 203.6 mm. In presence of the MF, RSs positioned at d RS of 7 cm allowed for a reduction in beam width compared to the scenario without RS, at each R res value ( Figure 2.a ). Thicker RSs exhibited a more pronounced reduction in ϵ (mean Δ ϵ : A, -13.83 ± 2.05%; AB, -34.27 ± 2.59%; ABC, -52.02 ± 2.21%) ( Figure 2.b ). Furthermore, a decrease in d RS proved a significant effect on beam width reduction (mean ΔS spot : -45.07 ± 7.19% at 7 cm and -26.30 ± 7.75% at 11 cm, compared to 15 cm) ( Figure 2.c ). The effects of thickness and placement of RSs on beam width were similar to what was observed in absence of the MF (mean ΔS spot with MF at the lowest R res : A, -2.30 ± 1.45%; AB, -2.43 ± 0.42%; ABC, -1.93 ± 0.75%). However, under the influence of the MF, σ max and σ min were distinguished by a larger variety ( Figure 2.d ). Besides, at each R res value, RSs led to a decrease in beam path deflection.