ESTRO 2024 - Abstract Book

S3409

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Results:

Figure 1A shows the netto extinction of the Fricke solution as a function of dose for different beam qualities The slopes of the linear regression from figure 1A are listed in table 1. For 149 MeV/u carbon ion the response exhibits the smallest slope and photons (6MV-X) have the largest slope. As it can be seen from figure 1A, the concentration of Fe(III)-ions is different for different LETs. In table 1, additionally to the slopes of the linear regression from figure 1, the G-value of Fe(III)-ions calculated from them are given, as well as those, of the corresponding simulations. The simulated G-value for 149 MeV/u carbon ions is equal to the experimentally determined G-value within the limits of uncertainty. Simulated G-values of the other radiation types and energies are significantly smaller than the experimental G-values, but they also indicate an LET-dependence. Figure 1B shows the response of the FRICKE solution for larger dose levels of up to 1000Gy in the modulated carbon ion beam. The LET-dependence can also be seen here.

Figure 1: (A) Dependence of netto extinktion on the applied dose investigated for different beam qualities. The uncertainties are derived from the standard deviation over four measured values. (B) Dependence of applied dose on the netto extinktion investigated for modulated carbon ion beam with different positions in WED of a spread-out Bragg peak and the entrance channel. Position 1: 10mm WED. Position 2: 31mm WED.

Table 1: Slopes of the different beam qualities from figure 1A, as well as the corresponding determined and simulated G-values.

Type of radiation and energy

Slope [1/Gy]

Experimental G-value from the slope [µmol/J]

TOPAS-nBio simulation G-value [µmol/J]

Photons (6 MV-X)

0.00386 (19)

19.3 (1.0)

14.11 (6) 14.23 (6) 15.13 (3)

Protons (221 MeV/u) Protons (80 MeV/u)

0.00329 (9)

16.4 (5)

0.00347 (34) 0.00325 (13) 0.00250 (10)

17.3 (2.0)

Carbon ions (430 MeV/u) Carbon ions (149 MeV/u)

16.6 (7) 12.5 (5)

13.1500 (18) 11.9007 (35)

Carbon ions (320 MeV/u), position 1

0.00115 (10)