# The Performance of LiF:Mg-Ti for Proton Dosimetry within the Framework of the MoVe IT Project
## 3 Results and Discussion  
The depth-dose profiles resulting from the irradiation of the TLD rows are shown in Figure 2. Figure 2b (second experiment) shows an energy shift that resulted in a peak shift between the two TLD rows of about 7 mm, as we expected. The first and the second experiments provided an entrance dose into the bio-phantom of 0.7 Gy, corresponding to a peak dose of 1.5 Gy for both rows. In the third experiment (Figure 2c), the entrance dose measure was 0.9 Gy, while for the fourth experiment (Figure 2d) it was 0.5 Gy (corresponding to peak doses of 1.5 Gy and 0.8 Gy, respectively). The depth-dose profile in Figure 2c shows a peak shifted at a lower depth than the other ones. A variation in the setup using a larger thickness for the water-equivalent slab phantom (RW3 slab phantom) affected the peak position, which was correctly detected by the dosimeters. The depth-dose profiles obtained with TLDs-100 using the same geometrical configuration and beam parameters (first and second irradiation-row 1) are compared in Figure 3.  
Figure 1: (**a**) Design of the bio-phantom implemented by the BioTech (UniTN) partner, containing both thermoluminescent dosimeters (TLDs-100) and cells. (**b**) Bio-phantom with an array of TLDs and cells included in the gelatine. (**c**) Bio-phantom ready for irradiation with the beam entering orthogonally. High dose differences occurred in the distal fall-off region of the Bragg peak, while lower deviations were observed elsewhere. A combination of several factors relating both to dosimeter characteristics and the proton beam dose profile can result in the deviation observed between the two measurements. First, the relative dose efficiency of TLDs depends on the activator (Mg, Ti) concentrations, batch-to-batch variations, and on the annealing process; thus, it should be determined for the TLD batch used in each specific dose measurement. In addition, the TLD efficiency for measuring the absorbed dose drops off as the linear energy transfer of the charged particles increases [40; 41; 42; 43]. In the study by [PERSON] et al. [30], the dose measurements using TLD-100 in a proton beam in the distal fall-off region were accurate to within \(\pm\)5.0%. The  
Figure 3: Comparison between proton beam depth–dose profiles reconstructed with the thermoluminescent dosimeters (TLDs-100) from row 1 in the 1 st and 2 nd irradiation stages. Figure 2: Depth–dose profiles of the proton beam in a bio-phantom provided by the thermoluminescent dosimeters (TLDs-100): (**a**) first irradiation stage: two TLDs’ rows irradiated simultaneously; (**b**) second irradiation stage: two TLDs’ rows irradiated one at time, the second one with a planned energy shift; (**c**,**d**) third and fourth irradiation stages: one TLD’s row irradiated at different Bragg peak dose. data measured are in good agreement with the data from the literature, but it is important to point out that a comparison of the efficiency values gathered from different groups has to be performed very carefully owing to the different readout and evaluation procedures used by the research groups. On the other hand, the reproducibility of the experiment is more critical in the steeply descending region downstream of the Bragg peak, while the flatness region is such that the TLD positioning accuracy has less impact on the absorbed dose variation. The knowledge of the Bragg peak position plays a key role in the correct delivery of proton therapy, since the setup uncertainties influence the proton range and dose distribution [44; 45]. For this reason, the only strategy that can be used to catch treatments errors, assist in treatment adaptation, and record the actual dose delivered to the patient is the in vivo dosimetry (IVD); however, IVD is not used routinely for proton radiation therapy, despite physical and technical quality assurance protocols having been proposed and clinically investigated [46].