ESTRO 2025 - Abstract Book

S2683

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Figure 1: (a); Set-up for dose and energy response measurements with layers of white Solid Water®. (b); Close-up view of glass beads on the bolus. (c); Beads sewn onto laminated sheets in a frame for depth-dose profile measurements. (d) Phantom placed in a water bath. Results Type A beads, manufactured by TOHO, emerged as the most suitable to be used as TLDs. They demonstrated agreement with TPS calculations within -0.2% to +2.8% across four treatment plans. Additionally, these beads demonstrated high batch homogeneity (4.8%), high linearity, and minimal energy dependence. To address the reduction in signal observed near the Bragg Peak (Figure 2a), further investigation is needed to establish quenching correction factors.

Figure 2: Depth-dose profile for a (a) pristine Bragg peak at 70MeV and (b) SOBP compared to the measured values of the parallel plate detector at UCLH.

Conclusion The study demonstrates that TOHO beads exhibit promising characteristics as TLDs for proton beam therapy dosimetry. They showed strong agreement with TPS calculations, making them reliable for depth-dose profile measurements, particularly in SOBPs. While quenching effects were observed near the pristine Bragg peak, this limitation is less impactful in clinical settings where SOBP is the standard for proton therapy. With further calibration to refine quenching correction factors, these beads have the potential to offer a cost-effective and versatile solution for accurate dose verification in proton radiotherapy.

Keywords: Proton therapy, dosimetry