Theoretical investigation of dosimeter accuracy for linear energy transfer measurements in proton therapy: A comparative study of stopping power ratios

Abstract

Background

Accurate measurement of linear energy transfer (LET) is crucial in medical physics, particularly for proton therapy dosimetry. High atomic-number ($Z_{eff}$) materials such as BaFBr and low-$Z_{eff}$ materials such as ${Al}_2{O}_3$ and water are commonly used in dosimeters.

Purpose

To evaluate the feasibility and accuracy of the use of various dosimetry materials (water, air, ${Al}_2{O}_3$, aluminum (Al), BaFBr, and oxygen) for measuring LET by comparing their stopping power (ratios) via the Bethe-Bloch theory and semiempirical models.

Methods

Stopping power ratios were calculated via the PSTAR database for proton energies ranging from 0.01 MeV to 10,000 MeV. The Bethe-Bloch theory with density and shell corrections was used for high-energy protons, whereas a semiempirical model was applied for low-energy protons. Calculations validation involved comparing the computed stopping powers SRIM-2008 and PSTAR for materials such as water, aluminum, air, ${Al}_2{O}_3$, BaFBr, and oxygen.

Results

The stopping power water-to-air ratio remains stable, while the ${Al}_2{O}_3$-to-water and air-to-water ratios highlight their differing attenuation properties. The BaFBr-to-water ratio shows significant material-dependent differences, and the water-to-${Al}_2{O}_3$ ratio is particularly relevant for proton therapy dosimetry calculations in medical physics. These results demonstrate consistency across materials but do not inherently confirm the accuracy of LET measurements. However, a comparison of theoretical models with computed stopping powers SRIM-2008 and PSTAR showed strong agreement, particularly for high-energy protons where the Bethe-Bloch theory was applied, suggesting that the models reliably predict stopping power at these energy levels.

Conclusions

This study confirms the feasibility of using high-$Z_{eff}$ materials such as BaFBr and low-$Z_{eff}$ materials such as ${Al}_2{O}_3$ and water for the use of LET measurements in proton therapy. The results validate the use of the Bethe-Bloch theory, computed stopping powers and semiempirical models in dosimetric applications, enhancing the precision of LET measurements and contributing to improved radiation therapy outcomes.