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

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-Zeff 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 BetheBloch 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-Al2O3 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-Zeff materials such as BaFBr and low-Zeff 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.