Optically stimulated luminescence detectors for dosimetry and LET measurements in light ion beams

Abstract

Objective: This work investigates the use of Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) detectors to determine both the dose and the radiation quality in light ion beams. The radiation quality is here expressed through either the linear energy transfer (LET) or the closely related metric Qeff, which depends on the particle's speed and effective charge. The derived LET and Qeff values are applied to improve the dosimetry in light ion beams.

Approach: OSL detectors were irradiated in mono-energetic 1H−, 4He−, 12C−, and 16O−ion beams. The OSL signal is associated with two emission bands that were separated using a pulsed stimulation technique and subjected to automatic corrections based on reference irradiations. Each emission band was investigated independently for dosimetry, and the ratio of the two emission intensities was parameterized as a function of fluence- and dose-averaged LET, as well as Qeff. The determined radiation quality was subsequently applied to correct the dose for ionization quenching.

Main results: For both materials, the Qeff determinations in 1H− and 4He−ion beams are within 5 % of the Monte Carlo simulated values. Using the determined radiation quality metrics to correct the non-linear (ionization quenched) detector response leads to doses within 2 % of the reference doses. 

Significance: Al2O3:C and Al2O3:C,Mg OSL detectors are applicable for dosimetry and radiation quality estimations in 1H- and 4He-ions. Only Al2O3:C,Mg shows promising results for dosimetry in 12C-ions. Across both materials and the investigated ions, the estimated Qeff values were less sensitive to the ion type than the estimated LET values. The reduced uncertainties suggest new possibilities for simultaneously estimating the physical and biological dose in particle therapy with OSL detectors.

Optically stimulated luminescence dosimeters for simultaneous measurement of point dose and dose-weighted LET in an adaptive proton therapy workflow

“…The good agreement between simulated and measured doses is a result of the high readout precision (< 1%) achievable with OSLDs, and the relatively low quenching correction factors (< 10%) estimated from the determined LET D . This is in contrast to OSLD dosimetry in carbon ion beams, where the quenching correction can exceed 50% and is the main contribution to the dose uncertainty with OSLDs ( 10 ).…”

“…Among the available detector types, particularly the use of optically stimulated luminescence detectors (OSLDs) is attractive for in-phantom measurements due to the possibility of creating ultra-thin detectors (< 100 µm) that can be cut to arbitrary shapes ( 7 ). While previous studies have determined the dose and LET with OSLDs in proton beams under reference conditions, we demonstrate for the first time how these quantities can be measured in the mixed particle fields relevant to SOBPs to validate adaptive radiotherapy ( 8 – 10 ). Although the LET can be averaged in different ways, in our work we always refer to the dose-weighted LET (LET D ) with contributions from protons only.…”

“…The use of the OSLD emission band ratio to determine LET D has been demonstrated for protons, helium, and carbon ions up to 41.3 keV/μm in water. For ions heavier than carbon, the dense ionizations cause a signal saturation, and the emission band ratio is difficult to relate to the LET ( 10 ). The estimated LET D can in turn be used to look up the relative detector efficiency in Figure 3B to correct ionization quenched dose in the OSLD.…”

“…The estimated LET D can in turn be used to look up the relative detector efficiency in Figure 3B to correct ionization quenched dose in the OSLD. Hence, a single OSLD permits to determine the dose and average LET simultaneously ( 8 , 10 ).…”

Assessment of fluence- and dose-averaged linear energy transfer with passive luminescence detectors in clinical proton beams

“…That approach was used to simultaneously determine LET and dose with OSLD measurements in an anthropomorphic head phantom to validate a treatment plan for adaptive proton therapy (Bobić et al 2024). The measurement technique has been extended to helium and carbon ions with both Al 2 O 3 :C and Al 2 O 3 :C,Mg OSLDs (Christensen et al 2023).…”