Improved simultaneous LET and dose measurements in proton therapy

Abstract

The objective of this study was to improve the precision of linear energy transfer (LET) measurements using $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4–6.5) $$\hbox {keV}\, \upmu \hbox {m}^{-1}$$ keV μ m - 1 range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV ($$F^+$$ F + -center) emission bands of $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

Characterisation and Quenching Correction for an Al2O3:C Optical Fibre Real Time System in Therapeutic Proton, Helium, and Carbon-Charged Beams

“…This effect strongly affects the LET D for small step sizes (<500 µm) because Monte Carlo codes usually only consider collisions where the kinetic energy imparted to secondary electrons is below a given threshold, restricting the quantity to shorter-range electrons and giving better characterisation when one wants to correlate the radiation effects to RBE or microdosimetry [ 47 ]. This step-limiting effect was studied by Guan et al [ 46 , 48 ] and further addressed and used by other authors [ 18 , 29 , 49 , 50 , 51 ]. The agreement is that the step limit effect is negligible for LET f although it strongly affects LET D results [ 52 , 53 ].…”

“…One class of promising dosimeters is based on luminescence detectors. One advantage is the diverse (point, 1D, 2D) readout possibilities, both as active (radioluminescence-RL, scintillation) and as passive detectors (thermoluminescence-TL, optically stimulated luminescence-OSL and radiophotoluminescence-RPL) [ 5 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. One known drawback of luminescence detectors is the existence of the quenching effect [ 21 ], which is the dose nonlinearity effect caused by the high ionisation density in particles of high LET, i.e., the higher the particle LET, the lower the light production efficiency from the luminescence detector, resulting in substantially under-estimated doses [ 22 , 23 , 24 , 25 , 26 , 27 ].…”

Ultra-high dose rate dosimetry for pre-clinical experiments with mm-small proton fields

“…The dose calibration, preparation, and readout procedures are described in [36]. Although the OSLDs are capable of simultaneous dose and LET measurements [47], which allows for ionization quenching corrections, no quenching corrections were applied to the doses due to the high proton energies with a negligible quenching.…”

Sensitivity correction of fluorescent nuclear track detectors using alpha particles: Determining LET spectra of light ions with enhanced accuracy

“…15 In the case of optically stimulated luminescent (OSL) detectors (OSLDs), both the shape of the OSL decay curve and the ultraviolet-to blueemission intensity ratio of aluminum oxide doped with carbon have been proposed and applied to measure LET in PT. [16][17][18] Alternatively, silicon-based detectors have also been tested for LET measurements in PT and IBT. 19 A rather novel and promising type of detectors, which have been used for LET measurements on proton and ion beams, are fluorescent nuclear track detectors (FNTDs).…”

“…In addition, exploiting the different relative efficiencies (defined as TL‐signal per unit of absorbed dose) of two lithium fluoride‐based TLDs having different dopants, LET distributions in‐depth were measured on a clinical proton spread out Bragg peak 15 . In the case of optically stimulated luminescent (OSL) detectors (OSLDs), both the shape of the OSL decay curve and the ultraviolet‐ to blue‐emission intensity ratio of aluminum oxide doped with carbon have been proposed and applied to measure LET in PT 16–18 . Alternatively, silicon‐based detectors have also been tested for LET measurements in PT and IBT 19 .…”