Response analysis of TLD-300 dosimeters in heavy-particle beams

Abstract

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65) + Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (150 degrees C) and peak 5 (250 degrees C) response of CaF2:Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental 12C heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to 60Co, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the 60Co reference radiation to the 12C heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

LET dependence of thermoluminescent efficiency and peak height ratio of CaF2:Tm

“…Their data were related to absorbed dose to muscle tissue. Loncol et al (1996) measured peak efficiencies (relative to absorbed dose to water) for an 85 MeV proton beam, thereby complementing the findings of this work in qualitatively good agreement. An in-depth intercomparison of TLD-300 efficiencies determined by different authors can be found in Berger and Hajek (2007).…”

“…Considering the non-uniform pattern of dose deposition at the microscopic level, the enhanced sensitivity of peak 5 to HCP irradiation can be explained by its linear-supralinear dose response (Olko, 1998(Olko, , 2007. Several authors have proposed to exploit this increased sensitivity to high linear energy transfer (LET) radiation for neutron-gamma ray discrimination (Loncol et al, 1996) and HCP dosimetry (Hoffmann and Prediger, 1983;Loncol et al, 1996).…”

AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs

“…The different peaks in the glow curves of certain TLD materials show different sensitivities to the LET of the incident radiation. Correspondingly, the relative peak intensity can be used to measure the LET in mixed radiation fields or heavy particle beams …”

“…Correspondingly, the relative peak intensity can be used to measure the LET in mixed radiation fields 125,126 or heavy particle beams. 127…”

Dual‐storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer

“…Proton LET is notoriously difficult to measure directly with only a very limited number of devices commercially available such as the tissue-equivalent proportionality counter (TEPC), 19 silicon spectrometer, 20 or CR-39 etch detectors. 21 Other authors have presented creative strategies for simultaneous proton dose and LET measurements such as the use of organic scintillators, 22 thermoluminescent dosimeters 23,24 (TLDs), Al 2 O 3 :C OSLD 25 detectors, and Gafchromic EBT3 films. 26 In this work, we present a novel solution to this problem by proposing the use of a proton energy dependent high Z eff storage phosphor (Z eff = 49, BaFBr 0.85 I 0.15 :Eu 2+ ) in conjunction with a near-proton energy independent low Z eff storage phosphor (Z eff = 18, KCl:Eu 2+ ).…”