Determination of average LET of therapeutic proton beams using Al₂O₃:C optically stimulated luminescence (OSL) detectors

Abstract

In this work we present a methodology and proof of concept to experimentally determine average linear energy transfer (LET) of therapeutic proton beams using the optically stimulated luminescence (OSL) of small Al(2)O(3):C detectors. Our methodology is based on the fact that the shape of the OSL decay curve of Al(2)O(3):C detectors depends on the LET of the radiation field. Thus, one can use the shape of the OSL decay curves to establish an LET calibration curve, which in turn permits measurements of LET. We performed irradiations at the M D Anderson Cancer Center Proton Therapy Center, Houston (PTCH), with passive scattering beams. We determined the average LET of the passive scattering beams using a validated Monte Carlo model of the PTCH passive scattering nozzle and correlated them with the shape of the OSL decay curve to obtain an LET calibration curve. Using this calibration curve and OSL measurements, we determined the averaged LET at various water-equivalent depths for therapeutic spread-out Bragg peaks and compared the results with averaged LETs determined using the Monte Carlo simulations. Agreement between measured and simulated fluence-averaged LET was within 24% for low energy spread-out Bragg peak (SOBP) fields and within 14% for high energy SOBP fields. Agreement between measured and simulated dose-averaged LET was within 12% for low energy SOBP fields and within 47% for high energy SOBP fields. The data presented in this work demonstrated the correlation between the OSL decay curve shapes and the average LET of the radiation fields, providing proof of concept of the feasibility of using OSL from Al(2)O(3):C detectors to measure average LET of therapeutic proton beams.

Application of Al 2 O 3 :C+fibre dosimeters for 290 MeV/n carbon therapeutic beam dosimetry

“…The RL response for low-LET carbons in the plateau region of the Bragg curve was found to has LET dependence, while much less than what was observed in the Bragg peak. The Al 2 O 3 :C efficiencies for HCP relative to 60 Co gamma rays obtained in previous studies [33,38] show that the efficiencies values are dependent on the material type and readout technique (thermoluminescence, Continuous Wavelength OSL, Pulsed OSL, Radioluminescence) and even on the choice of filters in front of the PMT. Since the dose deposition for a particular heavy charged particle (HCP) is uniquely defined for a particular material and beam, the differences in the efficiency should only be the result of differences in the dose responses, once the efficiency is a convolution of the response of the material (dose response to a low-LET radiation) and the particular radial dose distribution around the HCP track.…”

Determination of the quenching correction factors for plastic scintillation detectors in therapeutic high-energy proton beams

“…Ideally, it would be great if one can accurately measure the LET for proton beams. Although there are experimental techniques to determine the LET of proton beams (Sawakuchi et al 2010), for the purpose of this study, the LET distributions along depth were calculated by using Monte Carlo simulations. The Monte Carlo code used is the MCNPX 2.6.0 code (Pelowitz 2008), on which a validated nozzle model for the passive-scattering proton beam at the PTCH was used (Titt et al 2008).…”

A real‐time method to simultaneously measure linear energy transfer and dose for proton therapy using organic scintillators

“…[10][11][12] Other detectors, such as thermoluminescence detectors, plastic nuclear track detectors, and other solid state detectors, also can measure LET. 7 Fluorescence nuclear track detectors can determine the LET of individual proton tracks. 13,14 Although these detectors are capable of measuring LET, none can do so in real time, and their designs are too complex for use in daily quality assurance measurements.…”