Quantifying the impact of lead doping on plastic scintillator response to radiation

Abstract

Purpose Through the addition of high‐Z dopants, the sensitivity of plastic scintillators to low‐energy radiation can be increased. This study quantifies this change in sensitivity as a function of dopant concentration. Methods Measurements were conducted using four different lead‐doped scintillators (0%, 1%, 1.5%, and 5% Pb) in high‐energy electrons (6 to 15 MeV) and low‐energy photon (100 to 300 kVp) radiation fields. High‐energy and low‐energy irradiations were done using a clinical linear accelerator and an orthovoltage unit, respectively. Light emitted by the scintillator was quantified using a photosensor module. The experimental setup was replicated in Geant4.10.3 Monte Carlo and scintillator parameters (Quenching parameter: kB and the light yield: L0) were varied until agreement between measured and simulated results was reached. Monoenergetic electrons were used to simulate the high‐energy electron beam while a spectrum generated using SpekCalc® software was used in the low‐energy simulations. Light produced by the scintillator was quantified using a flux scorer sensitive only to photons in the visible wavelength range. In order to compare measured and simulated results, the light produced by the scintillator was normalized to the absorbed dose‐to‐water at the point of measurement. Results At high lead dopant concentrations, the scintillator's sensitivity to the 100 kVp beam increased by 474% relative to the 15 MeV electron beam; the scintillator's kB parameter increased from 0.126 to 0.27 mm/MeV. A model quantifying the change in kB and L0 as a function of Zeff was derived; presenting a modified Birks' Law for metal‐doped plastic scintillators. Conclusion The impact of high‐Z doping on plastic scintillator response was quantified; this can allow for the controlled induction of energy dependence in plastic scintillator detectors.

Quantifying Radiobiological Variation in Cancer Radiotherapy Using Monte Carlo Simulation and Doped Plastic Scintillators

“…Given that the densities of all differently doped scintillators are within 5% of one another 49,177 , the LET of electrons traversing the scintillator do not change significantly, allowing the relative to be conserved for a given beam. It is important to note that at this point, the formalism will be presented in a general formthis technique can be conducted with many different detectors as long as they are uniquely energy dependent.…”

“…The light generated by each scintillator used was determined through Birks' Law (Equation 6.1). When using lead doped scintillators, the modified Birks' Law determined by Nusrat et al, 177 should be used to account for the Z-dependence of kB and L 0 . As seen in Equation 6.9, R is a 4 4 matrix, consisting of rows that correspond to the four differently doped plastic scintillators, and columns that correspond to the four LET bins.…”

“…For the light calculation, the kB and L 0 values were obtained from Nusrat et al 177 , and the dE/dx values were obtained from the NIST ESTAR 157 database. Within each LET bin, the visible light generated according to Birks' Law was summated.…”

Monte Carlo modeling of the influence of strong magnetic fields on the stem‐effect in plastic scintillation detectors used in radiotherapy dosimetry

“…Given the extensive physics processes implemented and the accessible nature of these codes, they have great potential in terms of modeling the optical response of PSDs and the impact of the constituent PSD components on the detected signal. For instance, previous studies have utilized GEANT4 in modeling the optical response of scintillation detectors, 32,33 liquid scintillators, 34 and optical fibers 35,36 . In addition, other groups 37–39 have utilized GEANT4 to study the properties of Čerenkov light emission in water for various incident radiation types.…”

“…Given the complexity of the stem‐effect and its dependencies on irradiation conditions and the intrinsic properties of the light guide, 1 careful attention is needed for accurate modeling of this signal in both shape and magnitude. While previous studies 32–36 have successfully used Monte Carlo to model scintillators, PSDs, and optical fibers for various applications, none of these works simulated the stem‐effect in PSDs used for megavoltage photon beam dosimetry in the presence of an external magnetic field. These data would be useful in potentially answering questions raised by recent studies into PSD response in strong magnetic fields 9,18,29 .…”