Plastic scintillation detectors are increasingly used to measure dose distributions in the context of radiotherapy treatments. Their water-equivalence, real-time response and high spatial resolution distinguish them from traditional detectors, especially in complex irradiation geometries. Their range of applications could be further extended by embedding scintillators in a deformable matrix mimicking anatomical changes. In this work, we characterized signal variations arising from the translation and rotation of scintillating fibers with respect to a camera. Corrections are proposed using stereo vision techniques and two sCMOS complementing a CCD camera. The study was extended to the case of a prototype real-time deformable dosimeter comprising an array of 19 scintillating fibers. The signal to angle relationship follows a gaussian distribution (FWHM = 52°) whereas the intensity variation from radial displacement follows the inverse square law. Tracking the position and angle of the fibers enabled the correction of these spatial dependencies. The detecting system provides an accuracy and precision of respectively 0.08 mm and 0.3 mm on the position detection. This resulted in an uncertainty of 2° on the angle measurement. Displacing the dosimeter by ±3 cm in depth resulted in relative intensities of 100 ± 10% (mean ± standard deviation) to the reference position. Applying corrections reduced the variations thus resulting in relative intensities of 100 ± 1%. Similarly, for lateral displacements of ±3 cm, intensities went from 98 ± 3% to 100 ± 1% after the correction. Therefore, accurate correction of the signal collected by a camera imaging the output of scintillating elements in a 3D volume is possible. This work paves the way to the development of real-time scintillator-based deformable dosimeters.
Anatomical motion and deformation pose challenges to the understanding of the delivered dose distribution during radiotherapy treatments. Hence, deformable image registration (DIR) algorithms are increasingly used to map contours and dose distributions from one image set to another. However, the lack of validation tools slows their clinical adoption, despite their commercial availability. This work presents a novel water-equivalent deformable dosimeter that simultaneously measures the dose distribution and tracks deformation vector fields (DVF). The dosimeter in made of an array of 19 scintillating fiber detectors embedded in a cylindrical elastomer matrix. It is imaged by two pairs of stereoscopic cameras tracking the position and angulation of the scintillators, while measuring the dose. The resulting system provides a precision of 0.3 mm on DVF measurements. The dosimeter was irradiated with 5 × 3, 4 × 3 and 3 × 3 cm2 6 MV photon beams in both fixed and deformed conditions. The measured DVF was compared to the one computed with a DIR algorithm (Plastimatch). The deviations between the computed and measured DVFs was below 1.5 mm. As for dose measurements, the dosimeter acquired the dose distribution in fixed and deformed conditions within 1% of the treatment planning system calculation and complementary dose validation using the Hyperscint dosimetry system. Using the demonstrated qualities of scintillating detectors, we developed a real-time, water-equivalent deformable dosimeter. Given it’s sensor tracking position precision and dose measurements accuracy, the developed detector is a promising tools for the validation of DIR algorithms as well as dose distribution measurements under fixed and deformed conditions.
Systematic characterization of semiconductor colloidal quantum dots (cQDs) response to ionizing radiation must be performed to use them in radiation detection. In this study, the robustness of multi-shell (MS) and core/shell (CS) cQDs was investigated under irradiation. Radioluminescence (RL) measurements with kV and MV photon beams revealed a better resistance of MS cQDs to ionizing radiation, with their spectra fluctuating by barely ∼ 1 nm. A systematic signal recovery between subsequent irradiations was noticed for MS cQDs only. A beam energy dependence of the RL stability was detected between kV and MV energies. At the same point of dose cumulated, the RL signal loss for the kV beams was observed to be ∼6-7% smaller than that of the MV beam, for both types of cQDs. These results demonstrate that MS cQDs are better candidates as ionizing radiation sensors than CS cQDs, especially in the kV energy range.
Purpose Cherenkov radiation carries the potential of direct in‐water dose measurements, but its precision is currently limited by a strong anisotropy. Taking advantage of polarization imaging, this work proposes a new approach for high‐accuracy Cherenkov emission dose measurements. Methods Cherenkov radiation produced in a 15 × 15 × 20‐cm3 water tank is imaged with a cooled charge‐coupled device (CCD) camera from four polarizer transmission axes [0, 45, 90, 135°]. The water tank is positioned at the isocenter of a 5 × 5‐cm2, 6‐, and 18‐MV photon beam. Using Malus’ law, the polarized portion of the signal is extracted. Corrections are applied to the polarized signal following azimuthal and polar Cherenkov emission angular distributions extracted from Monte Carlo simulations. Projected percent depth dose and beam profiles are measured and compared with the prediction from a treatment planning system (TPS). Results Corrected polarized signals on the central axis reduced deviations at depth (mean ± standard deviation) from 8% ± 5% to 0.8% ± 1% at 6 MV and 8% ± 7% to 1% ± 3% at 18 MV. For the profile measurement, differences between the corrected polarized signal and the TPS calculations are 1% ± 3% and 2% ± 3% on the central axis at 6 and 18 MV respectively. In these conditions, Cherenkov emission is shown to be partly polarized. Conclusions This work proposes a novel polarization imaging approach enabling high‐precision water‐based dose measurements using the Cherenkov radiation. The method allows a correction of the Cherenkov emission anisotropy within 4% on the beam central axis and in depth.
Purpose: This study intends to characterize the energy dependence of the effect of radiation damage on CdSe multi‐shell (MS) (CdS/CdZnS/ZnS) and CdSe core/shell (CS)(ZnS) cQDs. It also aims to investigate irregularities resulting of pauses between subsequent irradiations. Methods: Radioluminescence (RL) measurements were performed with a CCD camera as dose was cumulated by the cQDs (up to 10 kGy), for beam energies 120 kVp, 220 kVp and 6 MV. Repeated expositions of 1999 MU were cumulated. Pauses between subsequent irradiations were varied from 2 to 50 minutes. cQDs photoluminescence (PL) and RL spectral stability was tracked by quantifying the position and FWHM of the luminescence peak. Results: Both types of cQDs showed a clear energy dependence of the RL signal decrease between the kV and the MV beams. For 1.2 kGy of dose cumulated, MS cQDs had 92% of the initial signal left at 6 MV compared to 98% at 120 kVp. The same was observed for CS cQDs: 87% at 6 MV vs 94% at 120 kVp. MS cQDs were found to have a systematic (though small, ∼1%) RL intensity recovery for pauses of 15 minutes or more, while CS cQDs maintain a stable loss regardless of the pause duration. PL and RL spectral measurements revealed a good stability (< 1% variation of the peak position and FWHM) for both types of cQDs. Conclusion: In all, both MS and CS cQDs have a sufficient resistance to large doses of radiation for standard radiation therapy and imaging. Since this resistance is better for lower energy, the utilization of cQDs could be optimized for low energy applications (e.g. theragnostic applications for small animal studies and others). Finally, the ionizing radiation damage mechanisms for this new type of nano‐scintillator still have to be identified properly.
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