Characterization of a miniaturized scintillator detector for time-resolved treatment monitoring in HDR-brachytherapy

Abstract

Purpose: HDR brachytherapy combines steep dose gradients in space and time, thereby requiring detectors of high spatial and temporal resolution to perform accurate treatment monitoring. We demonstrate a miniaturized fiber-integrated scintillator detector (MSD) of unmatched compactness which fulfills these conditions. Methods: The MSD consists of a 0.24 mm large and 0.3 mm long detection cell (Gd2O2S:Tb) coupled to a 70-micron outer diameter silica optical fiber. The fiber probe is tested in a phantom using a MicroSelectron 9.1 Ci Ir-192 HDR afterloader. The detection signal is acquired at a rate of 0.08 s with a standard sCMOS camera coupled to a chromatic filter (to cancel spurious Cerenkov signal). The dwell position and time monitoring are analyzed over prostate treatment sequences with dwell times spanning from 0.1 s to 11 s. The dose rate at the probe position is both evaluated from a direct measurement and by reconstruction from the measured dwell position using the AAPM TG-43 formalism. Results: A total number of 1384 dwell positions are analyzed. In average, the measured dwell positions differ by 0.023 ± 0.077 mm from planned values over a 6-54 mm source-probe distance range. The standard deviation of the measured dwell positions is below 0.8 mm. 94 % of the 966 dwell positions occurring at a source-probe inter-catheter spacing below 20 mm are successfully identified, with a 100% detection rate for dwell times exceeding 0.5 s. The average deviation to the planned dwell times is of 0.005 +/- 0.060 s. The instant dose retrieval from dwell position monitoring leads to a relative mismatch to planned values of 0.14 ± 0.7 %. Conclusion: A miniaturized Gd2O2S:Tb detector coupled to a standard sCMOS camera can be used for time-resolved treatment monitoring in HDR Brachytherapy

Six‐probe scintillator dosimeter for treatment verification in HDR‐brachytherapy

“…Measurements within a range of shorter dwell times will be studied in the future. A measurement accuracy of 0.023 ± 0.077 mm has already been shown with a single MSD for dwell times ranging from 0.1 to 11 s 30 …”

“…Finally, note that the individual component of the MPD, referred to as the single‐probe MSD, has already demonstrated its capability in monitoring prostate treatment sequences encompassing dwell times ranging from 0.2 to 11 s 30 . With our probe approach for a MPD, 94% of the 966 dwell positions were successfully identified, with an average deviation to the planned dwell times of 0.005 ± 0.060 and a 100 % detection rate for dwell times exceeding 0.5 s (17%, 86%, 91%, and 95% of the dwell times of 0.2 , 0.3 , 0.4, and 0.5 s were successfully identified, respectively).…”

“…The overall fabrication process is detailed in Refs. [29, 30]. The MPD is locally enlarged to diameters around 320 microns by the presence of the scintillating cells (see Figure 1c).…”

“…Ref. [30]) or by replacing the sCMOS camera by six PMTs which provide higher light detection sensitivity and an acceptable detection speed. However, six (or seven) PMTs may be more expensive than a sCMOS camera.…”

“…26 This indirect dosimetry can be seen to bring the required correction factor. 30 Note that the space-dependent calibration of the organic multipoint detector also relies on the AAPM TG-43 formalism. 25…”