Dosimetric performance of a multi-point plastic scintillator dosimeter as a tool for real-time source tracking in high dose rate brachytherapy

Purpose: To present the performance of a multi-point plastic scintillation detector (mPSD) as a tool in vivo dosimetry in brachytherapy. Methods: A previously optimized three-point sensor system was used for in vivo HDR brachytherapy measurements (using the scintillators BCF-60, BCF-12, and BCF-10). The light detection system of the mPSD consisted of compactly assembled photomultiplier tubes (PMTs) and dichroic mirrors and filters to achieve a highly sensitive scintillation light collection. The PMT signals were recorded using a NI-DAQ board at a rate of 100 kHz. Dose measurements covering a range of 0.5 to 10 cm from the 192Ir source were carried out according to TG-43 U1 recommendations in order to: (1) characterize the system's response in terms of angular dependence; (2) obtain the relative contribution of positioning and measurement uncertainties to the total system uncertainty; (3) assess the system's temporal resolution; and (4) track the source position in real time. Results: The positioning uncertainty dominated close to the source, whereas the measurement uncertainty dominated at larger distances. A maximum measurement uncertainty of 17 % was observed for the BCF-60 scintillator at 10 cm from the source. The average best compromise between positioning and measurement uncertainties were reached at 17.4 mm. The detector further exhibited no angular dependence. The system provided an average location with a standard deviation under 1.7 mm. The maximum observed differences between measured and expected source location was 1.82 mm. Dose deviations remained below 5% in all the explored measurement conditions. With regard to dwell time measurement accuracy, the maximum deviation observed at all distances was 0.56 s. Conclusions: The performance of the system demonstrated that it could be used for real-time dose, position and dwell time measurements during HDR brachytherapy.