On the use of a single‐fiber multipoint plastic scintillation detector for ¹⁹²Ir high‐dose‐rate brachytherapy

Abstract

Purpose: The goal of this study was to prove the feasibility of using a single-fiber multipoint plastic scintillation detector (mPSD) as an in vivo verification tool during 192 Ir high-dose-rate brachytherapy treatments. Methods: A three-point detector was built and inserted inside a catheter-positioning template placed in a water phantom. A hyperspectral approach was implemented to discriminate the different optical signals composing the light output at the exit of the single collection optical fiber. The mPSD was tested with different source-to-detector positions, ranging from 1 to 5 cm radially and over 10.5 cm along the longitudinal axis of the detector, and with various integration times. Several strategies for improving the accuracy of the detector were investigated. The device's accuracy in detecting source position was also tested. Results: Good agreement with the expected doses was obtained for all of the scintillating elements, with average relative differences from the expected values of 3.4 ± 2.1%, 3.0 ± 0.7%, and 4.5 ± 1.0% for scintillating elements from the distal to the proximal. A dose threshold of 3 cGy improved the general accuracy of the detector. An integration time of 3 s offered a good trade-off between precision and temporal resolution. Finally, the mPSD measured the radioactive source positioning uncertainty to be no more than 0.32 ± 0.06 mm. The accuracy and precision of the detector were improved by a dose-weighted function combining the three measurement points and known details about the geometry of the detector construction. Conclusions: The use of a mPSD for high-dose-rate brachytherapy dosimetry is feasible. This detector shows great promise for development of in vivo applications for real-time verification of treatment delivery.

A review of recent advances in optical fibre sensors forin vivodosimetry during radiotherapy

“…In a further study, Therriault-Proulx et al 57 developed a single fibre, multipoint, plastic scintillator for iridium-192 HDR brachytherapy treatment verification in a water phantom. This scintillator contained a three-point detector system comprising BCF-10, BCF-12 and BCF-60 scintillating elements.…”

“…It has been proposed as a suitable dosemeter for in vivo brachytherapy applications, owing to its small size and sufficient sensitivity. 56,57 The difficulty in efficiently coupling the plastic scintillator to the optical fibre is one of the main disadvantages of these types of dosemeters. The probe was further tested for use in monitoring urethral doses during HDR brachytherapy for prostate cancer treatment.…”

In vivodosimetry: trends and prospects for brachytherapy

“…Occasional IVD feasibility studies have also been conducted in some clinics. [12][13][14][15][16][17][18][19][20][21][22][23][24] However, routine implementations of IVD for error detection monitoring and QA of the BT treatments is yet to come. One reason for this may be that the cost vs benefit relation of IVD is not established and that robust IVD systems that do not leave a significant footprint on the treatment workflow are not commercially available.…”

“…Similar concepts have been implemented during phantom measurements. 14,18,22,25,85 Nakano et al 86 adapted statistically based discrepancy criteria during phantom experiments using HDR BT sources, where the discrepancy was based on measured and expected source coordinates rather than on dose rates.…”

“…A multipoint plastic scintillation detector (mPSD) using three scintillator elements (Figure 1) 18 A weighting function that accounts for the difference in signal-to-noise ratio between multiple measurement points was tested for BT source irradiations at source-todetector radial distances (r) from 1 to 5 cm and for a range over 10 cm along the longitudinal axis (z). The measurements demonstrated a reliable way to improve the error detection capacity of the mPSD.…”