In Vivo Verification of Treatment Source Dwell Times in Brachytherapy of Postoperative Endometrial Carcinoma: A Feasibility Study

Abstract

(1) Background: In brachytherapy, there are still many manual procedures that can cause adverse events which can be detected with in vivo dosimetry systems. Plastic scintillator dosimeters (PSD) have interesting properties to achieve this objective such as real-time reading, linearity, repeatability, and small size to fit inside brachytherapy catheters. The purpose of this study was to evaluate the performance of a PSD in postoperative endometrial brachytherapy in terms of source dwell time accuracy. (2) Methods: Measurements were carried out in a PMMA phantom to characterise the PSD. Patient measurements in 121 dwell positions were analysed to obtain the differences between planned and measured dwell times. (3) Results: The repeatability test showed a relative standard deviation below 1% for the measured dwell times. The relative standard deviation of the PSD sensitivity with accumulated absorbed dose was lower than 1.2%. The equipment operated linearly in total counts with respect to absorbed dose and also in count rate versus absorbed dose rate. The mean (standard deviation) of the absolute differences between planned and measured dwell times in patient treatments was 0.0 (0.2) seconds. (4) Conclusions: The PSD system is useful as a quality assurance tool for brachytherapy treatments.

Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

“…Energy deposited per history in the detector (eV/history) ~3 × 10 11 s histories 1 It differs slightly from the recommended in report ICRU 90 [28]. 2 Recommended in supplement 2 for the 2004 update of the AAPM Task Group No. 43 Report [6].…”

“…The core of the PSD is synthesized with polystyrene and fluorescent dopants, and the cladding is made of PMMA. Signal processing and analysis was described in a previous work [ 2 ]. The phantom measurements were carried out in a 10 cm × 10 cm cylindric PMMA phantom.…”

“…For the three ratios, the uncertainties corresponding to the phantom composition, density, and materials' cross-sections are considered the same. 2 Only the Type A uncertainty component was considered based on 10 consecutive acquisitions. 3 This result was obtained in the same conditions as the polystyrene ratio except for the detector material: water instead polystyrene.…”

“…Other causes of deviations correspond to uncertainties in IVD [ 1 ]. Some detector uncertainties, such as repeatability, signal-to-noise ratio, linearity, and precision of dwell time measurements in patient treatments, were reported in relation to a plastic scintillator detector (PSD) for brachytherapy IVD in a previous study [ 2 ]. There are also other important issues, such as detector calibration and its energy, temperature, and angular dependence, that need to be characterized for use in routine clinical practice.…”