This communication presents an instrumental development based on the printed circuit board (PCB) technology to integrate electrochemiluminescence (ECL) analysis in microfluidic systems. PCB gold macro- (10 mm²) and micro- (0.09 mm²) electrodes and two ECL microfluidic devices are designed, fabricated and tested via luminol ECL detection. Potential modulation is performed between 0.7 and 0 V vs. Ag/AgCl for luminol oxidation, thus giving rise to on/off ECL responses in the presence of hydrogen peroxide. Synchronous detection is adopted to allow weak ECL signal recovery at a very low signal-to-noise ratio (SNR). The detection limit obtained with the two ECL microfluidic devices is 50 nM and 100 nM H₂O₂ for macroelectrodes and microelectrodes, respectively.

Purpose To develop a novel instrument for real-time quality assurance (QA) procedures in radiotherapy. The system implements a scintillation-based phantom and associated signal acquisition and processing modules and aims to monitor two-dimensional (2D) dose distributions of small fields. Materials and methods For the proposed phantom, we have designed and realized a prototype implementing six high-resolution tissue-equivalent scintillating fiber ribbons stacked with in-plane 30 degrees rotated orientations from each other. Each ribbon output is coupled to a silicon photodiode linear array (with an element pitch of 400 mu m) to detect scintillating signal, which represents the projected irradiation profile perpendicular to the ribbon's orientation. For the system providing six acquired projected dose profiles at different orientations, we have developed a two-step signal processing method to perform 2D dose reconstruction. The first step is to determine irradiation field geometry parameters using a tomographic geometry approach, and the second one is to perform specific penumbra estimation. The QA system prototype has been tested on a Novalis TrueBeam STX with a 6-MV photon beam for small elliptic fields defined by 5- and 10-mm cone collimators and for 10 x 10- and 20 x 10-mm(2) rectangular fields defined by the micro-multileaf collimator. Gamma index analysis using EBT3 films as reference has been carried out with tight 2%-dose-difference (DD)/700-mu m-distance-to-agreement (DTA) as well as 1%-DD/1-mm-DTA criteria for evaluating the system performances. The testing also includes an evaluation of the proposed two-step field reconstruction method in comparison with two conventional methods: filtered back projection (FBP) and simultaneous iterative reconstruction technique (SIRT). Results The reconstructed 2D dose distributions have gamma index pass rates higher than 95% for all the tested configurations as compared with EBT3 film measurements with both 2%-DD/700-mu m-DTA and 1%-DD/1-mm criteria. 2D global gamma analysis shows that the two-step and FBP radiation field reconstruction methods systematically outperform the SIRT approach. Moreover, higher gamma index success rates are obtained with the two-step method than with FBP in the case of the fields defined with the stereotactic cones. Conclusions The proposed small-field QA system makes a use of six water-equivalent scintillating detectors (fiber ribbons) to acquire dose distribution. The developed two-step signal processing method performs tomographic 2D dose reconstruction. A system prototype has been built and tested using hospital facilities with small rectangular and elliptic fields. Testing results show 2D reconstructed dose distributions with high accuracy and resolution. Such a system could potentially be an alternative approach to film dosimetry for small-field QA, which is still widely used as reference in clinical practice.